PAN EVAPORATION: - Hawaii.gov

PAN EVAPORATION: STATE OF HAWAI'I,

1894-1983

Report R74

State of Hawaii DEPARTMENT OF LAND AND NATURAL RESOURCES

Division of Water and Land Development

PAN EVAPORATION: STATE OF HAWAI'I, 1894 -1983

Report R'74

Prepared by

PAUL C. EKERN and JEN-HU CHANG University of Hawaii at Manoa

WATER RESOURCES RESEARCH CENTER Honolulu, Hawaii 96822

In Cooperation with

HAWAIIAN SUGAR PLANTERS'ASSOCIATION Aiea, Hawaii 96701

State of Hawaii DEPARTMENT OF LAND AND NATURAL RESOURCES

Division of Water and Land Development

Honolulu, Hawaii August 1985

GEORGE R. ARIYOSHI Governor

BOARD OF LAND AND NATURAL RESOURCES

SUSUMU ONO, Cha i rpe r son , Member at L a r g e

MOSES W. KEALOHA, Member at Large

J. DOUGLAS ING, Oahu Member

ROLAND 14. IIIGASIII, Elawaii Member

JOHN Y. ARISUMI, Maui Member

LEONARD H. ZALOPANY , Kauai Member

DEPARTMENT OF LAND AND NATURAL RESOURCES

SUSUMU O N 0 , Chai rpe r son a n d Member Board of Land and Natura l Resources

EDGAR A. HAMASU, Deputy t o t h e Cha i rpe r son

MANABU TAGOMORI, Manager-Chief Eng ineer Division of Water and Land Development

ABSTRACT

Pan evaporation measurements i n Hawai' i began as early a s 1894 and

eventually included intermittent observations a t over 200 s i tes , the majority w i t h stainless s tee l C l a s s A pans s e t on 5 f t high platforms. Sites were concentrated i n the dry lawland irrigated areas but shielded evaporimeter transects extended measurements into high rainfall areas.

Evaporation a t s i t e s with 20-yr records had a nearly normal distribution for which the standard deviation decreased from nearly 30% of the mean for daily, t o 15% for monthly, and t o 7% of the mean of annual values.

Ehpirical relationships between evapration and temperature or rainfall had only limited applicability .

The pattern of annual evaporation for each island differed from the equilibrium value of 80 in. over the ocean as patterns of cloudiness, sunlight,

and rainfal l changed i n response t o wind flow over the island topography. Be-

neath the tradewind orographic clouds, evaporation was 30 t o 40% less than the

oceanic rate, while in the d q leeward areas evaporation w a s 30 t o 40% more than oceanic, with summer rates greater than 12 in./mo. In the dry, sunny,

and windy s i t e s above the 6000 f t tradewind inversion level, evaporation again increased t o equal surface rates.

0 pan maprat ion, evaporation pans, evaporation rate, evaporimeters, net radiation, temperature, wind; C l a s s A pans, sunlight, Hawaii, Maui, Molokai, Lanai, Oahu, Kauai

Recognition must be given for the gathering and initial screening of many

of the pan records by the Hawaiian Sugar Planters' Association and its member

companies, and, in prticular, for the coordination by and cooperation of

Karl T. S. Haw, HSPA Associate &teorologist and Ehvironmental Specialist . Additional data from the University of Hawaii, Institute of Tropical

Agriculture and Human Resources came from Dr. Richard E. Green and Dr. Gordon Y. Tsuji of the Benchmark soils project. Dr. James 0. Jwik, Professor of

Geography, University of Hawaii at Hilo, and his helpers conducted the evap rimeter transect studies and furnished new data for Hawai'i Island.

Dennis Nullet, Shan-hsin Chiang, and Peter Matsunaga performed valiant service in the collection of the rccords, survey of field sites, and trans-

mutation of the data into computer format.

Mr. Saul Price of the National Weather Service and Mr. Thomas S. Nakama

of the Division of Water and Land Developnent, Department of Land and Natural

Resources, State of Hawaii, were frequently consulted in the establishment of

state index site particulars. Faith N. E'ujimura contributed far beyond the

routine duties of WRfZC Editor and is specially commended for her efforts that

brought this manuscript to completion, with the assistance af the WRRC Publi-

cations Office staff: particularly, April W.L. Kam, graphics illustrator, and

Patricia Y. Hirakawa for their meticulous checking and corrections of pan site

locations; and Jean M. Nakahodo for the preparation of the manuscript.

Dim- . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

. . . . . . . . . . . . . . . . . . . . . . . . . . . Pan Evaporation 4

Other J3vaporheters . . . . . . . . . . . . . . . . . . . . . . . . . 12

EM?IRIC9Z; AND PSEUDO-PHYSIC?& WE;LS FORPAN-RATION . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

PAN EVAPORATION RWOm I N HAWAItI . . . . . . . . . . . . . . . . . . . . 20

. . . . . . . . . . . . . . . . . . . . . PAN EVAPORATION MAPS FOR W A I t I 26

Wti . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

M1okati . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Ot&u . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Kaua'i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Maui . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

H L I W i l . j t i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 . . . . . . . . . . . . . . . . . . . . . . USE OF PAN EVAPORATION REXDRIxs 48

Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Crop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

REF-CITED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Figures

1 . Evaporation Along IGnoa and Kipapa Transects a s Function of Sunlight. Otahu. 1981 . . . . . . . . . . . . . . . . . 9

2 . Fraction of Sunlight Used i n Monthly Pan Evaporation as Function of Wind. Eaauka Campus (Sta . 7U.501, . . . . . . . . . . . . . . . . . . . . MZnoa Vdlltry. Otahuf 1980-1984 10

3 . EVaporimeter vs . Pan Evaporation Measurements. Average Monthly Values. Mauka Cam- (Sta . 713.50) . Einoa Valley. O'ahu. 1980-1984 . . . . . . . . . . . . . . . . . . . . 14

4 . Evaporation (logarithmic) vs . Median Rainfall (Maui. Kaua'i. Hawai'i. and O'ahu) . . . . . . . . . . . . . . . . . . 17

5 . Pan and Evaporimeter basurements and Calculations vs . Median Rainfall for IGnoa Valley and =papa Ridge Transects. O1ahu . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6 . Pan and Evaporimeter Measurements and Calculations vs . Reciprocal of Median Rainfall . . . . . . . . . . . . . . . . . . 19

. . . . . . . 7 . Evaptimeter Measurements vs . Elevation. Hawai'i Island 20

8 . Evaporation Trends as Influenced by Pan Canpsition and Color . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

9 . Probability of Annual Pan Evaporation for O'ahu . . . . . . . . . . . . . . . . . Stations 740 30. 737 .OO. and 826 -00 23

10 . Probability of Annual Sunlight. Makiki-Holmes Hdll. Honolulu. Hawai'i. 1932-1984 . . . . . . . . . . . . . . . . . . . . . 24

11 . Probability of Annual Hours of Bright Sunlight. Honolulu. 01ahu.1904-1983 . . . . . . . . . . . . . . . . . . . . . . 25

12 . Pattern of Monthly Pan Evaporation for Selected Station. LZim'i . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

13 . Pattern of Monthly Pan Evaporation for Selected Stations. Moloka'i . . . . . . . . . . . . . . . . . . . . . . . . . . 27

14 . Adjusted Annual Pan Evaporation for O1ahu . . . . . . . . . . . . . . 31 15 . Pattern of Monthly Pan Evaporation for Selected

Stations. O'ahu . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 . . . . . . . . . . . . . . 16 . Adjusted Annual Pan Evaporation for Kaua'i 36

17 . Pattern of Monthly Pan Evaporation for Selected Stations. Kaua'i . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

18 . Adjusted Annual Pan Evaporation for Plaui . . . . . . . . . . . . . . . 41 19 . Pattern of Monthly Pan Evaporation for Selected

Stations. Maui . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 20 . Adjusted Annual Pan Evaporation for Hawai'i Island . . . . . . . . . . 46

21 . Pattern of Wnthly Pan maporation for Selected . . . . . . . . . . . . . . . . . . . . . . . Stations. Hawai'iIsland 47

Tables

1. Sunlight Normalization Factors Based on Measured Sunlight and Hours of Bright Sunlight, Honolulu. . . . . . . . . . . . . . . . 11

2. Station Number, Period of Record, Measured Evaporation, Pan Type, and Adjusted Evaporation for L-a' i . . . . . . . . . . . . 26

3. Station N-r, Period of Record, Measured Evaporation Pan T y p , and Adjusted Evaporation for Wloka'i . . . . . . . . . . . 28

4. Station Number, Period of Record, Measured Evaporation Pan Type, and Adjusted Evaporation for Ogahu. . . . . . . . . . . . . 29

5. Station Number, Period of Record, Measured rnaporation . . . . . . . . . . . . Pan Type, and Adjusted maporation for Kauali 33

6. Station Number, Period of Record, Measured Gvapration . . . . . . . . . . . . . Pan Type, and Adjusted Evaporation for hui 38

7. Station Number, Period of Wcmrd, Measured Evapration . . . . . . . . Pan Type, and Adjusted Evaporation for Hawaigi Island 44

Although pan evaporation was first measured in Hawai'i as early as 1894 (Hawaii Weather Bureau 1897) and the USGS had several pan evaporation sites

in 1910 to 1911, the first significant pan observations were just after World War I when Class A pan evaporation sites were established at Maunawili Ranch

(Sta. No. 787.00) and Upper Hoaeae (Sta. No. 813.00) , with the data reported in the U. S. Weather Bureau Climatological Data. Several additional stations

were set up during the 1920 to 1930 period, but the majority of the pzn evapo-

ration measurements were begun in the mid- to later 1950s after World War I1

to aid in crop irrigation. These sites were concentrated in the dry leeward coastal areas where sugarcane was grawn.

Pan evaporation has been the principal measurement used in Hawai'i to

assess the amount of water use by crop. Assessment of the hydrologic balance requires measurement andlor calculation of evaporation from water and soil

surfaces, as well as evapotranspiration from plants. Agronomic crop production often can be directly related to the amount of transpiration, although

the water use efficiency of individual crops may be unique and can be changed

by agricultural practices (Winter 1981). Reservoir and lake evaporation

(Roberts and Stall 1966; Winter 1981) and potential evapotranspiration f rom

crops can be estimated with reasonable accuracy £ram evaporation pans with the use of appropriate predetermined constants (Doorenbos and Pruitt 1975; Stewart

and Hagan 1969) . Many agroclimatic procedures for water-budget effects on crop yields require open-water evaporation as an index (Stanhill l%2; Linacre

and Till 1969).

The pattern of evaporation over the Hawaiian Islands differs from that

over the open ocean, just as the pattern of rainfall and cloudiness is changed by the island topography. Computed evaporation from the ocean near Hawai'i

peaked in April near 0 -22 in./day with an extended period near 0.16 in./day

£ram July to January, which gave an annual rate of about 0.18 in./day or

65 in./yr (Seekel 1962, 1970) . Evaporation over the open ocean must approach the equilibrium postulated by the Priestly-Taylor approximation of the radiant

energy portion of the combination form of the Penman equation (Priestly and Taylor 1972) ,

where a is an empirical constant about 1.26, s the change of the saturation

vapor pressure with temperature, Y the psychrometric constant, so tha t

[s/(s + Y)I = sea level and 75OF = 0.61, R the net radiation, and G the sur-

face storage of heat. For Hawai' i, with an average sunlight of 500 cal/cm2/

day) (Ekern 1965a; Ekern and Yoshihara 19771, an ocean albedo of 0.05, a net

long-wave radiation balance of 100 cal/cm2/day) , and no net storage, equilib-

rium evaporation would be 0.19 in./- or 71.0 in./yr, i n close agreement with

the previous calculations based on vapor def ici t and transfer coefficients. W i t h an ocean/pan coefficient of 0.9, and evaporation from sea water 0.98 tha t

of fresh water (Turk 1970) , the anticipated Class A pan evaporation w e r the

open ocean adjacent t o Hawait i would be 79 in./yr. This evapration corres-

ponds t o an estimated 18 in. of annual rainfall wer the ocean (Reed 1980) . Most watersheds in H a w a i ' i are characterized by the relatively small

fraction of the annual rainfall which leaves the basin a s stream flow and,

consequently, the large fraction of evaporation. On central O1ahu, runoff is about 25% and evapotranspiration 30% (45 in. 1 of the 150 in. of annual rain-

f a l l for the upper KXpapa Stream basin (Mink 1962; Ekern 1983). For the Hono-

lulu area, runoff w a s estimated i n an early study as about 20% and evaptrans-

piration 50% (52 in. of the 104 in. of annual rainfall (Wentworth 1951) ; and recalculated for Honolulu, runoff w a s 20% and evaporation 40% (24 in.) of

65 in. of annual rainfall (Giambelluca 1983). Detailed evaluation of the

Pearl Harbor basin indicates 10% runolf and 39% (33 in.) evaporation of the

combined 60 in. of rainfall and 25 in. of irrigation (Gimnbelluca 1983).

Clearly, evapotranspiration is a major component of the hydrologic balance of

the island, and the value differs from that wer the open ocean.

Crop dry matter production i n Hawai'i depends on the amount of water

available from rainfall and irrigation. Sugarcane tonnage is a linear func-

t ion of effective water application (irrigation + rainfal l ) , while relative

cane yield (actual/maximum experimental yield) is also a linear function of

the relative water application (effective application/pan evaporation) for a ser ies of irrigation studies (Jones 1980). Californiagrass dry matter produc-

t ion under heavy irrigation with secondary treated domestic sewage is also

highly correlated with water use a s w e l l as linearly related t o the amount of

nitrogen supplied by tha t effluent (Handley and Ekern 1981, 1984).

Pineapple cultivated with both plast ic and trash mulch uses one-tenth the

water required for conventional grass vegetation (Ekern 1%5c, 1967). Direct

evaporation £run so i l drops t o as l i t t l e a s one-fourth the potential rate as

capillary conduction of water to the soil surface fails t o keep pace with

demand and the plane of vaporization retreats within the soil (Ekern 1%6a). Grass sod evapotranspiration cannot maintain the initial high rates (115%

Class A pan evaporation), but decreases progressively as the soil water stress

increases (Ekern 1966b, 1983). Evapotranspiration under sprinkler irrigation

can exceed by 15% that when only partial surface wetting occurs as with drip irrigation of sugarcane (Ekern 1977).

Thus, many basic difficulties face the prediction of evapotranspiration.

Direct measurement of all components of the water budget for entire watersheds

is almost impossible, but measurements of the components of the water budget

for artificial watersheds, lysimeters, or other evaporimeters can in turn be calibrated against water use of an actual watershed, Such waporimeters range

from large lysimeters (Ekern 1977) through pans (Phene and Campbell 1975;

Nordenson and Baker 1962; Davis 1963; Sims and Jackson 1971; Ekern 1%5b; Van

Eaveren and Farmer 1971) to atmaneters (Stanhill 1x2; Carder 1960, 1968;

Dilley and Helmnd 1973; Ekern 1983) . Many of these devices require an independent measure of rainfall. Errors

which result f ram rain gage size, exposure, and elevation can often be about 5 to 10% of the rainfall and obscure the evaporation measurement (Kalm et al. 1969; Larson and Peck 1974; Helvey and Patrick 1983). A10% error in evapora-

tion measuren~ents is usual when various methods of calculation and lysimetric

measurements are cornpared (Grant 1975; Cmnillo and Gurney 1984) . The accuracy rquired in the evapotranspiration value has been debated

when groundwater recharge is estimated as the difference among rainfall,

runoff, irrigation, and evapotranspiration (Wntworth 1951) , For the Honolulu

basin, a 10% error in evapotranspiration would be about 5 in. of the 50 in.

of evapotranspiration, or 17% of the 30 in. of recharge (Wentworth 1951) , or again 10% or 2.6 in. of the 26 in. of evapotranspiration and recharge

(Giambelluca 1983). For the Pearl Harbor basin, 3.4 in. would be 11% of the 30 in. of recharge from the 60 in. of rainfall (Giambelluca 1983). But for

the high rainfall area of Kipapa where evaporation is less and recharge greater, the 4.5-in. error in evaporation would be but 7% of the 67.5 in. of

recharge (Ekern 1983) ,

lPle tolerable error in the evaporation measurement and calculation depends on whether the intent is to describe the rannant recharge frgn the high

rainfall watersheds or the irrigation needs for the high evaporation crop

s i t e s i n the low rainfall areas.

This report w i l l review the pan evaporation measurements available for

Hawai i. ; translate auxil. iary evaporimeter measurements in to equivalent pan

values; extend the measured pan evaporation data by empirical relationships

with sunlight, rainfall, and elevation; and map the tabulated data for the

major islands.

Pan Evaporation

Many different types of evaporation pans have been used and although the

absolute values are not identical, the high correlatioii among different dim-

eter pan waporimeters fostered the use of a wide variety of pan sizes and

depths i n maporation studies (Davis 1963; Van Haveren and Farmer 1971;

Davenport 1967a, b; Iruthayaraj and Morachan 1978; Sims and Jackson 1971;

Hounam 1961; Kanehiro and Peterson 1977; Yu and Brutsaert 1967). The standard

C l a s s A pan has been used most frequently in Hawai' i (Division of Water and

Land Developent [DOWALDI 1961; Robinson, Car?pbell, and Chang 1963).

The standard Class A evaporation pan has been described in handbooks by

Doorenbos and Prui t t (1975, p. 51) a s follows.

The [Cllass A evaporation pan is circular, 121 cm (47.5 in.) i n diameter and 25.5 an (10 in.) deep. It is made of galvanized iron (22 gage) or mnel metal (0.8 mm) , The pan is mounted on a wooden open frame platform with its bot tm 15 cm above groundlevel. The so i l is bui l t up t o within 5 cml of the b t t m of the pan. The B n nlust be level. It is f i l l ed with water 5 cm below the rim, and [the] water level should not drop t o more than 7.5 cm below the rim. Water is regularly renewed t o eliminate extreme turbidity. The pan i f galvanized is painted annually with aluminum p i n t .

Brakensiek, rn, and Rawls (1979, pp. 230, 231) describe the measurement of

water i n the pan and discuss s i t e conditions as follows.

A micrometer hook gage is used with a s t i l l i ng well t o measure the level of water in the p. The brass s t i l l i ng w e l l provides an un- d i s t u r w water surface around the hook gage and a support for the gage. A small hole in the base allows water t o seep into or out of the brass cylinder. Leveling screws and lock nuts are prwided on the triangular base. e s t i l l i ng w e l l is located i n the pan about 1 foot (30.5 an) from the north edge.

lThe National Weather Service N ok (NQAA 1972) prescribes 1.27 crn (0.5 in,) rather than 5 an,

The hook gage consists of a movable graduated s tem w i t h a vernier. The graduated stem is f i t t ed on one end with a hook, the point of which touches the water surface when [the] water level is measured. When i n operation, the water level in Class A evaporation pans should be maintained a t 2 inches (5.08 cm) k l a w the rim, plus or minus 1 inch (2.54 cm). Water should be added or removed from the pan t o maintain th i s l w e l . This should be done a t the time of observation. The water lwel may be lowered below the usual limit when heavy rain- f a l l is forecast, thus avoiding loss of record due t o pan overflow.

Hook-gage readings of the water level in the s t i l l i ng well should be made daily. The micrmeter hook-gage point is lawered into the well until it is klow the surface of the water. The adjusting nut on the hook gage is then turned sluwly, raising the point unt i l it just pierces the water surface. The gage is removed f r m the well and the scale is read and recorded. Differences i n readings for consecutive days give the daily waporation amounts. When water is added or removed from the pan, hook-gage readings must be made before and after the water level change. Amounts added or removed are thus con- sidered i n computing evaporation. Any rainfall between observations should be measured with a nearby standard gage and should be used i n computing pan evaporation.

The s i t e for a Class A evaporation pan should be f a i r ly level and sodded except in ar id regions where maintenance of an a r t i f i c i a l sod cover would induce unnatural mdification of climatic conditions. Obstructions should not be closer t o the pan than four times the height of the object. W e e d s and grass should be w e d t o keep gr belaw the level of the pan. Sites on the downwind side of large swamp or reservoirs should be avoided. Evaporation pans should not k located near large paved areas such as parking l o t s or airport runways. The site of the waporation pan should be fenced t o prwent anirnals from drinking f r m the pan, and the water surface should be kept f ree of shadows. When ~ n s are installed over water or sunk i n the ground, similar restrictions apply.

Autcxnation of pan evaporation recording has acquired renewed value where

dr ip irrigation requires frequent autmatic measurement t o replace evapotrans-

piration losses in high-frequency irrigation systems (Phene and 11

1975). A shallow constant level pan evaporimeter was designed for rainy areas

i n Hawai'i with continuous record from a f loa t recorder on the water s w l y

tank (vanlt Woudt 1960, 1963) with comparable waporation rate and greater

precision during rainy periods. The role of inaccurate rainfal l msuranents

and the change i n heat budget with rainfal l makes it essential that pan w a p ration be shielded f r m rain i f accurate evaporation values are t o be obtained

(Bloemen 1978) . Modification into a constant l w e l recording pan reduced waporation t o

0 -94 that of an adjacent standard Class A pan over a period of about a year

( C a m e l l , Chang, and Cox 1959; Ekern 1960) . Tbe ntenance of a constant

water level by continuous pumping from a reservoir whose stage is recorded,

allows continuous record of the evaporation rates and does not require

independent measure of rainfall, although loss by raindrop splash still

renains a source of error i n the measurments (Richards and Stumpf 1966).

The galvanized pan has often been painted or changed t o monel or stainless steel t o offset corrosion. Monel reduces evaporation 1% below that of a

shirly new galvanized pan while stainless s tee l or aluminum paint reduces

evaporation 8% below that for a darkened or black painted galvanized pan, and

white paint reduces evaporation a s much as 22% belaw that for a standard galvanized pan (Young 1947; Nordenson and Baker 1962). For shallow pans, white

paint causes an even greater reduction t o about 0.6 that of a black painted

pan only 2 in. deep (Yu and Brutsaert 1967) . The National Weather Service

mandated a change t o a monel pan i n 1962. Many of the galvanized pans used i n

the sugarcane studies were painted aluminum and stainless s tee l pans were used

i n most recent studies. Evaporation measured from aluminum-painted pans and from steel pans is increased by a factor of 1.08 for comparison with a stan-

dard galvanized or mnel pan for this study.

The C l a s s A pan gains much of its heat through the bottcan and side, and

an insulated pan has 30% less evaporation than a standard pan (Wartena and Borghorst 1960; Riley 1966) , The mpir ical psychrometric constant, Y, for a Class A pan is double, and for an insulated shallow pan, about 10% greater

than that for a wet bulb psychrometer (Yu and Brutsaert 1967). The theoreti-

cal constant frcan a w e t bulb t h e m e t e r is defined as

where Cp = specific heat of a i r a t constant pressure, P = atmospheric pres-

sure, e = rat io of density of water vapor t o that of dry a i r , L = latent heat of vaporization of water (Brunt 1941; Storr and den Hartog 1975; Stigter 1976;

Ripley 1976).

The Bawen rat io of an evaporating surface is convective exchange of heat

divided by vapor exchange of heat and equals t o Y(Ts - Ta)/(es - ea>, where Ts is the surf ace temperature and Ta the temperature of the a i r stream, and es

the saturation vapor pressure a t the surface temperature, and ea the vapor

pressure of the a i r stream. Since the relative wmective exchange decreases

w i t h a i r pressure, the relative vapor exchange must increase with elevation as the value of Y decreases. The value of y is principally determined try a i r

pressure and, t o a lesser degree, by temperature and t o a still lesser degree

by relative humidity (Storr and den Hartog 1975) . This difference in the em-

pirical value for Y derived from the Bowen ra t io makes problematic the rat ios between pans of different sizes and depths with different rate of heat

exchange through the pan side and bottom, although the evaporation rates

between pu?s may be highly correlated (Davis 1 x 3 ) . Ehpiricdl relationships between evaporation and area of the water surface

finds evaporation a function of (area%-o1a for large lakes, (arsa)i)-&13 for smaller pans, and (area%) t o -ax (Brutsaert and Yeh 1970) . Y e t the

uncertainties i n the corrections among pans with different diameters and different depths are such that no correction is reammended for nonstandard pans i n t h i s study.

Evaporation is reduced 9% when the water level is kept a t 4.5 in., rather

than the recommended 2 t o 3 in. below the pan rim (mrdenson and Baker 1962). Although it is recognized tha t pins read weekly often have reduced evaporation

when the water level is low, no attempt is made t o correct the value for the water level.

For protection against animals and t o help offset the effect of expo-

sure on a pan in a snall enclosure surrounded by crops, such as 15 f t high sugarcane, marry puzs are placed on platforms 5 f t above the so i l surface. A t the Hawaiian Sugar Planters1 Association (SPA) Kunia Substation, for the years 1964 through 1981, pan evaporation a t 5 f t was 74.22 in./yr, while

waporation from a pan a t 1 f t was 66.46 in./yr (Ekern 1977). A l l elevated Class A pan evaporation values are adjusted i n this study t o reduce the

measurement t o an equivalent surface pan for the map analyses. Wire screen aver the pan t o prevent animals from drinking shades the pan

and reduces w i n d flow so that a 2 in. mesh screen reduces evaporation an average of 12.8% i n the humid southeast United States ( ~ 1 1 and Phene 1976) . In H a w a i t i , such a screen reduces evaporation from a shallow (1 in. deep) pan

about 5% (van' t Woudt 1963) . Pans used by Oahu Sugar Cmpany on their cane f ie lds on O1ahu have a protective screen around the pan rim but no measurement w a s made on the effect on evaporation. The screened pan evaporation is increased by a factor of 1.05 for comparison with a standard unscreened pan i n t h i s evaluation for the map analyses.

When the recomn\ended well-watered grass sod does not surround the pan

s i t e , advection of heat from the dry surroundings can increase evaporation rates as much as 50% and magnify the differences among pans of different sizes

(Dale and Scheeringa 1977). Pan evaporation rates within sugarcane fetch must

fluctuate with the moisture status of the upwind cane, particularly during the rimning period when irrigation is stopped and during the replanting period

when evapotranspiration is reduced and the shelter effect of the pan greatly changed (Ekern 1977). No systematic correction is made for th i s effect on pan evaporation records.

Pan evaporation a t the Pineapple Research Insti tute (PRI) Waipio site had a linear response t o wind (Ekern 1960, 1%5b) . Although a p e r relationship could also be made, many enpirical evaporation fonnulas for ponds and lakes use a linear wind function (Brutsaert and Yeh 1970) . The original Penman ccinbination of the radiation and aerodynamic formulas also uses a linear wind function (Skidmore, Jacobs, and Powers 1969) .

The shelterbelt action of buildings or t rees can reduce pan evaporation by as much as 35% (Carckr 19681, but this effect can be reduced to l ess than 10% i f l i t t l e or no positive advection occurs and the radiant budget dominates the energy supply for evaporation (Lanas and Schlesinger 1971; Blundell 1974; Hanson and Rauzi 1977) . The wind reduction i n the shelter l e e has a

much greater effect on atmumeters, such as the Piche, where the aerodynamic term dominates the evaporation, and w a s so reported (Lomas and Schlesinger

1971) , but the other atmmeters used i n the l ee of porous windbreaks indicate a 40% reduction i n evaporation by these barriers, greater and more extensive

than that for a solid barrier (Skidmore and Hagen 1970) under positive advection.

Sane index of wind velocity might be used t o normalize the pan evapora- t ion measurements f r m different years. Possible indexes are anomalies i n the

northeast tradewind area and wind s t ress (a function of v2) reported for the

northeast trades since 1949 by Wyrtki and Myers (19761, and since 1976 by Sadler, Ramage and Hori (1982) and Sadler and Kilonsky (1981) . In general the wind stress w a s below normal fxan 1948 to 1955 and above normal after 1955

except for the E l Nifio incursion. Hawever the Hawaiian Islands mechanically dis tor t the trade winds and

create many local departures £ram the average tradewind stream (-age 1978, 1979) . The suggested streamlines of wind flow for O'ahu (Noguchi 19791, Maui (Daniels and Schroeder 197 8) , and Hawai i (Mendonca 1% 9; Mendonca and Iwaoka

1969; Ekern and Garrett 1979; Schroeder 1981; Ekern and Becker 1982) a re so complex that no adequate index is available t o use for the different leeward

and windward pan sites; thus, no correction is made for wind i n normalizing

the p n evaporation records.

Island topography controls t o a large extent the sunlight patterns be-

cause orographically induced clouds and rainfal l are dominant features of the climate (Blumenstock and Price 1961; Ekern 1978) . Sunlight and consequent net radiation so govern evapration, particularly in the high rainfall areas, tha t

an index of sunlight must be developed t o normalize the miscellaneous years of

pan evaporation record (Fig. 1). The sensitivity to wind velocity was such

that once wind exceeded 40 miles/day, further doubling of the wind increases

by only 10% of the fraction of sunlight used i n evaporation for Wahiawa and

a four-fold increase from a 55 t o 200 miles/day wind run only 30% for the

lvIi1ilan.i site (Ekern 1960) (Fig. 2) . Measured sunlight values for Honolulu since 1921 are about 3% belaw

normal during the 1930s, ranain about 5% above normal from the mid-1950s t o

Pan

0.3

- r r[l u \

.f 0.2 V

0 0 0.4 0 0.3 0.2 0.1

SUNL l GHT [ ( c a l /cm2/day) /I5001

I I

Q Monoa \ Trnnsect \ \ \,A Pan (713.50)

- 9 - \ \

NOTE: Latent heat for 1 in. evaporation = approx. 1500 cal/in.

Figure 1. Evaporation along MZma and Kipapa transects a s function of sunlight, Ot ahu, 1981

5 T t WIND ( m i l e s / d a y )

NOTE: Latent heat for 1 in. evaporation-approx. 1500 cal/in.

Figure 2. Fraction of sunlight used i n monthly pan waporation a s function of wind, Mauka Campus (Sta. 713.50) , Einoa Valley, O'ahu, 1980-1984

mid-1%0s, then decrease progressively t o about 5% below normal during the

1 9 7 0 ~ ~ and have the lowest value of record, 13% below normal in 1982. Prior

t o 1932, only hours of bright sunlight were recorded. Hours of bright sun-

l ight for the PRI Waipio site were used t o evaluate the relationship t o the

Angot value and gave the equation (Ekern 1%0),

This relationship is used t o normalize pan evaporation measurements prior to 1932 and the measured energy values used af ter 1932 (Table 1) .

Because the vapor deficit , which governs evaporation rate, depends ex-

ponentially on surface temperature, and the temperature deficit , which governs

sensible heat loss, depends l inearly on surface temperature, small changes i n

the surface temperature can balance large changes i n net radiation and heat-

ing. Tropical water surface temperatures are buffered against large variation

by evaporation (Priestley 1966; N w e l l 1979; Hoffert et al. 1983). Tropical

TABLE 1. SUNL1.m N O ~ I Z A T I O N FACTORS BASED ON MEWURED SUNLIGHT AM) HCeTRS OF BRIGEPT SUNLIGHI', HONaJLULU, WAWAI ' I

Year Sunlight Epplg~ Hour Year Sunlight

Hour Q?PlqY

sea surface and freely evaporating leaf temperatures cannot go above about 86OF because a t higher temperature loss of energy by evaporation exceeds the energy input. Ocean temperatures near Hawai' i of about 77OF are just below

this cr i t ica l maximum value. Pan water temperatures for Hawai'i average about

75OF near sea level, w i t h maximum values of about the c r i t i ca l 86OF. Pan water temperatures have not been measured for most p n s i n Hirwai' i, but a re r ep r t ed for the Nationdl Weather Service stations.

Other Evaporimeters

The Piche evaporimeter, which measures water loss from a 1.25 in. diameter white f i l t e r paper, has been used t o a very limited extent i n Hawai'i. This instrument measures the wind term of the Penman combination evaporation

equation since it responds primarily t o the vapor def ic i t and wind velocity (Stanhill 1962) , and, is not a satisfactory instrument for measuring the

evaporation potential of the air . The Livingston atmameter measures water loss from a hollow porous

ceramic sphere about 2 in. in diameter w i t h one-eighth inch t h i c k w a l l s . Both

black and white Livingston atmometers have been used i n Hawai'i (Ekern 1965b; Noffsinger 1961). Sunlight and pan evaporation are poorly correlated wen w i t h the difference between the black and white instruments, in contrast t o reported correlation r 2 values of nearly 0.8 from other areas (Halkias, Veihmeyer, and Hendrickson 1955; Ekern 1965a; and Jones 1980). No extensive data are available for Livingston atmameter studies i n Hawai'i.

The Bellani plate atmmeter measures water loss from a f l a t porous ceramic surface 3 in. i n diameter. From black plates, correlation with Class

A pan evaporation i n H a w a i ' i have an r 2 value of 0.735 (Ekern 1%5b). The Bellani black plate correlates with the meteorological elements of sunlight,

temperature, wind, and vapor def ic i t much l ike a Class A pan (Pelton 1963) , although the relative irnprtance of wind is slightly greater for the pan than

for the atmaneter, and the simple correlation between the plate and the pzn has an r value of 0.84. The Bellani plate has also been highly correlated w i t h measured evapotranspiration of wheat and grass, with absolute values of

water use 0.88 that of the plate when the crop surface is frequently wetted

and water is not limiting (Carder 1968). Flat, porous sponse ataxmeters w i t h

the surface shaded and unshaded are also shown t o have an r 2 correlation of 0.9 with net radiation and give accurate estimates of potential evapotrans-

piration i n an Australian study (Dillqr and Helmnd 1973). No extensive data with Bellani plates exist for Hawai i.

Rain-shielded, dark, f l a t , porous corundum evaporimeters have s h m high correlation with sunlight and pan evaporation for transect studies on OBahu (Wilcox 1962; Ekern 1983) with a composite daily summer r 2 value of 0.716 for

1981 and weekly values of 0.827 for June 1980 through May 1981. Pan evapora- t ion adjusted t o an equivalent galvanized surface pan for the University of Hawaii Mauka Campus (Sta. No. 713 .50) is 0.53 the evaporimeter rate and about

0.66 of sunlight during the summer months when rainfal l was leas t disruptive (Fig. 3 ) . Extensive data on O'ahu and Hawaili are used to extend the measured

evaporation by a galvanized iron surface pan value equivalent t o 0.53 the evaporimeter measure.

Several styles of s m a l l open water evaporimeters have been reported

(Davis 1963; Davenport 1%7a, b; Davenport and Hudson 1967; Sims and Jackson 1971; Van Haveren and Farmer 1971) . Although many of these evaporimeters a re

highly correlated with Class A pan evaporation, the absolute values could not be predicted. A modification of an insulated pan evaporimeter was used a t

several s i t e s on Haw& ' i (Jwik, Singleton, and Clarke 1978) . maporation f ram the snall screened insulated pan on Hawai' i has a linear decrease with elevation from sea level t o 6500 f t , and corresponds roughly t o an adjusted fraction of a Thornthwaite calculation 01 expected evaporation.

World-wide lysimetric measurements of water use i n evapotranspiration by

many c r o p have been reviewed and appropriate factors for translation of Class A pan evaporation into water use of crops presented (Doorenbos and Prui t t 1975) . Pan factors for crop water requirements for Hawai' i have been establish& from lysimetric studies on O'ahu and Maui with sugarcane, pine-

apple, and grasses (Stearns and Vaksvik 1935; Stearns, Swartz, and Macdonald 1940 : Campbell, Chang and Cox 1959: Robinson, C a m p b l l , and Chang 1963; Ekern 1x5-1978; Jones 1980; Handley and Ekern 1984) .

With appropriate selection f ran these factors, pan evaporation measurements can be translated into actual evapotranspiration. The relationship of the consumptive use coefficient t o the description of vegetation has been the

focus of many modeling effor ts tha t continue t o refine the parameters neces-

STAl NLESS STEEL PAN (in./day)

WlX: Stainless steel C l a s s A pan a t 4-ft elevation.

0.5

-- 0.4 lz .- V

lx w

t; x - oC Q a 2 0.3 w

0.2

0.1

Figure 3. Evapor imeter vs. pan evaporation measurements, average monthly values, Mauka Campus (Sta. 713 -50) , MZnoa Valley, O'ahu, 1980-1984

I

/ / / /

l / /

Pan = 0.55 7' Evaporirneter /

- / czr -

/ A .

k /.a

./% ' 0;'.

- t l - 3 Z / a *

/ . /

; a/ l + / l

* I /

- a/. - . a I ma;'

0

l / /a / / / /

- / I

- I

I /

/ / / /

/ / / I I I

0 -

0.1 0.2 0.3

sary t o define these coefficients (Woo, Boersna, and Stone 1966; Ritchie 1972;

Culler, Hanson, and Jones 1976; Bur t e t al. 1981; Federer 1982) . Yet for

irrigated c r o p i n California with strong sensible-heat advection £ram dry

upwind areas, pan evaporation is the least reliable predictor of water use

compared t o four empirical or pseudo-physical models (Shouse, Jury, and Stolzy 1980) .

EHPIRICAC AND PSEUDO-PEIYSIQU; MODES JKlR PAN EXUORRl'ICN

Since hydrologic balance measurements for pans and other evaporimeters

have not been made for many parts of Hawai'i, empirical correlations and

pseudo-physical combination energy balance-mass transfer models have been

developed based on more commonly measured meteorological parameters.

In continental areas where air temperature more nearly correspnds t o the

amount of sunlight, empirical relationships between evaporation and a i r temperature have been used t o estimate evaporation (Criddle 1953; Baver 1954;

Holdridge 1959; Brutsaert and Stricker 1979; and, especially, Thornthwaite

1948) . The Thornthwaite relationship was found t o f i t reasonably well for temperature up t o 68OF i f adjusted and was used t o extrapolate evaporation

rates f r m the insulated pans on Hawai' i Island (Jwik, Singleton, and Clarke

197 8) . Because a i r temperature i n Hawai ' i is greatly modified by the marine

surroundings, temperature is not a reliable index of sunlight and generally is

a poor predictor of pan evaporation (Ekern 1960-1965) . In Hawail i there are

relatively few stations for which a i r temperature data are available, but gen-

eralized relations of temperature and elevation can be dram f r m the radio-

sonde measurements.

Rainfall observations i n Hmai'i have been made a t same 1500 sites, and

form the most nearly complete set of observation points over the islands.

Pan evaporation observations, separated into those w i t h lcw w i n d (less than

20,000 rniles/yr) were presented for O1ahu by Takasaki, Hirashima, and Luke

(1969) a s

log E = 1.9387 - 0.0035R (in./yr)

where log E = logarithm of evaporation (in./yr) and R = median annual rain-

fa l l . The revised relationships are log E = A + B x median rain£all for the

four major islands :

No. Avg; Island Cases GvaP. - A B r 2 - H a w a i ' i 23 69.07 1.99 -0.001 0.21

Maui 23 24.23 2.00 -0 .001 0 -39

0' ahu 3 5 42.14 1.99 -0 -003 0 -63

Kaua i 45 45 -00 1.97 -0.002 0.23

* In inches p r year.

A l l A values are slightly greater than the 1.9387 reported by Takasaki,

Hirashima, and Lubke (1969) , and the slopes of the Maui and Hawai1 i equations

markedly less than the 0.0035 of Takasaki. Consequently, evaporation predict-

ed for a 20-in. rainfall is 10 t o 20 in. greater and for a 150 in. rainfall ,

10 in. greater for the O'ahu or Kaua'i equations, and 35 in. greater than the

Takasaki prediction when the Maui or Hwai l i equation is used.

An wen simpler anpiricism held annual evaporation = 3600 in./yr annual rainfal l (Mink 1 x 2 ) which resembles tha t plotted from pan evaporation data

for O'ahu and Maui (Caskey 1968) . Recent extension of evaporation measure-

ments into the high rainfall areas on O'ahu suggest tha t neither of these

relationships are general enough for unrestrained a ~ l i c a t i o n t o Hawaili

(Figs. 4, 5, 6) . These relationships between annual rainfal l and annual

evaporation might be extended t o monthly relationships based on the inter-

relationship of annual and monthly rainfalls (Stidd and Leopold 1951).

A t elevations above the 6000 f t temperature inversion which characterizes

the structure of trade winds, sunlight is more intense, the relative humidity

drops belaw 30%, and the l aw level ra infal l and evaporation relationships are

not valid (Wndonca and Iwaoka 1969) . Measured evaporation beneath the cloud deck on O1ahu and Hawaili de-

creases with elevation in accord with the decrease i n temperature, increase i n

humidity, and general increase i n cloudiness as on H a w a i ' i Island (Fig. 7).

The average temperature and humidity profiles derived Frcan radiosonde

measurements i n the f ree air are distorted by a i r flaw along the mountain

slopes so that the summit of HaleakalB at 10,000 f t and the Mauna Loa Observa-

tory a t 11,500 f t have frequent daytime incursions of mist a i r from beneath

the tradewind inversion.

20 30 40 50 60 70 80 90 100 110 120 130 l40 I I I I I I I I I I I I -

MAUl - log E = 2 . 0 0 - 0.001 ra in

80 - a - -----_ 0 ----_

70 - 0

- 0

0

60

50

40

30

I >- 1.

K

Figure 4. Evaptxation (logarithm) vs. mdian rainfall (Plaui, Kawfi, Hawaifit and Otahu)

- 0 O ---. 0 O - - -0 - -- --

0 0 -- -* - o -.. -* -

KAUA'I -- --_

0 l og E = 1.97 - 0 . 0 0 2 rain -

- - Maui

0 ~ o u o ' i

I I I I I

-

H AWA 1'1 - log E = 1.99 - 0 .001 ra in - _ _ _ _ _ _ _ _ _

a --- 3 70 - ---- W

60 - A A -

50 - -

20- I I 1 I I 1 I I I I I I I I *

40

30

2 0

--. A O'A H u --. - -.

log E = 1.99 - 0 . 0 0 3 ra in -"- - - 2 % -

- A -

A Hawoi'i 0 'ahu

I I I I I I I I I I I I I I

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

RAINFALL ( i n . / y r )

IWE: Takasaki et al. (1969) and Mink (1x2) calculated values.

Figure 5. Pan and evaporimeter measurements and calculations vs. median rainfall for MZma Valley and Kipapa Ridge transects, 0' ahu

ANNUAL R A I N F A L L ( i n . )

120 100 5 0 2 5 2 0

I I I I I

110 - i +

Mink"! -

i +

loo - i v o -

v " i o

90 - -

h

r 80- -

-

W

-

-

Selected Pan Evaporation Stot ions

A ~ ' a h u (Woialuo) 0'ohu (Windward) 0'ahu ( '~wa-waipahu)

R A I N F A L L - I ( i n . )

Figure 6. Pan and evaporimeter measurements and calculations vs. reciprocal of median rainfall

0.55 E V A P O R I M E T E R ( i n . / y r )

SOtJFCE: J.O. Juvik (1985): personal communication.

Figure 7. Evaporimeter measurements vs. elevation for H a w a i ' i Island

But a t 5500- t o 6000-ft elevations near the top of the tradewind clouds, evaporation increases again and a t the summit

of Mama Kea evaporation i n the dry air is as great or greater than a t lea level. This is con- trary to the general decrease in

evaporation reported for Califor- nia and was used i n extrapolating

pan ev-ration measurements t o high elevations i n the WS stu* of the mainland U.S. (Farnsworth

and Tharnpson 1982) . The alpine and subalpine vegetation on slopes of Mhuna Loa bear out t h i s extreme change in the ecological

zones near the trade inversion (Mueller-Dombois 1967) .

Evidence of the evaporation rate in the dry clear a i r above

the normal tradewind inversion is

too limited t o set with any cer- tainty the pattern of evapration

above the 4000- t o 5000-ft elevation on Maui and H a w a i ' i.

PAN I Z V A F Q ~ ~ RMX)RDS IN HIWAI ' I

An i n i t i a l publication of "Pan Evaporation Data, State of Hawaii" (IXMAT.D

1961) , covered the 1894 t o 1960 period w i t h records from 61 pan evaporation stations that had been established, although only 32 stations were still in

operation a t that time. Details of the pan, such as size, composition, color, and height, were tabulated for many stations. A second publication, "Pan

Evaporation i n Hawaii: 1894-1970" (DU&%D 1973331, extended the data s e t and included additional stations, but gave l i t t le detail on the gens. NQAA pub-

l ishes monthly and annudl data i n "Local Climatological Data: Hawaii and

Pacificn for a series of s ix pan evaporation stations which began i n 1919

(MXA 1920-19833, although only three a re currently i n operation and data from

Sta. Nos. 702.00 and 702.20 are combined as a single record. These data were

summed and s t a t i s t i ca l parameters presented through 1980 in the NOAA Technical

Report NWS 34 (Farnsworth and Thmpson 1982) . Although changes i n pan c a m p sit ion, color, and s ize were acknowledged, no correction was made for these

facts.

Critical attention must be paid t o the history of changes in the pan

camposition, color, and elevation. Uncritical acceptance of NWS published

data for s ta t i s t ica l analysis of Sta. No. 702.20 (Farnsworth and Thmpon

1982; Farnsworth, Thompson, and Peck 1982) actually represented a tremendous

trend with time that probably was a progressive leak i n the pan drainage valve

(Fig. 8). In truth, evaporation remained relatively constant a t nearby Sta.

No. 740 -50. For Sta. No. 1020.10, the sh i f t from a painted galvanized pan t o

a mnel pan i n 1963 caused a marked increase in the measured pan evaporation,

while evaporation decreased a t Sta. No. 87.00 (Fig. 8) .

Naps of pan station locations a re presented i n Appendix Figures A.1 t o

A.6 and a brief s i t e description is given i n Appendix Table A.1. Alternate

station names which have been used over the years a re in Appendix Table A.2,

and an alphabetical list of current station names i n Appendix Table A.3.

Ebaporation records a s reported for Hawai'i stations are contained i n

Appendix Table B.l, their s t a t i s t i ca l parmeters i n Appendix Table B.2 , and

adjusted values i n text Tables 2 t o 7. Probability plots of the mean annual pan evaporation for selected stations with values based on daily observations

were slightly curvilinear, but where weekly data were the basis, reasonably

linear values were a criterion for normal distribution (Fig. 9) . Probability plots of sunlight (1932 through 1984 for Makiki-Holms H a l l )

had an apparent bimodal pattern with a cluster of values near the upper

quarti le during the mid-1950s t o mid-1960s and another frcm the cluster near

the luwest quarti le i n the 1930s and again i n the 1970s (Fig. 10) . Hours of

bright sunlight from the period 1904 through 1983 had a more nearly linear

probability plot and approach normal distribution (Fig. 11) . For a normal population, the standard deviation and the mean deviation

y have the relationship, 2a2/y2 = T. This ra t io for Station No, 740 -50, with

19 years of annual pan data, is 0.94 -rr, and suggests near normality (Conrad

Figure 8. Evaporation trends as influenced by pan ccmpsition and color

1955 1960 1965 1970 1975 1980 1985

+-.+ Sto. 1020.10 ( G r a y galv.)

1.1

1.0

0.9

l ~ ~ ~ ' ~ ~ ' ' ' l ' i ' ' ~ ' ' ' ' ~ ' ' ' ' ~ ' ' l r ~ ~ + - GoIv. -Monel := Stainless -

- -

- -

- -

l l ~ l t l l t l l l l ~ l I 1 l l ~ ~ l l ~ ~ ~ l ~ l l l l l

1955 1960 1965 1970 1975 1980 1985

YEAR

.01 05 1 2 5 1 2 5 10 20 3040506070 80 90 95 9899 998

% BELOW INDICATED VALUE

Figure 10. Probability of annual sunlight, Makiki-Holmes Hall, Honolulu, Hawai'i, 1932-1984

1944).

The coefficient of variation (standard deviation as a percent of mean) of annual pan evalpration values of the leeward station 740 -50 (HEPA Kunia Sub-

station) is 4.46/65.8 = 6.8% for the 19-yr period beginning in 153. The

monthly coefficients have a maximum value of 16.6% in March and a minimum

value of 6 -93% in October. A windward site, station 87 -06 (Hilo Airport) has

an annual value of 5% with a maximum of 22.07% in December and a minimum of

8.98% in August for the monthly values. Daily pan evaporation at the Univer- sity of Hawaii Nauka Gunpis (Sta. 713.50) for June 1983 has a coefficient of

variation 25.6% of the mean pan evapration of 0 -25 in./day and for January 1983 has a coefficient of variation 33.5% of the mean of 0,138 in./day. The

coefficient of variation approximately doubles from annual (7%) to monthly

C 15%) , and doubles again to daily periods (30%) .

Figure 11. Probability of annual hours of bright sunlight, Honolulu, O1ahu, 1904-1983

>- 2 '. & 36 c.3 - -1 5 3 4 - V)

I-

3 3 2 - - & m

& 30-

V) cz

2 8 - I

w C1

$ 2 6 - w z -J 24 a 3 Z 2 a 20

.01

Based on the premise of small sample number (less than 30) from a normal distribution, the standard error of the mean, 2&, = s/&), where s2 = N 02/

(N - 1) for N observations.

I l l I I I I I I I I I I I I I I I . - 1904 - 1983 • -

.* 0. -

i : - i

d' -

f / .

- - e m

e m 1 1 1 1 1 I I I I I I I I I I I I I .

.05 1 2 .5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99

For the 5% coefficient of variation, &would encompass 68% of the values

with errors of 1% in 25 years and 1.58% in 10 years. However, for individual

% BELOW INDICATED VALUE

months-especially in spring and fall-with the coefficient of variation near

20%, the S ~ Z of the mean would be 4% after 20 years and 6% after 10 years.

The W S study (Farnsworth and Thompson 1982) omits pan wapra t ion

records for periods less than 5 yr and uses only evaporation t o the nearest

1 in./m for those with 5 t o 10 yr of record, with the presumption that a

minimum record of 10 years is required t o establish evaporation t o the nearest

0.1 in./m. The standard deviations of the longer records for sunlight for the 1960

through 1984 period (when many of the pan records were taken) have an annual sunlight coefficient of variation 25.44/487 = 5.2%, with the July value 5.9%

and the January value 10.4%. For the entire period of record (1932 through 1984) , the annual coefficient of variation is 26.38/484 = 5.3% with 9.3% in

January and 6.4% in July. The seasonal patterns resemble those for the pan

evaporation and the magnitude of the annual coefficients of variation are

almost identical, again supportive of the major role of sunlight in the deter- mination of evaporation rates.

PAN EVAFORATION M?iT?S FOR HZWRI ' I

Maps of evaporation were plotted for O1ahu, Kaua'i, Maui, and H a w a i ' i f r m the adjusted annual pan evaporation measurements, but were not prepared

for L h ' i with its single station or for Fbloka' i, with only three stations.

The mnthly evaporation was graphed for selected stations on each major island

t o demonstrate the seasorldl pattern of evaporation. The annual and diurnal

patterns of rainfall which depend on cloudiness, that i n turn affect sunlight

and evaporation potential, helped suggest the delineation of the evaporation

contours (IX)WALD 1982).

The single s i t e (Table 2) with its short period of observation cannot be

used t o predict the amount or pattern of evaporation. Qlly rainfall isohyets

are available t o suggest the pattern of evaporation. A t t h i s site on the

crest of m ' i h a l e , the persistent tradewind-generated orographic clouds off-

set the summer increase in potential sunlight so that the annual evaporation

is only one-third tha t aver the ocean and nearly uniform throughout the year

(Fig. 12).

TABLE 2. STM'ION NUM3ER, PERIOD OF REXDlU), EVAPORATION, PAN TYPE, AND A R J u m EVAPORATION FOR LANA' I

PERIOD ANNUAL m I o N PAN WrnRATION FACIOR AIU. ELeva- Other wAP* ?F Paint tion Notes Sun- ANNUAL

mW RECORD (in.) s l t lon - -- Pan l ight (in./yr) 687.00 1957-58 26.85 galv. surf. 1.0 1.05 25.6 * Adjusted annual = measured annual x pan correction -? sunlight correction.

Despite their brevity the three pan evaporation records (Table 3) reveal

the very high evaporation rates on the dry, windy uplands of central Molokali.

&en a t the 500- t o 800-ft elevation, annual rates are 30 t o 40% greater than

27

N

I C I T Y

Sta 687.00

Jan June Dec

UHM-WRRC -- --

Figure 12. Pattern of mnthly pan waporation for selected selected station, Iana1i

Sto. 528.30

MOLOKA'I

K A U N A K A K A I

UHM-WRRC

Figure 13. Pattern of monthly pan waporation for selected stations, lYolokali

tha t for the open ocean, and the markcd increase t o summer values more than

12 in./mo is evidence of the extreme positive advection of heat from the dry

surroundings during t h e peak tradewind season (Fig, 13)

TABLE 3 EVATION NUMBER, PERIOD OF REKDRD, klE3SUm EVAPORATION, PAN TYPE, AND A W U S E D EVAPOF?A!I'ION FOR MDLC;KA1 I

PEXOD STATION AIWUAL PAN E V ~ ~ I O N FACIY>R Am. EVAp. Eleva- Other Sun- ANNUAL*

NuMsnc RMX)RD (in.) s i t ion Paint t ion Notes Pa" l igh t (in./vr)

511.50 1980-83 80.8 s. s tee l surf. 1.08 0.93 93.8

528.30 1962-65 106.46 galv. surf. 1.0 1.05 101.4

531.10 1970-84 118.1 s. steel 4-f t 0.97 0.95 120.6

'Adjusted annual = measured annual. x pan m r r t r t i o n i sunlight correction.

0' ahu

Pan evaporation measurements i n the leeward lawland areas allow reason-

able definition of amounts and patterns of evaporation, but the windward

slopes and central hiwands have few measurements of pan evapration

(Table 4t Figs. 14 , 15). m e mountain ranges do not reach the tradewind

inversion so that the plethora of data and simplicity of wind flaw make the

patterns for th is the most complete for any of the islands.

On-shore flow where the trade winds sweep the north and south ends of the

island has increased mixing from the overland roughness that offsets the

greater reflection of sunlight so tha t pan evaporation is nearly identical

with that expected over the ocean. The summer peak in sunlight and tradewind

flaw also cause a summer peak i n evaporation.

The orographic cloud which forms over the mountain ridges reduces evapo-

ration t o about one-fourth that over the ocean with l i t t le seasonal change i n

monthly rates. Innnediately t o the lee of the Ko'olau crest, evaporation is l a w because of decreased sunlight and lw wind velocity, but evaporation in-

creases dawnwind as cloudiness decreases and winds couple back t o the surface

so that the central Wahiawa plain evapration is only reduced about 10% belm

that of the ocean.

Further t o the lee on the dry lE)wa-Wahi~a plain, positive heat advection

increases evaporation t o nearly 100 in./yr, 20% above that for the open ocean.

TABLE 4. SCATION ISUMBER, PERIOD OF RMX)RD, MENU?ED ENAPORAITION, PAN W E , AM) AIXTUSTED EVAPO~ION FOR 0' AHU

PERIOD ANNUAL m I O N PAN DESCRIPTION FACrOR m. Eleva- Other EVM* paint tion Sun- Annual* RECORD (in.) s i t i o n Notes Pan l i g h t (in./yr)

702.00 1956-60 74.56 galv. white surf . 1.2 1.05 85.2

702.20 1963-74 84.3 m n e l surf . 1.0 0.99 85.2 197 5-81 leak? 1982-83 82.2 1.0 0.91 90.4

707 .OO 1958-60 73.62 galv. Al 5 f t 1971-75 74.88

713 -50 1980-84 75-02 s. steel 4 f t 0.97 0.93 78.3

727.00 1963-83 93.39 s. steel 5 f t screened 1.02 0.97 98.2

732.00 1962-83 90.77 s. steel 5 f t screened 1.02 0 -98 94 .5

737 .OO 1962-83 84.51 s. steel 5 f t screened 1.02 0.97 88.9


740.30 1959-64 80.10 galv. Al surf . 1.08 0.99 87.4

740.40 1962-83 74.03 s. steel 5 f t

740.50 1963-83 65.62 S. Steel 1 f t

741.00 1961-83 80.82 s. steel 5 f t screened 1.02 0 -94 87 .7

751.20 1962-83 86.09 s. steel 5 ft screened 1.02 0.98 89.6

752.00 1929-30; 57.67 galv. Al surf . 1960

752.50 1960-63 74.41 galv. Al surf .


761.10 1962-67 71.2 s. steel 5 ft screened 1.02 1.04 69.8

772.60 1970-81 35.2 s. steel 1 2 f t 3 ' d i m 0.85 0.96 31.1

782.00 1931-36 35.57 galv. surf in grass 1.3 0.95 48.7

787.00 1920-30 44.37 galv. surf . 1.0 0.9 49.3

795.10 1957-60 73.59 galv. 4 f t 0.9 1.04 63.7

798.00 1939-47 74.12 galv. surf . 1.0 1.0 74.1

813.00 1911-15 62.17 galv. surf . 18"diam 1.0 0.91 69.0

815.00 1964-78 73.6 s. steel 5 f t screened 1.02 0.98 76-6

816.20 1980-81 71.8 s. steel 4 f t -97 0.99 70.4

816.30 1980-83 75.13 s. steel surf . 1.08 0.93 87 .3

WJX: Std. Class A pan is galvanized, unpainted, 4-ft d i m , 10 in. deep, and

* at surface. Adjusted annual = rcleasulred annual x pan correct ion + sunlight correction.

TABLE 4--C0nt inued

PERIOD ANNUAL SPATION PAN DESCfUIPTION FACTOR Aa7. Eleva- Other Paint tion Sun- ANNUAL

mm RECORD (in.) s l t lon Notes Pan l ight (in./yr)

s. s tee l

gaiv.

s. steel

s. s tee l

galv.

s, steel

galv.

s. steel galv.

s. s tee l

galv.

galv.

galv.

s. steel

s. s tee l

galv.

galv.

galv.

galv.

galv.

5 f t

surf.

5 f t

5 f t

surf.

4 ft

5 f t

surf.

5 f t

surf.

surf.

surf.

5 f t

5 ft

surf.

surf.

surf.

surf.

screened 1.02

screened 1.0

screened 1.02

20' ridge; 0.8 screened

14" deep 1.0

0 -97

1.08

0 -97

1.08

0 -97

1.08

1.08

1 *o .... 0 -97

i n weeds 1.3

1.08

0 -97

1.08

1.08

S t a 908 00

O'AHU N

Jon June Dec

Jan June Dec

Jan .une Dec

Jon June Dec Jan June Dec Jav June Dec

UHM-WRRC

Figure 15. Pattern of monthly pan evaporation for selected stations, O'ahu

Kaua i

The amounts and patterns of evaporation for the lowland areas are w e l l -

defined by the measurements (Table 5; Figs. 16, 17). Very few msurements were made on the central highlands and although the elevation does not reach

the average 6000-ft elevation of the tradewind inversion, uncertainty about the w a r d mixing of dry a i r from above the inversion precludes establish-

ment of real is t ic evaporation values for the central uplands. Onshore flow along the windward coast is similar in pattern and amount t o

the open ocean with evaporation rates i n the summer months about 50% greater than those for the winter months.

W i g h t reduces rapidly as clouds increase inland, and evaporation is less than 75% tha t of the ocean and relative summer rates much reduced even a mile from the coast.

Persistent orographic clouds over the central highlands reduce annual

evaporation t o as l i t t l e as 25% that of the ocean, and eliminate any sumex increase in the monthly rates.

Evaporation increases perhaps 10% above that of the ocean on the dry lee

coasts and plains where heat advection markedly increases the evapration rates during the summer.

TABLE 5. EZXL'ION NUMBER, PERIOD OF -RD, lviEASURED EVAPORATION^ PAN TYPE? AM> m u m Evzm3RATION FOR KAUA' I

PERIOD ANNUAL SrATION PAN DESCRIPTION FACTOR IUXT. Eleva- Other

NPo Paint tion sun- ANNUAL* mER ~ R D (in.) s i t ion Notes Pan l igh t (in./yr)

galv. galv. s. s tee l galv. s. steel galv. s. s tee l

s. s t ee l

s. steel galv. galv.

A l surf. Al surf.

3 it

Al surf. 3 f t

Al surf. 3 f t

Al surf.

surf.

unknown .... 0.97

'~djusted annual = measured annual x pan correction i sunlight correction.

TABLE 5--€0nt inued ___. -

PERIOD ANNUAL ixuYL"ON OF PAN DESCRIFTION FAC'IOR AIX7.

Eleva- Other ENAPo C Paint tion Sun- ANNUAL

mER ~ R D (in.) g-ltlon Notes pan l i q h t (in./yr) 940 -00 ........... galv. A l surf .

1960-83 87.4 s. steel 3 f t

941.00 ............ galv. Al surf . 1960-83 86.62 s. steel 3 f t

943 .OO 1910-11 51.01 galv. surf . 18" d i m 0.82 0.83 51.0

943.20 1961-62 72.90 galv. Al surf . 1.08 1.05 75.0

944 .OO ............ galv. Al surf . 1960-83 73.82 s. steel 3 f t

945.00 1962-83 .... galv. Al surf . 1967-80 77.89 s. steel 3 f t

962.00 1963-75 90 -47 galv. Al surf . 1.08 1.0 97.7

965.00 1969-70 87.66 s. steel 3 f t 0.97 1.0 85.0

965.10 1971-75 84.67 s. steel 3 f t 0.97 0.94 87.4

966.00 1961-75 84.11 galv. Al surf . 1.08 0.99 91.8

981.00 1963-75 77.65 galv. A l surf. l a t e r 3 ' 1.03 0.99 80.8

982.00 1965-75 78.61 galv. Al surf . later 3 ' 1.03 0.99 81.8

986.10 1960-83 78.37 galv. Al surf . l a t e r 3 ' 1-03 0.99 81.5

993.00 1961-83 69.76 galv. Al surf. later 3 ' 1.03 0.98 73.3

994.00 1976-83 64.78 s, steel 3 ft 0.97 0.94 66.9


1005.00 ............ galv. A l surf . 1961-83 66.96 s. steel 3 f t

1006 .OO ............ galv. A l surf . 1961-83 57.18 s. steel 7 f t


1013.20 1968-75 72.65 s. steel 7 f t

1014.00 1971-83 78.37 s. steel 7 f t 0.97 0.96 79.2 ............ 1015.30 196566 ..... galv. Al surf .


1020.10 1955-62 84.02 galv. grey surf . 1.0 1.0 84.0 1962-84 94.14 monel surf. 1.0 1.0 94.1 1955-84 95.6 1.0 1.0 95.6

1020.40 1962-83 82.83 galv. Al surf . s. steel 7 f t

PERIOD ANNUAL STATION OF PAN DESCRIIrI'ION FACIYlR AAJ. Eleva- Other Sun- ANWUAL

--- -- m a Cow Paint tion RECORD (in.) s i t i o n Notes Pan light (in./yr)

1026.00 1962-83 75.53 galv. Al surf. s. steel 3 f t

..... 1027.00 1982-83 S. steel 3 f t

1033.00 1982-83 77.32 s. steel 3 f t

1035.00 1962-83 63.99 galv. Al surf. s. steel 3 f t

1040.00 ............ galv. Al surf. 1%2-83 60.19 S. steel 3 f t

1061.00 1959-60 45.69 galv. surf.

1061 -30 1962-83 57 -32 galv. Al surf. s. steel 7 f t

1062.10 1965-83 68.71 S. steel 7 f t 0.97 0.98 68.0

1062.20 1960-69 64.84 galv. Al surf . 1062.30 1960-69 64.98 galv. A l surf.

1064.30 159-83 78.37 s. steel 7 f t

1066.00 1965-66 ..... galv. Al surf. ............ 1072.10 1911 48.6* galv. surf. 18" d i m 0.82 0.83 48.6

1082.00 1910-11 22.2* galv. surf. 18" d i m 0.82 0.83 22.2

1092.00 1964-83 52.38 s. steel 7 ft 0.97 0.95 53.5

1101.10 1969-83 74.31 s. steel 7 f t 0.97 0.95 75.8

1102.00 1964-66 57.79 galv. Al s u r f -

1104.20 1969-82 78.13 s. steel 7 f t

1110.00 1964-66 62.95 galv. Al surf. 1.08 0.95 71.6

1112 -00 1910-11 79 -86 galv. surf . 18" d i m 0.82 0.83 79.9

1114.00 1964-83 77 -0 galv. Al surf . s. steel 7 f t

1134.00 1962-67 t galv. Al surf .

1135-00 1962-66 t galv. Al surf .

1136 -00 1962-67 t galv. Al surf .

1141.20 196267 t galv. Al surf .

1143.00 1962-67 72.58 galv. Al surf.

1145.00 196465 t galv. Al surf.

1146.00 1962-65 77.41 galv. Al surf .

.... 1147.00 1964-65 t galv. Al surf . 1.08 1.03

*mimated value. +No s ing le complete year of record.

Maui

Extensive pan and sunlight observations on the central isthmus and the

W e s t k u i coast allawed amounts and patterns t o be delineated (Table 6;

Figs. 18, 19) . No observations were available for the West Maui highlands which rise t o just belaw the tradewind inversion, nor for the HaleakalZ summit which frequently m e t r a t e s through the inversion. The effect on evaporation

of diurnal changes observed i n ugp and down-slope flaw on the Haleakal'i slopes

has not been measured (Lyons 1979) . A t the upwind coasts, onshore flaw had evaporation of about 80 in./yr,

similar t o that expected over the ocean, although some minor increase i n

evaporation occurs in the increased wind flow diverted about the mountains.

(3x1 the central isthmus, high sunlight and wind flow channeled between the

two muntain masses causes evaporation t o increase 10 t o 20% above that for

the ocean with summer evaporation greater than 10 in./mo.

Neither sunlight nor evaporation measurements were available for the

windward or southeastern flanks of HaleakalB.

TABLE 6. STATION NUMBEX, PERIOD OF RECORD, !@XVRED EVAPORATION, PAN TYPE, AND AIXTUSED EVAPORATION FOR M3UI

PEZ SIZITION PAN DESCRIPTION FACJDR ARJ. Eleva- Other

EX*. CcanFo- Paint tion Sun- ANNUAL* NUMBm RECORD (in.) s i t ion Notes Pan l iqh t (in./yr)

.... .... 296.10 1982 ..... galv. Al 5 f t .... 310.00 1960-62 91.94 galv. Al surf. 1.03 0.98 96.6

1980 s. steel 5 f t

310.10 1962-83 97.37 galv. s. s tee l Al 5 f t 0.97 0.98 96.4

galv. s. s tee l

galv. s. steel galv.

s. s tee l

galv. s. steel s. steel

galv.

galv.

Al surf.

Al 5 f t

Al surf.

5 f t

Al surf. 5 f t

5 f t

A l surf.

Al

%~djus ted annual = measured annual x pan correction i sunlight correction.

TABLE 6 4 o n t i n u e d

PERIOD ANNUAL STATION OF PAN DESCRIPTION FAerOR Aaf. Eleva- Other Paint tion Sun- mAl,

NUMBER RECORD (in.) s i t i o n Notes Pan l i g h t (in./yr)

316.30 1966-67 76.75 galv. A l sur f . 1.08 1.05 78.8

317.10 1958-60 85.82 galv. Al s u r f . 1.08 1.05 88.3

317.20 ............ galv. Al surf . .... .... .... 1960-77 87.48 s. steel 5 f t 1.03 1.04 86.6

321 -50 1967-83 91.90 s. steel 5 ft 0.97 0.99 90.0

361.00 ............ galv. Al surf . 1963-82 81.16 galv. A l 5 ft

363.10 1963-71 77.83 galv. Al surf .

372.20 1970-71 81.95 galv. Al 5 f t

372.30 1964-70 79.51 galv. Al surf .

373.00 1982 ..... s. steel 5 f t

385.00 1976-83 78.47 galv. A l 5 f t

388.00 1976-83 71.87 galv. Al 5 f t

391.10 1976-83 95.28 galv. Al 5 f t

391.20 1982-83 94.91 galv. Al 5 f t

393.00 1974-83 96.72 s. steel 5 f t

394-00 ....... 97.74 galv. Al surf . 1964-83 s. steel 5 f t

394.10 ............ galv. Al surf . 1966-83 97.49 s. steel. 5 f t

3% .OO ............ galv. surf . 1960-83 94.03 s. steel 5 f t


401.10 ............ galv. Al surf . 1966-83 84 -20 s. s t e e l 5 f t

..... 402.00 1971-72 s. steel 5 f t

403.10 ............ galv. surf . 1966-83 94.20 s. steel 5 f t

404.10 1 x 2 6 6 94.7 galv. A l

404.30 1962-83 93.90 galv. Al surf . 1.08 1.05 % .6


406 -30 1982-83 ..... s. steel 5 f t 0.97 0.91 .... 410.10 ............ galv. Al surf .

1%6-83 97.03 s. steel 5 f t

W L E 6 4 o n t inued --- - - - . -- -- d

PERIOD ANNUAL SIlATION PAN DESCRIPTION FACIOR AAS.

NUMBER Eleva- Other mm. Paint tion Notes Sun- ANNUAL F R D -- !@,I- _ _ s i t i o n pan l i q h t (in./yr)

.... .... .... 413 .OO 1960-83 ..... galv. A l surf . 82.79 s. steel 5 f t 1.03 0.98 87 .O

413.20 1957-60 82.79 galv. A l surf canopy 0.97 1.05 76.5

.... ........ 415.00 1963-83 93.23 galv. Al surf s. steel 5 f t 1.03 0.98 98.0

416 .OO 1971-83 83.52 s. steel 5 f t 0.97 0.95 86.9

419.00 1977-83 88.21 S. steel 5 f t 0.97 0.94 91.0

....I.... .... 457.00 1963-82 91.97 galv. Al surf . s. steel 5 f t 1.03 0.98 96.7

458 -00 1963-65, 103 -01 1980 galv. Al surf . 1.08 1.03 108.0

........ 458.10 1964-71 ..... galv. Al surf . .... 1982 82.35 s. steel 5 f t 1.03 0.98 86.6

........ .... 462.00 1982 ..... galv. Al 5 f t

462.10 1964-67 73.3 galv. Al surf. 1-08 1.04 76-1

.......I .... 463.20 1965-67 ..... galv. A l surf .

466.10 1963-64 105.91 galv. Al surf . 0.88 1.04 89.6

484.10 1976-83 68.01 galv. Al 5 f t 0.97 0.94 70.2

485.00 1962-71 94.04 galv. Al surf . 1.08 1.03 98.6

485.10 1963-66 83.19 galv. Al surf . 1.08 1.03 87.2

485.30 1960-66 76.45 galv. Al surf . 1.08 1.04 79.4

486.50 1977-83 79.67 s. steel 5 f t 0.97 0.97 79.7

486.60 1971-77 105.54 s. steel 5 f t 0.97 0.94 108.9

Pan and sunlight measurements on the windward coasts were used t o set

evaporation values (Table 7; Figs. 20, 21) , but measurements on the leeward areas and the central mountain masses were not available. The massive moun- ta in masses of Mauna Kea and Mauna Loa reach w e l l above the tradewind inversion and s e t up unique patterns of cloud and wind flaw.

The bow wave and nocturnal downslope flaw from the major mountains directly oppose the trade winds on the windward coasts, and l ight winds and reduced sunlight combine t o cut evaporation along the coast t o 75% that of the ocean and t o 25% of the ocean value in the inland maximum rainfall zone.

Monthly values are nearly constant throughout the year. A t 5000 ft, increased mixing of dry a i r fram above the inversion and re-

duced cloudiness cause evaporation again t o increase t o about 33% tha t of the ocean. The single Wemat ion s i t e in the clear, dry a i r above the inversion near the Mauna Kea crest suggests that evaporation increases t o 50% more than

surface oceanic rates.

On the southern slopes of Mauna Lua near PZhala, upslope flaw of the trade winds £om orographic clouds which reduce evaporation t o 75% tha t of the ocean nearby and causes nearly constant monthly rates of evaporation.

Wind flaw diverted through the Mauna Kea-Kohala saddle a t f i r s t increases evaporation about 10% near the coast, but cloudiness and higher elevation

inland reduce evaporation t o 50% tha t of oceanic. As the wind exi t s the saddle area, evaporation increases t o 75% tha t of oceanic a t W a i m e a . Further

t o the lee aver the dry, dark barren lava flaws, annual rates are a s great as 50% above the oceanic with summer values greater than 12 in./m and wen

winter values more than 6 in./mo.

Increased wind flow about the northern t i p of the island causes a 20%

increase i n evaporation above the oceanic.

On the sheltered l e e slopes, complex land-sea breeze wind regimes cause clouds, and l ight wind flaw is about 40% tha t of the oceanic values beneath the clouds, but increase again with elevation where dry a i r is mixed from above the inversion.

TABLE 7. SCATION NUMBER, PERIGD OF RECORD, PEASUED EVBPORATION, PAN TYPE, AND ADJUSTEI) EWAl?ORA!l!ION FOR HMAI" I ISLAND

PAN D-ION FACrOR

11.00 1962-72 52.21 galv. Al surf . 1.08 1.02 55.3

12.14 1962-64 67.72 galv. Al surf.

13.00 1962-73 63.30 galv. Al surf .

14.00 1962-73 73.89 galv. Al surf . 1.08 1.02 78.3

21.00 1931-45 63.31 galv. surf . 1.0 1.0 63.3

87.00 1955-68 65.89 monel surf . 1.0 1.05 62.8

89.50 1963-66 45.18 galv. Al surf . 1.08 1.04 46.9


. . . . ......... 95.60 1975-76 108.0" wash tub surf .

160.00 1960-71 95.36 galv. Al. surf . 1.08 1.0 103.0

161.00 1961-71 81.66 galv. Al surf .

166.00 1968-71 92.37 s. steel 5 f t

168.00 1963-75 83.22 galv. Al surf . 1.08 0.99 90.8

171.00 1962-63 92.86 galv. Al surf . 1.08 1.06 94.6

173.00 1960-63 74.65 galv. Al surf . 1.08 1.06 76.1

176.00 1961-71 74.54 galv. Al surf . 1.08 1.0 80.1

179.00 1962-67 82.02 galv. Al surf . 1.08 1.0 88.6

179.10 1966-71 82.23 galv. Al surf . 1.08 1.0 88.8

182.00 1962-65 66.06 galv. Al surf . 1.08 1.05 67.9

191.10 1976-84 64.41 s. steel 5 E t 0.97 1.0 62.5

201.20 1967-69 41.02 galv. surf . 1.0 1.0 41.0

203.20 1977-84 44.58 galv. surf . 1.0 0.95 42.4

206.00 1963-64 79.91 galv. Al surf . 1.08 1.03 83.8

211.10 1961-64 57.01 galv. Al surf. 1.08 1.05 58.6

213.00 ............ galv. Al surf . . . . . . . . . . . . . 1963-83 88.44 galv. white 5 f t 1.08 0.98 97.5

213 -10 ............ galv. Al surf . 1964-83 80.96 s. steel 6 f t

214.10 196164 72.30 galv. Al surf. 1.08 1.05 74.4

215.30 1964-83 61.74 s. steel Al surf . 0.97 0.99 60.5

'Estimated. +Adjusted annual = measured annual x pan correct ion i sunlight correction.

PERIOD ANNUAL m I O N PAN D ~ C R I P T I O N FACrClR AAT. Eleve Other m. Paint tion sun- ANNUAL

NIW3m RECORD (in.) s i t i o n Notes Pan l i q h t (in./yr)

215.40 196163 ... . . galv. Al surf .

216.30 196265 53.47 galv. Al surf.

216.40 1962-70 69.9 galv. Al surf . 1 -08 1.04 72.6

U6.50 1964-70 70.45 galv. Al surf .

217.00 1966-68 79.98 galv. Al surf .

218.00 1974-83 75.64 galv. A l 6 f t

218.20 1973-83 86.8 galv. Al surf.

220.00 1962-70 68.81 galv. A l surf . 1-08 1.0 74.3

220.40 1960 ..... galv. Al 5 f t

220.50 1962-70 79.91 galv. Al surf.

221 -30 . , , , . . , . , . . . galv, AJ. surf, 1964-82 79.79 s. steel 6 f t

HA WAI'I

Ka Loe A J.O. Juvik tronsect points

0 10 20 M i l e s - 0 10 20 30 Kilometers

Figure 20. Adjusted annual pan evaporation for Hawai'i Island

Mauna Kea

Sta. 168.00

HAWAI'I N

Jon. June Dec.

Kealokekua

J a n . J u n e D e c .

J o n . J u n e D e c .

J a n . J u n e D e c .

J o n . J u n e D e c .

UHM-WRRC

Mauna Loo

Figure 21. Pattern of mnthly pan evaporation for selected stations, Hawaili Island

USE OF PAN EVAFORATION REQORlXS

The series of maps showing the distribution of pan evaporation rates

should be interpreted and util ized with care. It is necessary t o understand differences (1) between evaporation and transpiration, and (2) i n energy budget and aerodynamic properties between evaporation pan and vegetated surfaces.

The transpiration process may be physically described i n terms of a

resistance t o a diffusive and turbulent vapor flux i n the external air--a similar diffusive resistance that results from the internal leaf geometry, in- cluding stomata and, parallel t o the l a t t e r , a resistance t o vapor diffusion

through the cuticle. In contrast, the l a s t two resistances do not exis t i n the f ree water evaporation.

Reservoir

The rat io of reservoir t o pan evaporation is called the pan coefficient. Kohler, Nordenson, and Fox (1955) have presented a map of the average annudl

C l a s s A pan coefficient over the U. S. Values range from less than 0 -60 in the Imperial Valley of California t o more than 0.80 w e r the northern Great Lakes

and i n eastern Maine. They have cautioned that these values a re unlikely t o be within 10% accuracy for annual values and should never be used tor esti-

mates of monthly values in a climate of pronounced seasonal variation. The relationship between reservoir and pan evaporation is basically

dependent on three factors: the vapor transfer coefficient; the saturation vapor pressure, or the temperature of the water surface; and the vapor

pressure of the overlying air . For a given wind speed, the vapor transfer coefficient increases with the roughness of the surface, which is determined by the nature of the surrounding terrain i n the case of reservoirs and by the height of the pan rim in the case of an evaporation pan.

The saturation vapor pressure is a function of the water temperature. In mid-latitude the large heat storage of a reservoir, in commrison with a pan, greatly affects their relationship from one season t o another. In the humid tropics, a i r and shallow-water temperatures do not differ greatly, while res-

ervoir surface temperature is mewhat lcwer. In humid regions vapor pressure of the a i r is likely t o be the same over mall and large water surfaces, Therefore, the evaporation pan is likely t o be a more accurate estimator of

reservoir evaporation i n Hawai'i than i n most other p r t s of the U.S. and the

pan coefficient is probably in the neighborhood of 0.8.

Crops

With due caution, the use of evaporation pans t o estimate crop water use

for periods of a week or longer is warranted and widely practiced. Doorenbos

and Prui t t (1975) have suggested that potential evapotranspiration, or also

known as reference crop evapotranspiration (ETo) in their terminology, can be

related t o pan evaporation by the pan coefficient (%) as

Doorenbos and Prui t t (1975) have reviewed many studies of pan coeffi-

cients and expressed the average values a s a function of relative humidity and

wind speed.

In lowland areas of Hawait i below the tradewind inversion, relative

humidity exceeds 70% and wind speed is moderate. In high mountains above the

inversion layer, relative humidity is lcw and wind speed can be moderate t o

strong (Mendonca 1969) . The definition of potential maptranspiration, or ETo, is very precise.

It refers t o the rate of evapotranspiration £ram an extended surface of short,

green grass cover of uniform height, actively growing, completely shading the

ground, and not short of water. Therefore, even when the water supply is

adequate, evapotranspiration from a tall, rough crop surface or during the

ripening stage when the crop is not actively grwing may depart f r m the potential rate. me ra t io between crop evapotranspiration and the reference

crop evapotranspiration is known as the crop coefficient, Kc. Doorenbos and

Prui t t (1975) have summarized crop caefficients for many crops.

The apprcach by Doorenbos and Prui t t (1975) consists of two steps:

(1) an estimation of potential evapotranspiration, or reference crop evapo-

transpiration f r m pan evaporation under various climatic conditions; and

(2) an estimation of crop evapotranspiration for any species and stage of

developnent by the crop coefficient.

Use t o pan ratios have been measured for several crops i n Hawai'i.

During the f i r s t f ive months from germination t o the establishment of a full

canopy of sugarcane, the ra t io (a t can= level) increases from 0.40 t o 1.01

(Jones 1980). After the establishment of fu l l canom, the ra t io reaches

a peak of 1.20 a t 1 0 mo and then declines gradually t o 0.98 a t 17 mo. Ebr

furrow- or sprinkler-irrigated mature sugarcane, the ra t io is 1 , O w i t h a surface pan, Dripirrigated cane uses an average 0-8 of the annual surface pan evaporation or 0.7 of the pan elevated t o 5 f t (1.52 rn) height, about 15%

less than sprinkler- or furrw-irrigated cane. Evapotranspiration by Bermudagrass is essentially the same a s C l a s s A pan

evaporation when soil moisture s t ress is small (Ekern 1%6a). As the s o i l moisture s t ress increases, the grass sod M n t a i n s high rates of water use unt i l the soil moisture s t ress exceeds 1 bar, but is unable t o maintain these rates as tfre soi l nroisture stress increases toward the 15-bar level.

Pineapple evapotranspiration rate is only one-f ifth tha t of pan evaporation (Ekern 1965~). The greatly reduced transpiration rate is largely due t o

daytime suppression of water vapor exchange by the pineapple leaf. Lettuce

and Chinese cabbage i n the winter season has a pan ra t io of 1.0. Under dr ip irrigation the pan rat io is about 0.60 for lettuce, and between 0 -70 and 0.80

for Chinese cabbage (Wu 197 2) . Evaporation f ram Law Humic Latosols (Oxisols) in Hawai' i a t f ie ld mois-

ture content is only one-third the rate from a pan (Ekern 1966b). Similar low evaporation rates have also been reported for tropical so i l s i n Puerto Rico.

Measurements of pan evaporation in Hawai'i began i n 1894 and eventually included intermittent observations for aver 200 sites. Most s i t e s had standard, galvanized Class A pans on the surface, but many were l a t e r replaced with stainless s teel pans t o avoid corrosion and set on 5 f t high platforms. Sites w e r e concentrated i n the dry lowland areas s i n e measurements were used

t o schedule crop irrigation. Crop water use measured w i t h lysimeters was util ized t o develop empirical relationships between pan evaporation and actual

crop evapotranspiration. &all, rain-shielded evaporimeters have extended evaporation measurements into the high rainfal l areas.

Tables of mnthly and annual values of evaporation were assembled and the

standard deviation from the mean determined. Maps of annual evaporation were prepared for each of the four major islands from pan values adjusted for sun-

l ight, pan compsition, and elevation t o represent an equivalent evaporation from a galvanized pan a t the surface.

The standard deviation decreased from nearly 30% of the mean for daily

observation, but only 15% for monthly and 7% of the mean for annual values and

the distribution of pan evaporation from the records of longer duration

approached normality . EXlpirical relationships bemeen evaporation and more readily available

meteorological data, such as temperature and rainfall, were explored and found

t o have limited amlication even for the longer term annual evaporation rates. The pattern of annual evaporation for the islands differs from the equi-

librium value of 80 in./yr produced by the long fetch of the trade winds over

the ocean a s the pattern of cloudiness, sunlight, and rainfal l changes in response t o wind flow over the island topography, Evaporation on the windward coasts is much the same as that over the ocean, except where the massive bulk of Mauna Loa and Mauna Kea blocks the tradewind flow and reduces evaporation on the windward mast of Hawai'i Island 10 t o 20% belaw that wer the ocean,

A s the trade winds m e onshore, the orographic cloud which forms causes

evaporation t o decrease rapidly inland t o less than 30% of the oceanic rate.

Beneath th i s persistent summer cloud, monthly evaporation rates remain nearly

constant throughout the year, Evaporation increases 10 t o 20% where winds increase around the ends of the islands or in saddles between the mountains

where cloudiness was not great, Summer evaporation rates are greater than 1 2 in,/mo on the dry leeward coastal plains where p s i t i v e advection of heat increases annual pan evaporation rates 30 t o 40% above those over the nearby ocean. Only in the leeward Kona area of Hawai'i Island is the sea-breeze

cloud sufficient t o reduce evaporation, The i n i t i a l decrease i n evaporation w i t h an increase i n elevation changes in the dry, sunny and wlrx3y s i t e s above the tradewind inversion, and evaporation above the 6000-ft elevation on the high wuntain slopes increases t o again equdl or to exceed rates near sea

level,

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APPrnIX cxlKmms Tables

. . . . . . . . . . . . . . . A.1. Locations of Pan Evaporation Stations 63

A.2. AlternateStationNames . . . . . . . . . . . . . . . . . . . . . . 70

A.3. Alphabetical L i s t of Current Station Names . . . . . . . . . . . . . 73

. . . . . B.1. Pan Evaporation Reasurements. State of Hawai'i. 1910-1983 80

B.2. Monthly and Annual Pan Evaporation Statist ics. State of Hawai'i . . 129 Figures

A.1. Location Map of Pan Evaporation Stations. LZhali . . . . . . . . . . 75

A.2. Location Hap of Pan Evaporation Stationc. Molokati . . . . . . . . . 75

A.3. Location Map of Pan Evaporation Station. O'&u . . . . . . . . . . . 76

A.4. Location Map of Pan Etraporation Station. Kaua'i . . . . . . . . . . 77 A.5. Location Napof Pan Evaporation Station. Naui . . . . . . . . . . . 78

A.6. Location &p of Pan Evaporation Station. W a i t i Island . . . . . . 79

APPENDIX TAl3LE A.l. WCATIONS OF' PAN EVAPORATION STATIONS, S T m OF HAWAI'I

sT.ATE WS STATION NAPE OBSHIVER PERIOD OF FULL EL. COORDINATES KEY NO. NO. RMX>RD YRS ( f t ) Latitude Longitude

Makino Field 700" Waiubata Naalehu Pahala Hilo Airport Arnauulu Camp 4* Hawaii Sub Off * W a i koloa Sta t ion 3* Stat ion 3 t Puakea* Stat ion 14* Haw i* Stat ion 5* Stat ion 16" Kohala Maulili* Niulii* Kohala Stat ion 12* Lalanil0 Fld Off Mealani Farm Puu Pulehu Res Kukui hael e Landg* Honokaa Pasture Kawel a New Stable* Field 34-35 Ahualoa* Field 26 A i p r t PMA Plant

HIWAI'I 1-

Kau Sugar 196 2-197 2 Hutchinson Sug 1 % 2-1 96 4 Kau Sugar 1962-1973 Kau Sugar 1962-1973 Kau Sugar 1931-1945 N a t l Weath ~ e r v ? 1955-1968 Hilo Sugar 1 96 3-1 966 HSPA 1963-1983 UH-WRRC? 197 5-197 6 Kohala Sugar 1960-197 1 Kohala Sugar 1965-1966 Parker Ranch 1961-1971 Kohala Sugar 196 8-1971 Kohala sugar? 1963-1975 Kohala Sugar 1962-1963 Kohala Sugar 1960-1963 Kohala Sugar 1961-1971 Kohala Sugar 1962-1967 Kohala Sugar 1966-1971 Kohala Sugar 1962-1965 IXBrALD 1976-1984 UH- WITAHR? 1967-1969 l2mmLD 1977-1984 Hamakua sugar? 1963-1964 Honokaa Sugar 1961-1964 Hamakua sugar+ 1963-1983 Honokaa Sugar 1964-1983 Honokaa Sugar 1961-1964 Honokaa Sugar 196 4-1983 Honokaa Sugar 1961-1963 Harnakua sugar$ 1962-1965 Hamakua sugar? 196 2-1 97 0

*See Alternate Names List . tgnall pin; same site as 160.00. ?Revised, w a

APPENDIX TABLE A. 1 .--Continued a\ .h -

STATE NWS STATION NAME OBSWER PERIOD OF FULLI EL. COORDINATES KEY NO. NO. RECORD YRS ( f t) Latitude Lonuitude

Field 003 7 204 paauhaut

Harnakua Mill* Field 328*

.oo PNA

.40 Field 14 220.50 Field 015 221 -30 Hamakua Makai*

Paauhau Sugar Hamakua sugart Hmakua sugart Hmakua sugart Paauhau Sugar Paauhau Sugar Paauhau Sugar HSPA

MAUI lxxAlm

296 . l o Olawalu* Pioneer Mill 1982 310 -00 Field 906 Vil 7* HC&S? 1960-1962;

1980 310 . lo Field 906 HC&S 1962-1983 310.20 Field 906-2 HC&S 1964-1966 313 -00 0260 Field 811 Vil 3" HC&S 1963-1 983 313 . lo Field 815 HC&S 1960-1963 313 -30 Field 821 HC&S 197 1-1983 314 .OO Reservoir 81* HC&S 1960-1961;

1976-1981 314 . l o Field 412 HC&S 1972-1983 316 -00 Field 405* HC&S 1960-1961 316 -20 Field 405 HSPA 1957-1960 316.30 Field 404 HC&S 1966-1967 317 . lo Field 408 M I * HSPA 1958-1960 317 -20 Field 413 HC&S 196 0-1977 3 2 -50 Field 402 HC&S 1967-1983 361.00 5177 Lahaina* Pioneer M i l l 1963-1982 363 . lo Field F-2* Pioneer Mill 1963-1971 372.20 Field MB-7 Pioneer Mill 1970-1971 372.30 Field MG-9* Pioneer Mill 1964-1970 373 .OO Field LA-5* Pioneer Mill 1982 385 -00 Field 55* Wailuku Sugar 1976-1983

*See Alternate Names List. t Revised. f~omer observer, HSPA.

APPENDIX TmLE A. 1 .---Continued

STATE I'b7S STATION NAME OBSERVER PERIOD OF RILL EL. 030RDIWB Krm NO. NO. REXDRI) YRS (ft) Latitude Longitude

388.00 Field 72 Wailuku Sugar 1976-1983 391.10 Field 95* Wailuku Sugar 1976-1983 391.20 Fie ld 201 Wailuku Sugar 1982-1983 393 -00 Fie ld 719 HC&S 1974-1983 394 -00 Village 6* HC&S 1964-1983 394 . lo Field 911* HC&S 1966-1983 396.00 8543 Puunene* HC&S 1960-1983 401 .OO Village 13" HCCS 196 2-1 983 401 . lo F ie ld 809 HC&S 1966-1983 402.00 0280 Village lo* HC&S 1971-1972 403 . l o Field 601 HCsS 1966-1983 404.10 Fie ld 603* HC&S 1962-1966 404.30 Field 604 HC&S 1962-1966;

197 1-1 983 404 -40 Fie ld 604B HC&S 1966-1970 404.50 Fie ld 806-2 HC&S 1964 406.20 Field 211* HCsS 1964 406.30 Field 116 HC&S 1982-1983 410 -10 Fie ld 502 HC&S 1966-1983 413 .OO Kaheka* HC&S 196 0-1 983 413.20 Field 205 HSPA 1957-1960 415.00 Field 306* HC&S 1963-1983 416 -00 Field 102" HCS 1971-1983 419.00 Field 301 HC&S 1977-1983 457 .OO 8398 Puukol ii* Pioneer Mill 1963-1966 ;

1980-1982 458.00 Kahana Camp* Pioneer Mill 1963-1965;

1980 458.10 Field 31-C* Pioneer Mill 1964-1971;

1982 462.00 Field 32-A* Pioneer Mill 1982 462 . lo Field 24 Pioneer Mill 1%4-1967 463 -20 Field A-4* Pioneer Mill 1965-1967 466 -10 30 Lua Mauka* Pioneer Mill 1963-1964

*See Alternate Names list. t~onner observer, Maui Pine.

= = - coob * O N

APPENDIX TABLE A.l.--Continued

s- Nws STATION NAME OBSWm PERIOD QF FULL, EL. C03RDINATFS KEY NO. RMX)RD YRS ( f t ) Latitude Longitude

752 -00 Waipio HSPA/Oahu Sugar

752.50 Waipio Field L HSPA 756.00 0100 Field 610* Oahu Sugar 761 .lo Field 615 Oahu Sugar 772 -60 Moandlua UGS 782 -00 5637 Lower Luakaha* BhS 783 .OO 6928 Nuuanu Reservoir 4* BhS 787.00 6228W Maunawili Ranch Kaneohe Ranch 787.10 6222 M a u n a w i l i HSPA 795.10 9523 WaimanaloExpSta UEB-HITAHR~ 798.00 9231 Waianae* Capital Investment 813 -00 1527W Robinson Camp l* Hzwaiian Pine 815 -00 Field 245" Oahu Sugar 816 -20 Mililani WrP* UH-WRRC 816 -30 Benchmar k-Waipio* UH-HITAHR~ 818.10 Field 220 Oahu Sugar 820 -20 8172 PIiI Wahiawa* PRI 824 .lo Field 525 Oahu Sugar 825 -30 Field 541* Oahu Sugar 826 -00 Stat ion 4101* Dole Corp 830 -30 K o a Ridge* UH-WRRC~ 841.00 3734 K a w a i h a p a i Waialua Ag 841 -10 Kawa i hapai Waialua Ag 846 -00 Ranch Waialua Ag 847.00 9195 Waialua* Waialua Ag 851 -00 Kemoo 3* Waialua Ag 854 -00 H e l e m m 9 Waialua Ag 856 -10 Burma Road* Dole Corp 860 -60 Helemano 13 ~ a i a l u a ~~f

861 .OO Opaeula 17* Waialua Ag 882 -10 North Fork* USSS 890 -00 3754 Kawailoa 4* Waialua Ag 892 -00 9593 Waimea 3* Waialua Ag

*See Alternate Names list. t ~ e v i s e d .

APPENDIX TABLE A.l.--Continued

STN'E NWS STATION NAME OBSWW PERIOD OF FULL EL. KEYNO. NO. RECORD YRS (ft)

894.20 Kawailoa 20 Wkai* Waialua Ag 1962-1964 0 840 908.00 Pump 4* Kahuku Plant ' n 1960-1965 0 40

KAUA' I ISLAND

925.00 Field 130* Olokele Sugar 1961-1975 7 135 927 .OO 0470 Eleele McBryde Sugar 1963-1968; 5 165

1981-1983 0 930.00 8941 Wahiawa* McBryde Sugar 1960-1983 15 215 931.00 9955 West Lawai* McBryde Sugar 1960-1983 5 210 934.00 0456 Ehst Lawai* McBryde Sugar 1964-1983 11 440 935.00 4950 Kukuiula* McBryde Sugar 196 3-1983 3 105 935.10 Paanau (McB ryde McBryde Sugar 1964-1968 2 135 936.00 4742 Koloa McBryde Sugar 1910-1 911 1 240 940.00 8352 Puuhi* McBryde Sugar 1960-1983 19 80 941.00 5710 Mhaulepu* McBryde Sugar 1960-1983 19 100 943.00 9253 Waiawa Kekaha Sugar 1910-1 911 1 10 943.20 Field 25 Kekaha Sugar 1961-1962 1 400 944.00 4272 Kekaha Kekaha Sugar 196 0-1983 9 10 945.00 2161 Hukipo Kekaha Sugar 196 2-1983 2 800 962.00 Field 30* Olokele Sugar 1963-1975 7 110 965.00 5864 Makaweli* Olokele Sugar 196 9-197 0 1 140 965.10 Field 070 Olokele Sugar 1971-1975 6 140 966 .OO Field 360" Olokele Sugar 1961-1975 6 470 981.00 Field 370* Olokele Sugar 1963-1975 9 350 982.00 Field 540 Olokele Sugar 196 5-197 5 6 775 986 . lo McBryde Var Sta* HSPA 1960-1983 16 6 30 993 .OO Field 612* McBryde Sugar 1961-1983 11 500 994.00 4750 Koloa Mauka* MCB- sugart 1976-1983 0 640

1004 .OO 8573 Reservoir 6* Grove Farm 1961-1983 11 420 1005 .OO 3023 Kaluahonu* Grove Farm 1961-1983 14 330 1006.00 1038 Halenanahu* Lihue Plantation 1961-1983 13 4 90 1011.00 8570 LP Reservoir 5* Lihue Plantation 1960-1983 14 3 85 1013.20 Field L-l* Lihue Plantation 1968-1975 6 3 40

*See Alternate Names list. t ~ r o v e Farm former observer.

CR c.2

COORDINATES Latitude Lonqitude

21'35 '45" 158'02'00" 21'41 '42" 158'00 '12"

SllATE WS STATION NAME OBSWER PERIOD OF FULL, EL. OIWES KEY NO. NO. RECORD YRS (ft) Lati tude Longitude

F ie ld L-3A F ie ld L-4 LP H I 4*

5580 Lihue Airport* F ie ld L-24"

6082 Mana* L h d o a

4735 Kolo* 6850 Niu Ridge*

Lihue P lan ta t ion Lihue P lan ta t ion Lihue P lan ta t ion Lihue P lan ta t ion Lihue P lan ta t ion Kekaha Sugar Kekaha Sugar Kekaha Sugar Kekaha Sugar

1040 .OO 8205 Puehu Ridge* Kekaha Sugar 1061 .OO E3KW 5* Lihue P lan ta t ion 1061.30 F i e ld H-46' Lihue P lan ta t ion 1062.10 5560 Lihue Variety Sta* Lihue P lan ta t ion 1062.20 F ie ld 38-A* Lihue P lan ta t ion 1062.30 F ie ld H-32!* Lihue P lan ta t ion 1064.30 H 23 Camp 9 Lihue P lan ta t ion 1066 .OO F ie ld Mkee 3C* Lihue P lan ta t ion 1072.10 Puu Lua USSS 1082.00 9130 Waiakoali Camp* USGS 1092.00 3104 Kaneha Reservoir* Lihue P lan ta t ion 1101 . lo Spdlding Monument* Lihue P lan ta t ion 1102 .OO F ie ld W2B* Lihue P lan ta t ion 1104.20 F i e ld M-19* Lihue P lan ta t ion 1110.00 0935 F i e ld M-8* Lihue P lan ta t ion 1112.00 3982 Kealia Lihue P lan ta t ion 1114.00 0145 Fie ld M-14A* Lihue P lan ta t ion 113 4.00 4561 Kilauea* N. Rapozo 1135.00 4566 Kilauea Fie ld 17* Kilauea Sugar 1136.00 F i e ld 23 Kilauea Sugar 1141.20 F ie ld 29 Kilauea Sugar 1143 .OO F ie ld 30" Kilauea Sugar 1145 .OO 6529 Moloaa ~ u u a u a u ~ T. Java1 iena 1146 .OO Puuauau Lihue P lan ta t ion 1147 .OO F ld 960 Moloaa Lihue P lan ta t ion

*See Al te rna te Names list. T ~ w s ta t i on .

Sta te Key No.

APPENDIX TABLE A, 2. AL- S I W I O N NAPES

Stat ion Name Alternate Names and Notes

Field 700 Anaauulu Camp 4 Hawaii Sub O f f

Stat ion 3 Puakea Stat ion 14 H a w i Stat ion 5 Stat ion 16 Kohala Maulili Niuli i Stat ion 12 Kukuihaele Landg New Stable Ahualoa Paauhau Hamakua Mill Field 328 Hamakua Makai

Olowalu Field 906 Vil 7

Field 811 V i l 3 Reservoir 81 Field 405 Field 408 MAS1 Lahaina Field F-2 Field LA-5 Field 55 Field 95 Village 6 F i e l d 911 Puunene Village 13 Field 809 Village 10 Field 603 Maui Pine Kaheka Field 306 Field 102 Puukolii Kahana Camp Field 31-C Field 32-A Fie ld A-4

II;AWAI'I Field 712 Substation Mauka, Hawai i Sub-Station Hilo Mauka Substation Makai, Hawaii Sub-Station Hilo Makai, Ag Office Q o l u 5 Puakea Puumano, Puakea Ranch Hoea, Hoea Mill Hawi Office, Stat ion 1 Alaalae, Alaalae 2 & 3 Union Mill, Union Park Maulili, Kohala Mauka, Stat ion 11 Niuli i Camp, Stat ion 13 Waiapka, Niul i i 15, Waiapuka Weir Kukuihaele M i l l Field 288 Field 7A Office, Paauhau Office Hamakua Sugar Field 28 Hamakua Variety Station, Variety Stat ion

mu1 Field 935, Field 12, Stat ion 12 Field 913, Camp malea, Reservoir 9, Camp 7 V i l 7 , Field 906 Field 811, Camp K3, Kihei Camp 3, Kihei Vi l 3 Field 408 Stat ion 6 Field 408 Main Office, Stat ion 17 Field 72 Field 610, Stat ion 16, LA 5, Moo 17 Field 36 Field 98 Field 903, Field 902, Camp 6 F i e l d 900 Field 713, Puunene M i l l Field 806, Field 3 Village 13, Camp 13 Field 510, Camp 10 mn?p9 Field 211 Field 205 Field 304, Field 77, Stat ion 4 Fie ld 101, 8, 10; Stat ion 1 Field C3, Field 325, Stat ion 10 Stat ion 12, Field 425, Field 32-B, No. 12 Field 32, Field 150, Stat ion 04 Field 31-A, Field 440, Stat ion 13, Pedro Camp ES8

A J ? P N I X TABLE A, 2--Cant inued

S t a t e Kev No. Stat ion Name Alternate Names and Notes

30 Lua Mauka Hamakuapko

US Magnetic Obs Observatory Keeawku

munp 10 Field 18 Kunia Eha M i l l Waipio Field 610 Lower Luakaha Nuuanu Reservoir 4 Waianae Robinson Camp 1 Field 245 Field 245 PRI Wahiawa

Fie ld 541 Sta t ion 4101 Koa Ridge Waialua Kemoo Helemano 9 Burma Road Cpieula 17 North Fork

Kawailoa 4 W a i m e a 3 Kawailoa 20 Makai -4

Eleele Wahiawa W e s t Lawai East Lawai Kukuiula Puuhi Mahaulepu Fie ld 30 Makawel i Fie ld 360 Fie ld 370 McBryde Var Sta Fie ld 612

Field 30A Field 103 (mved from No. 485.2)

0' AHU US Magnetic Observatory 1 US Magnetic Observatory 2 HSPA Experiment Stat ion, HSPA Makiki, ESrperiment Sta t ion Reservoir 10 Fie ld 200, Field 18 (Oahu Sugar) Kunia Sub-Station EMa Plantation HSPA Waipio, Waipio Substation Field 260, Field 615, Waimalu Field 605 Luakaha Lower, W a h a Nuuanu, Nuuanu Dam 4 , Upper Luakaha Waianae Mill (relocated 1969) Robinson I, Hoaeae Upper, Field 4303-4 (Dole) Fie ld 53 Fie ld 23 (moved 1962) PRI Waipio, Waipio Main Station, PRI Wahiawa Main Sta t ion Aiea Field 42 Sta t ion 4101-2, Field 42 (Omhu Sugar) Gage 1 Mink Waialua Mill, Waialua (Of f ice) , Off ice K e n m 5, Kemoo Camp 5 Helemano Camp 9 Helemano 6C; (unknown location) Opaeula 8 , Opaeula Camp 8 North Fork Kaukonahua (11501, N Fork, Kaukonahua Transpiration S i t e , North Fork Kaukonahua Kawailoa 3 Waimea, Waimea 9, Kawailoa Camp 9 Kawailoa 20 Pmp A, Pump 4 (Kahuku Plantation)

KAUA' I Field 216 Office Wahiawa, Field 112 Lawai West, Field 410 Fie ld 504 Koloa (Kukuiula) , Field 516 K 2 PuhJ, Field 74, K 2 K 2 l Mahaulepu, Fie ld 728, Fie ld 030, Field 3 Off i c e Makaweli F ie ld 36 Field 37 Field 306 Puuohewa

Sta te Key No. Sta t ion Name Alternate Names and Notes

Reservoir 6 Kaluahonu Halenanahu LP Reservoir 5 Field L-1 LP H I 4

Lihue Airport Field L-24 Mana Niu Ridge Puu Opae Kolo Niu Ridge Puehu Ridge Em75 Fie ld H-46 Lihue Variety Sta Fie ld 38-A Fie ld H-32A Fie ld Makee 3C Waiakoali Camp Kaneha Reservoir SpClding Monument Fie ld M-2B Fie ld M-19A Fie ld M-8 Field M-14A Kilauea Kilauea Field 17 Field 29 Field 30 lbloloaa Puuauau

Fld 960-Moloaa

Wilcox Ditech (former observer, Grove Farm) , Fie ld 600 Fie ld 31, F ie ld 814 Kalauhonu, Field 710 Halenanaho, Field 25 H22 Reservoir 5, Field 22-A, H I 19, H I 19A Ll , L3A Fie ld H-4AI Gage 4-A (moved 1970) H4, Field 4-A, H4-B, HI-4B Airport F ie ld 180, Stat ion 24, Field 24 Lihue Mana Pump, Field 420 Puu Opae Field 301 Fie ld U Puu Opae, Field 301 Field G-1; (replaced 1041.1) Wailua Reservoir H41 Kauai Variety Station, HSPA Lihue Variety Stat ion 1' Lihue Variety Stat ion 5 ' , Field H32A M30, Wailuakai 2 Waiakoal i Kaneha (replaced 1092.1) , Kaneda Monument, M4B Field W e e 2B, O l d Camp, M2B M30 M8, Field Makee 8, Halaula frl14AI Field Makee 14A, Anahola-Lihue Office, Residence Fie ld 170r Puukaele Reservoir Field 290 Field 300, Lepeuli, F ie ld 31 Puu Auau, Field 5 (Hawaiian Cannery), Moloaa, Moloaa Ocean Moloaa Mountain

APPEBDIX TABLE A.3. ACFWBGIiICAL LIST OF CUF3?EWJ! STAtrION NAMES

State NWS Quad. Key M. No. Ref.*

Ahualca 215 -30 H-44 Airport 216.30 H-44 IkMuulu Camp 4 89.50 H-62

Benchmark-Maunaloa 5ll.50 tMo-1 Benchmark-Wpio 816.30 $0.9 Burma Road 856 . lo 0-4

East Liwai 934.00 0456 K-8 EXW5 1061 .OO K-10 Eleele 927.00 0470 K-5 Ewa M i l l 741.00 0507 06 Field 003 Field 015 Field 070 Field 14 Field 18 Field 22 Field 23 Field 24 Field 25 Field 26 Field 29 Field 30 Field 30 Field 31-C Field 32-A Field 34-35 Field 38-A Field 55 Field 72 Field 95 Field 102 Field 104 Field 105 Field 108 Field 109 Field 116 Field 130 Field 155 Field 201 Field 205 Field 211 Field 220 81 8.10 0-5 Field 245 815 .OO 0.5 Field 301 419.00 M-7 Field 306 415 .OO M-7 Field 328 28.20 H-44 Field 360 966 .OO K-5 Field 370 981 .OO K-5 Field 402 321.50 M-8 Field 404 316.30 M-7 Field 405 316 .OO M-8 Field 405 316 -20 M-8 MPE: Refer to App. Table A.2 for alternate

* stat ion names not l i s t ed here. See Rep. R42 ~~ 1973a, pp. 15-148) and App. Figs. A.1-A.5 for stat ion locations.

t~ station on R42 quadrangle map.

State NWS Quad. StatiOnName KeyNo. No. =f.*

Field 408 M I Field 412 Field 413 Field 502 Field 525 Field 540 Field 541 Field 601 Field 603 Field 604 Field 604B Field 610 Field 612 Field 615 Field 700 Field 719 Field 806-2 Field 809 Field 811 V i l 3 Field 815 Field 821 Field 906 Field 906 V i l 7 Field 906-2 Field 9 l l Field 960 Moloaa Field A-4 Field F-2 Field H-32A Field H-46 Field I.,-1 Field G 3 A Field L-4 Field 6 2 4 Field LA-5 Field M-2B Field M-8 Field M-14A Field M-19 Field Makee 3C Field Mf+7 Field MC-9

H23 Canq? 9 Halenanahu Hamakua Makai Hamakua Mill Hamakuapko Hawaii Sub Off ice Hawi Helamo 9 Helemano 13 Kilo Airport Hormokaa Pasture traolehua Hukipo

--@ Kaheka Kdluahonu

APPIBDIX TABLE A. 3 . - a n t inued

State NWS Quad. Station Name State NWS Quad. Name Kev No. No. Ref. * KevNo. No. Ref.* a -. - - * - -

Kaneha Re~t3r~i.r 1092.00 3104 K-9 Oweula 17 861 .oo 0-4 Kawaihapai Kawaihapai Kawailoa 4 Kawailoa 20 Makai Kawela K e a l ia Keeaumoku Kekaha Kemoo 3 Kilauea Kilauea Field 17 Koa Ridge Kohala Kohala Maulili Kolo Koloa Koloa Mauka Kualwu Reservoir Kukuihele Landing Kukuiula Kunia Kunia Substation Lahaina Lalamilo Field Off Lihue Airport Lihue Variety Sta Limdloa Luwer Luakaha L P H I 4 LP Reservoir 5 30 Lua Mauka

Mahaulepu Makaweli Makin0 Mana Maunawi l i Maunawili Ranch McBKyde var sta Mealani Farm Mililani WW mamlua Moloaa Puuauau Naalehu New Stable N i u l i i Niu Ridge North Fork Nruanu Reservoir 4

0-1 0-1 0-4 0-4 H-3 5 K-LO 0-13 K-2 0-4 K-9 K-9 0-9 H-13 H-U K-1 K-8 K-8

- Paanau (McBryde) Paauhau Pahala PMA PMA Plant PRI Wahiawa Puakea Puehu Ridge -4 m 10 Puuauau Puuhi Puukol ii mu Lua Puunem? Puu Pulehu Res

IE-10 Ranch Reservoir 6 Reservoir 6 C6 Reservoir 9 C6 Reservoir 81 Robinson Gmq 1 Rock Pi le OS

Spalding lvIonument Station 3 Station 3 Station 5 Station 1 2 Station 14 Station 16 Station 4101

UH Mauka Camps Univ of E I a w a i i US Magnetic Obs

Village 6 Village 10 Village 13

Wahiawa Waiakoali CarrrP - Waialua Waianae Waiawa Waikoloa 'bJaimanal0 ESrp Sta Waimea 3 Waipio M p i o Field L waiubata west Lawai

m n d i x Figure A.1. Location map of pan evaporation stations, L;ana1i

20' 55'

20; 4 5

MOLOKA'I

See station i r l DOWALD Rep. R 4 2 0 New pan station

157'00' 156'45'

157'15'

I I I UHM-WRRC 157O15'

I

157OOO' 156O45'

r I 157'00' 156'45' I I

- -

- -

See station in DOWALD Rep. R42 0 New pan station

I UHM-WRRC

I

157'15' I

Appendix Figure A.2. Location map of pan evaporation stations, bloka'i

20' 55'

20' 45'

MAUl

I 0 New pan station I UHM-WRRC

1 I I

156'45' 156O30' 156O15' 156OOO'

Appendix Figure A.5. Location map of pan evaporation stations, Maui

160 30

HA WAI'I

H-34

Appendix Figure A.6. Location map of pan evapration stations, EGmai' i Island

18: 40

See station in DOWALD Rep. R 4 2 0 New pan station

UHM-WRRC - I I 1 I

18'

156OOO' -

40' 1 55O40' 155O20' 155OOO'

C C ~ 9 ao anor-c~ m~sentq*~r-w,mo min m a m ~ ~ p . ~ ~ ~ v - s t v

? * * * * * * * * a * * * a a a * ~ * * * ~ * I * ~ OS 0 a m N 3 PPNmNOU?OG G\C, r- tar- r-\om+ ~ \ C ; \ O L D ' Q Q \ O Q \ ~

- - * Y o ~ ~ - c - . L ~ * ~ r - PN ~ ~ ~ ~ s m ~ ~ n m a m 0 0 O L * N ~ 3 r * l W F r-lC0Mdr-m CDG2 COP L~I~-)F--~'Q?U'-PO

b * ~ * * * * * * * ? * * * * t * * @ * @ @ * * * * * * * a * * * * * * @ * e * w s * * R *

~ N ~ U ~ U ) O O ( ~ O P C D ~ X Q P - - O m n m p C O P Q ~ ~ S ~ S ~ ~ ~ N M e\i3~U'U'.a\~WOd4 aFtn@*K' PC- Corn f+-+bPPmW~aXnO

?- F P

c O U ' ? O ~ Q W d f i ~ N U3 3 + a ~ m f ' ? a M ~ @ mBmU3mVlfimONm P m ~ a ? ~ r ~ m s ? w r u m m awm3a6rnk l l rc m+m m=PNcmr-mmorm 0 CQ

~ a e e e ~ ~ ~ ~ ~ ~ * ~ ~ ~ ~ ~ e ~ m a ~ ~ ~ e ~ ~ e ~ ~ a s ? t * a ~ m * * * ~ * ~ * * ~~mrnm6r-mrnmm F, m ~ ~ o m m m m r - - ~ - h mmm ammrnr-r-hFmoa? a

C P1 F t-

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S * * . i t C @ l O 8 S ~ . * * * . 8 ~ S $ W a S O O ~ * S S W * * S * * * * S * S @ 8 * @

N C 2 3 0 0 ~ 0 0 ~ 0 O C n ~ cnopCOrpmf-@P a m ~ ~ P W ~ ~ P - ~ ~ ~ Q ~ P-WI p- rl- .err F c P" .-.

a m r-m ~ r ~ r n o n m ~ w m s ~ ~ r n ~ ~ m ~ ~ r n ~ w ~ r r - - r n ~ ~ c o m a ~ o m-W N XJW 0 f l rnNChNP-~-QOQw~bNt ' -@ N ~ ~ = . ? # C ~ I ~ ~ N C D ~ C ~ U ~ *

~ ~ * ~ ~ ~ e a a e e ~ * ~ ~ e * t o w ~ e a e n e a * * e * e a # * e ~ ~ * e e a * ~ * e 3m.3 a, mm at3t-.~r-fOmr-md;)r-oP*Q:(rmcnr-rco I - . ~ ~ ~ ~ F Q ~ ~ ~ ~ ~ J ~ o P - w w G Q u )

l- r

'4 rn a ,z? mmmmasm=rm nin r m CF smm qnrn3mams=r

m L.Q mmm 3raa m o a m ~ m m n o rnm r w m wrn~rsr-v-rnm * e -wmm mwv-rrm mm *wry rum NCU- Lnmwmma3ama a ~ e a ~ e e n ~ ~ n e a ~ * e ~ ~ ~ ~ a a 1 e e 1 a ~ 1 8 e ~ 0 1 1 e ~ 1 1 ~ 1 a ~ o ~ ~ * a a mmw mmam 3 5 3 r n 3 m 3 mmm a m JSN r n w r n ~ m m a 3 ~

m z t ~ m ~ s z r t n c ~ -r- m o e+e mem s m -or abmm%rv*o ~ N ~ L B O = r ~ ~ ~ ~ w m b - cam m e MPO w a r mcn ~ m n - m - o m w~t-wcn

@ * * ~ ~ ~ ~ @ * # ~ @ ~ ~ ~ * D @ # @ * I L ~ I I @ O D # U ~ ~ @ ~ I R ~ D * ~ * $ * * ~ 3 m 5 m m a + ~ w -3 win mma a w m m m p a w ~ r r n ~ r m 3 m o t . c mmz~m*

APPENDIX TA3LE B.1--Continued

JAN FEB APR W JUNE JULY ALK; SEPT OCT NCX7 DEC ANNUATL = - - - - - - - - - - KEY NO- (in.)------------------------ (in.)

mmm m ~ ~ ~ ~ ~ ~ ~ ~ o n a o m ~ m ~ m ~ m m ~ 1 o a \ ~ 1 m r l " m m ~ , m r n a ~ - 1 - ~ r h V? b W ~ ~ ~ ~ N ~ ~ ~ ~ ~ ~ ~ F ~ ~ ~ ~ ~ N F ~ ~ Q I Q ~ C V ~ F ~ ~ ~ ~ D N C O C C F ! ~ S

~ ~ 1 ~ ~ ~ ~ e ~ * 1 m 1 ~ ~ ~ m ~ ~ ~ e 1 ~ ~ m e e w ~ ~ ~ 1 ~ * t ~ 9 o e e a # ~ ~ 0 e P m~mPmmm~~m~mQ~P-PmmpF.F1.mCOwmaPCncD~OImF.cOmQ) m

r

pc NiB c) C O P

I * . . . .

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APPEXDIX TABLE B.l--(lontinued - JAN FEE3 MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC ANNUAL

STm YEAR - - - - - - - - - - - - - - - - - - - KEX NO- ( in. 1 --------------------------- (in.

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