Resent Estimation of Hydrologic Cycle Components in Gaza Strip Catchment

1

Recent Estimates of Hydrologic Cycle Components in Gaza

Strip Catchment

TAMER M. ALSLAIBI1 and YUNES K. MOGHEIR

2

1: Water Resources Engineering Dept., Islamic University of Gaza, Palestine,

[email protected]

2: Environmental Engineering Dept., Islamic University of Gaza, Palestine,

[email protected]

ABSTRACT

Accurate estimation of the hydrological cycle components is essential for an efficient

water resources management and planning. This is primary where there is a scarcity of

water resources like the case of Gaza Strip. This paper shows recent estimations of the

hydrologic cycle components: average annual precipitation, interception,

evapotranspiration, infiltration and the resulted runoff in the Gaza Strip catchment.

Various methods were selected from the literature such as Thiessen method and Penman

Equation and other estimation methods. The data were collected from the water

institutions in the Gaza Strip to perform the analyses. The analyses are considered as

recent since the data collected form years 1999 to 2006.

The results revealed that the average annual precipitation of rainfall in Gaza Strip is 350

mm/year and the interception percentage by agricultural, urban, road and industrial uses

are 5.8%, 4.3%, 2.3% and 1.8% respectively. The average annual evapotranspiration in

Gaza Strip is 128.2mm/year, which represents 36.6%. In addition, the net rainfall

infiltrates through the soil is 77.8mm/year, which represents 22.2%. Therefore, for the

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steady state conditions, the water budget of the Gaza Strip indicates that the percentage

of rainfall water which is generated as a runoff is 27.0%.

The findings of this paper can be used to update the water budget of the Gaza catchment

area. Meanwhile, this could update the water resources management and planning studies

which are used regularly by many institutions and researches.

Keywords: Gaza catchment, hydrological cycle, water budget, management and

planning.

1. INTRODUCTION

The Hydrological Cycle is a never ending process. One of the most accessible portions of

water in this cycle is precipitation (Abdul Mukti et al., 2005) . The hydrological cycle

components can be classified as: precipitation, infiltration, evaporation, transpiration,

surface runoff and groundwater flow. The cyclic movement of the water from the sea to

the atmosphere and then by the precipitation to the earth, where it collects in streams and

runs back to the sea, is referred to as the hydrological cycle. Such cyclic order of events

dose occur but it is not so simple as that (Figure 1). The cycle may short-circuit at several

stage, for example, the precipitation may fall directly into the sea, lakes or river courses.

In addition, there is no uniformity in the time a cycle takes. During droughts it may

appear to have stopped altogether, during floods it may seem to be continuous. The

intensity and frequency of the cycle depend on geography and climate, since it operates

as a result of solar radiation, which varies according to latitude and season of the year.

The various parts of the cycle can be quite complicated and man can exercise some

control only on the last part, when the rain has fallen on the land and is making its way

back to the sea.

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Water in the sea evaporates under solar radiation and clouds of water vapor move over

land areas. Precipitation occurs as snow, hail, rain and condensate in the form of dew,

over land and sea. Snow and ice on land are water in temporary storage. Rain falling over

land surfaces may be intercepted by vegetation and evaporate back to the atmosphere.

Some of it infiltrates into the soil and moves down or percolates into the saturated ground

zone beneath the water- table, or phreatic surface. The water in this zone flows slowly

through aquifers to river channels or sometime directly to the sea. The water that

infiltrates also feeds the surface plant life and some gets drawn up into this vegetation

where transpiration takes place from leafy plant surfaces (Wilson, 1998).

The water remaining on the surface partially evaporates back to vapour, but the bulk of it

coalesces into streamlets and runs as surface runoff to the river channels. The river and

lake surfaces also evaporate, so still more is removed here. Finally, the remaining water

that has not infiltrated or evaporated arrives back at the sea via the river channels. The

groundwater, moving much more slowly, either emerges into the stream channels or

arrives at the coastline and seeps into the sea, and the whole cycle starts again (Wilson,

1998).

The change of the land uses has a direct impact of the quantities of the hydrological

components. For example, land uses in Gaza Strip vary between agricultural, industrial,

urban and roads. In this article the recent changes of the quantity of the hydrologic cycle

according to the recent changes of the land uses was estimated for year 2006.

2. STADY AREA

Gaza Strip is a coastal area that is located at the southwestern of Palestine and eastern

part of the Mediterranean Sea. It is bordered by Egypt from the south and Negev desert

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from the east. Its length from south to north is about 45 km, and from west to east varies

between 6 and 12 km. The Gaza Strip area is classified as a semiarid region. The highest

mean annual temperature is 30.85 C°, while the lowest mean annual temperature is 14.16

C°. The average annual wind speed in Gaza Strip is about 10.92 Km / hr (PMO, 2006).

3. ESTIMATION APPROACHES

3.1 Data Collection

The approach followed in this article is a disk study approach which mainly depends on

collecting the updated and recent data. The data can be grouped in two categories:

1. The data related to the land use up to year 2006 which mainly collected from

Ministry of Agriculture and Ministry of Planning (MOA, 2006) (MOP, 2005).

2. The data related to the hydrological cycle components up to year 2006 such as

rainfall, daily temperature, relative humidity, wind velocity and hour of sunshine.

These data were collected from Palestinian Meteorological Office (PMO, 2006)

(PWA, 2006).

Figure (1): Typical Hydrological Cycle

(http://visual.merriam-webster.com)

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3.2 Data screening and analyses

The collected data were screened to check the errors that might be encountered in the

several steps of measurements and data transmittion. Some of the collected data is used

in a direct way for the estimation procedures such as the estimation of rainfall. Other data

are used indirectly to compute some of the hydrological components such as evaporation.

3.3 Hydrological Components Estimations

The hydrological components were estimated and computed by using empirical methods,

equations from the literature. Some computer programs such as Excel spread sheets,

AutoCAD, Geographical Information System (GIS) are used for carrying out the

computations and to visualize the results of the analyses.

3.3.1 Precipitation

The average amount of regional precipitation in Gaza Strip is computed using Thiessen

Method as follows (Viessman and Lewis, 2002):

A

APp

avg

* (1)

Where,

Pavg : is the average amount of perception in mm/year

A : is the area of the polygon determined by Thiessen method in Km2.

In Thiessen method the rainfall recorded at each station is given a weightage on the

basis of an area closest to the station (Viessman and Lewis, 2002). The method mainly

consists of to divide the catchment area into Thiessen polygons depend on the locations

of the rainfall station as shown in Figure 2.

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Figure (2): Estimation of average precipitation over Gaza Strip by Thiessen

Method and the soil classifications.

3.3.2 Evapotranspiration

Evapotranspiration in Gaza strip is calculated for year 2006 using The Penman method

(Viessman and Lewis, 2002), as follows:

27.0

27.0

EHET (2)

)0098.01)((35.02uee a

E

(3)

)9.01.0)(092.056.0()55.018.0)(1(5.0

SBSrRH ed (4)

Where,

∆ : the slope of the saturated vapour curve of air at absolute temperature (mm

Hg/oF)

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H : the daily heat budget at the surface (estimate of net radiation mm/day)

E : daily evaporation (mm)

ET : the evaportranspirtaion (mm/day)

R : the mean monthly radiation

r : reflection coefficient (ranges between 0.05 to 0.12)

B : a temperature – dependent coefficient

S : the estimated ratio of actual duration of bright sunshine to maximum possible

duration of bright sunshine

ed : the actual vapour pressure of the air at a standard height (usually 2 m)

ea : the saturation vapour pressure

U2 : wind velocity in m/s at 2m height

3.3.3 Interception

The interception of rainfall by different land uses in Gaza Strip is computed as follows

(Viessman and Lewis, 2002):

KETSLi (5)

Where,

Li : the volume of water intercepted (mm, in)

S : the interception storage whose values varies from 0.25 to 1.5 depending on the

nature of vegetation

K : ration of vegetal surface area to its projected area

E : evaporation rate in (mm/h) during the precipitation

T : duration of rainfall in hours

3.3.4 Infiltration

The infiltration of rainfall by different type of soil in Gaza Strip is computed as follows:

Q = P A C (6)

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Where

P :Net rainfall for each station in (mm)

A :Area of each type of soil for each station (Km2)

C :Recharge coefficient.

3.3.5 Runoff

The quantity of rainfall run over the surface in Gaza Strip is computed by considering

the water budget of the Gaza Strip catchment area which is describes as follows:

R = P-ET-Li-I (7)

Where

R : runoff in mm/y

P : precipitation in mm/y (Eq. 1)

ET : evapotranspiration in mm/y (Eq. 2)

Li : interception in mm/y (Eq. 5)

I : infiltration in mm/y (Eq. 6)

4. RESULTS AND DISCUSSIONS

The average perception in Gaza Strip of years 2000 up to 2006 is computed using Eq. 1

and the results was tabulated in Table 1. The average precipitation in Gaza Strip is

350.24 mm/year. In frequent studies conducted in the Gaza Strip for the past 10 years,

380 mm/year was considered as an average precipitation. This number was computed as

an arithmetic mean of the yearly rainfall in each station. However, the result of the

current article which sows the average perception is 350 is more accurate since it is the

first time that a well known method such as Thiessen is used for such analyses.

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The evapotranspiration (ET) in Gaza Strip is computed using Eqs. 2, 3 and 4. The

results of the computations are presented in Table 2. It was found that the average ET

for the non rainy days was 1646 mm/y and that one for the rainy days was 128

mm/year. In average the total ET amount is around 36.6 % of the total rainfall. It is

believed that this quantity is more precise than that was used in most of ET estimation

studies. In current study the total ET in Gaza Strip was computed, while other studies

computed ET for one station and mostly the Gaza Station was used as a typical for all

Gaza Strip. For instance, Palestinian Meteorological Office computed the ET for rainy

months as 641 mm/y while the current study revealed that ET is 577 mm/y.

The interception of rainfall by different land uses in Gaza Strip is computed and

simplified using Eq.5. The results of the computation are shown in Table 3. It can be

concluded that the average interception quantity for year 2006 is 20.38 mm/y which

form 5.82 % of the total rainfall.

The infiltration of rainfall by different type of soil in Gaza Strip is computed using Eq. 6

and the results of the calculation are presented in Table 4. Notice that classification of

different soil types is used in the computations. Figure 2 shows the description of the

soil type in Gaza Strip. Another parameter which may influence the infiltrated amount

is the runoff coefficient which mainly depends on the land use. This coefficient varies

between 0.025 to 0.7. As a result the average infiltration rate for year 2006 is 77.83

mm/y which form 22.23 % of the total rainfall in the Gaza Strip.

As shown in Eq. 7, the water budget method is used to compute the remaining runoff

quantity. It was found that the quantity of rainfall run over the surface in Gaza Strip for

year 2006 was 94.6 mm/y that form 27 % of the total rainfall.

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5. CONCLUSION

The effect of land uses changes, in the Gaza Strip, on the hydrological cycle

components was studied for year 2006. Thiessen method was used to estimate the

amount of rainfall that precipitate in Gaza Strip and it revealed that it equals 350

mm/year. Penman method indicated that 128 mm of the rainfall is lost as

evapotranspiration every year. This quantity is transferred to the atmosphere as water

vapor in a rainy days of a year which represents 36.62% of the rainfall quantity. The

study indicated that the percentage of the intercepted rainfall by different uses of land

such as agricultural, urban, roads and industrial are 5.82%, 4.25%, 2.32%, and 1.78%

respectively. About 77.83 mm/year of the rainfall quantity infiltrates to the ground,

which represent 22.23%. At the end, approximately 94.6 mm/year run over the land

which represents 27.03% from the total rainfall.

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Table (1): Estimation of the average precipitation over Gaza Strip area by Thiessen method for year 2006.

Date Year RAINGAGE STATIONS

B Hanon B Lahia Jabalia Shati Remal Tuffah Moghragah Nussirate Dr-Elbalah Khan Younis

Khuzaa Rafah

Sum 99/00 (mm/y) 406.4 390.5 388.5 425.1 334.8 357.2 368.3 278.5 256.7 191.8 142.2 198.5

Sum 00/01 (mm/y) 497.5 490.4 540 478.9 511.9 533.4 563.6 558.3 550.5 381 284.3 308

Sum 01/02 (mm/y) 548.4 542 565.5 522.1 544.4 604.3 660.5 545.5 390.6 311.7 258.5 241.7

Sum 02/03 (mm/y) 801.5 724 692.6 627 599 653.5 790.7 446.2 372.6 298 261.2 220.8

Sum 03/04 (mm/y) 349.4 393.1 366.4 324.5 378.2 429.6 466.1 316.5 316.4 207 186 173.5

Sum 04/05 (mm/y) 358.7 320.6 345.5 296.6 310.7 350.7 323.6 405.0 345.5 373.0 368.0 360.2

Average Precipitation (P)

(mm/y)

448.73 433.38 439.12 405.14 405.87 443.70 480.67 386.33 338.19 293.75 250.03 227.66

Area of each station (km2) * 27.36 15.35 14.11 2.98 12.50 25.50 34.40 28.93 38.40 86.70 43.40 35.00

P Area 12277.2 6652.4 6196.0 1207.3 5073.4 11314.3 16535.1 11176.4 12986.6 25468.1 10851.3 7968.1

Annual precipitation

(mm/year) 350.24

* The Thiessen method is used to determine the area as shown in Figure 2

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Table (2) Estimation of evapotranspiration quantity in Gaza Strip by Penman Method for year 2006

Penman Method

Parameters

Months

JAN FEB MAR APR MAY JUN JUL AUG SEB OCT NOV DEC

15.6 13.9 15.0 19.3 23.2 25.1 26.9 27.5 25.9 23.7 20.2 15.7

∆ 0.50 0.50 0.50 0.60 0.65 0.80 0.83 0.85 0.80 0.75 0.63 0.52

R.H. 0.64 0.64 0.68 0.64 0.72 0.76 0.73 0.73 0.65 0.70 0.65 0.62

e0 (mm Hg) 12.78 12.00 12.78 17.53 21.00 23.76 28.00 29.00 27.00 23.00 17.53 12.78

ea (mm Hg) 8.18 7.68 8.69 11.22 15.12 18.06 20.44 21.17 17.55 16.10 11.39 7.92

u (m/day) 168 235 205 168 140 144 153 154 163 158 147 157

R (mm H2O/day) 8.50 10.50 12.70 14.80 16.00 16.50 16.20 15.30 13.50 11.30 9.10 7.90

B 14.00 13.70 14.00 14.80 15.50 15.80 16.34 16.34 16.00 15.90 15.00 14.00

r 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09

n (hr) 4.5 4.6 6.4 7.9 10.2 10.8 11.1 10.3 9.4 8.6 5.9 4.4

N (hr) 10.1 10.9 11.8 12.8 13.6 14.1 13.9 13.2 12.2 11.2 10.3 9.9

S 0.45 0.42 0.54 0.62 0.75 0.77 0.80 0.78 0.77 0.77 0.57 0.44

E (mm) 4.26 4.99 4.31 5.85 4.88 4.81 6.61 6.88 8.59 6.15 5.24 4.31

H (mm/day) 1.21 1.93 3.15 4.55 6.20 6.92 7.20 6.69 5.20 3.79 1.80 0.94

ET (mm/day) 2.28 3.01 3.56 4.95 5.81 6.39 7.06 6.73 6.06 4.42 2.83 2.10

ET (mm/month) 70.6 93.2 110.2 153.6 180.1 198.0 218.8 208.8 187.7 137.0 87.7 65.0

Number of rain days 9.00 11.00 9.00 5.00 0 0 0 0 0 0 1.00 7.00

ET (for rain days) 20.49 33.07 32.00 24.77 0 0 0 0 0 0 2.83 14.67

AVG. ET (mm/year) for all months = 1711

AVG. ET (mm/year) for rainfall months = 580.3

AVG. ET (mm/year) for rain days = 127.83

Percentage of ET for rain days from total rainfall = 36.53%

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Table (3): Estimation of interception of rainfall in Gaza Strip

Eq (5) Parameters MONTHS

JAN. FEB. MAR. APR. MAY JUN. JUL. AUG. SEB. OCT. NOV. DEC.

S (in) 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03

K 0.494 0.494 0.494 0.494 0.494 0.494 0.494 0.494 0.494 0.494 0.494 0.494

AVG. E (mm/day) 2.26 2.83 3.66 4.83 5.33 6.12 6.56 6.57 5.39 4.47 3.04 2.00

AVG. E (in/hr) 0.0037 0.0046 0.0060 0.0079 0.0087 0.0100 0.0108 0.0108 0.0088 0.0073 0.0050 0.0033

Rain days /month 11.00 9.00 5.00 2.00 0 0 0 0 0 3.00 4.00 9.00

Time period (hr/day) 6.00 6.00 6.00 6.00 0 0 0 0 0 6.00 6.00 6.00

t (hr) 66.00 54.00 30.00 12.00 0 0 0 0 0 18.00 24.00 54.00

Li (in/month) 0.151 0.154 0.119 0.077 0 0 0 0 0 0.095 0.089 0.118

Li (mm/month) 3.83 3.91 3.02 1.96 0 0 0 0 0 2.42 2.26 2.99

AVG. Li (mm/year) = 20.38

Percentage of Li from Rainfall= 5.82%

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Table (4): Estimation of infiltration quantity in Gaza Strip for year 2006.

Stations Soil types Area (km2) Rainfall

(mm/year)

Evaporation Net rain

(m/year)

Recharge

coefficient

Infiltration

(10 6 m

3)

1 Dark brown / reddish brown 18.5 448.73 128.0 0.321 0.025 0.15

Sandy regosols 10.58 448.73 128.0 0.321 0.7 2.38

2 Sandy regosols 15.55 433.38 128.0 0.305 0.70 3.32


Sandy regosols 14.79 439.12 128.0 0.311 0.7 3.22

4 Sandy regosols 3 405.14 128.0 0.277 0.7 0.58


Loess soils 1.95 405.87 128.0 0.278 0.15 0.08

Sandy regosols 10.1 405.87 128.0 0.278 0.7 1.96


Loess soils 11.63 443.70 128.0 0.316 0.15 0.55

Sandy regosols 1.23 443.70 128.0 0.316 0.7 0.27


Loess soils 8.09 480.67 128.0 0.353 0.15 0.43

Sandy loess soil 3.61 480.67 128.0 0.353 0.3 0.38

8 Dark brown / reddish 0.00205 386.33 128.0 0.258 0.025 0.00

Loess soils 2.23 386.33 128.0 0.258 0.15 0.09

Loessal sandy soil 6.98 386.33 128.0 0.258 0.25 0.45

Sandy loess soil 15.43 386.33 128.0 0.258 0.3 1.20

Sandy regosols 3.78 386.33 128.0 0.258 0.7 0.68



Sandy loess soil 6.99 338.19 128.0 0.210 0.3 0.44

Sandy regosols 12.37 338.19 128.0 0.210 0.7 1.82



Sandy loess soil 4.59 293.75 128.0 0.166 0.3 0.23

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Sandy loess soil over loess 21.47 293.75 128.0 0.166 0.35 1.25

Sandy regosols 27.35 293.75 128.0 0.166 0.7 3.17

11 Loessal sandy soil 13.35 250.03 128.0 0.122 0.25 0.41

Sandy loess soil 3.47 250.03 128.0 0.122 0.3 0.13


12 Loessal sandy soil 17.95 227.66 128.0 0.100 0.25 0.45


Sandy regosols 9.77 227.66 128.0 0.100 0.7 0.68

Sum 28.35

Total amount of water infiltrate to the ground (mm/year) = 77.8

Percentage of infiltration from Rainfall = 22.2%

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6. REFERENCES

Abdul Mukti M., Noor F. and Pheng T., 2005, Rainwater Harvesting – An

Opportunity Neglected, Universitiy Teknologi Malaysia, Water Malaysia Issue

No:10.

Hydrologic cycle. [Accessed in April. 2010]. Available online:

http://visual.merriam-webster.com/earth/environment/hydrologic-cycle.php.

Ministry of Agricultural (MOA), 2006, Software data, Gaza Strip, Palestine.

Ministry of Planning (MOP), 2005, Regional plan of the southern governorates

2005-2020, Gaza Strip, Palestine.

Palestinian Meteorological Office (PMO), 2006, Software data, Gaza Strip,

Palestine.

Palestinian Water Authority (PWA), 2006, Software data, Gaza Strip, Palestine.

Viessman W. and Lewis G., 2002, Introduction to Hydrology, 5th

edition, New

York: HarperCollins College.

Wilson E., 1998, Engineering Hydrology, 4th edition, University of Salford.

http://visual.merriam-webster.com/earth/environment/hydrologic-cycle.php

Resent Estimation of Hydrologic Cycle Components in Gaza Strip Catchment

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