Evapor-trans2-komplit

8/7/2019 Evapor-trans2-komplit

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E V A P O R A S I

Oleh : Emilya Nurjani


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Hampir 80% berasal dari laut,sisanya 20% berasal daridaratan dan vegetasi.

Most evaporated water exists asa gas outside of clouds and

evaporation is more intense inthe presence of warmertemperatures.

Evaporasi dan Evapotranspirasi


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FAKTOR YANG

BERPENGARUH


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PARAMETERCUACA

FAKTORTANAMAN

KONDISI LINGKUNGANDAN

PENGELOAAN


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PARAMETER CUACA


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RADIASI MATAHARI

Sumber utama energi bumienergi (terpancar 56 x 1026

kalori, sampai di bumi hanya5 x 10-10)

Radiasi gelombang pendek

(< 3 m) : matahari, radiasigelombang panjang

( > 3 m) : bumi


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insolasi


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Annual variation in extraterrestrial radiation (Ra)

at the equator, 20 and 40 north and south


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Annual variation of the daylight hours (N)

at the equator, 20 and 40 north and south


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SUHU

Temperature is a measure of the

level of sensible heat of matter(solid, liquid, gas)


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ALAT UKUR SUHU


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BEBERAPA PERSAMAANThe relative humidity (RH) expresses the degree of saturation of theair as a ratio of the actual (ea) to the saturation (e(T)) vapourpressure at the same temperature (T):

As saturation vapour pressure is related to air temperature, it canbe calculated from the air temperature. The relationship isexpressed by:

wheree(T) saturation vapour pressure at the air temperature T [kPa],T air temperature [C],exp[..] 2.7183 (base of natural logarithm) raised to the power [..].


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Saturation vapour pressure shown as afunction of temperature: e(T) curve


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Variation of the relative humidity over 24 hours for

a constant actual vapour pressure of 2.4 kPa


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ANGIN


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Airrisesoverwarm areasandsinks

overcold areas

Airrises inwarm

regions where

pressureislow

(convection)

eg the tropics

Airdescends incold

areas where

pressureishigh

(subsidence)

eg the poles


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effect of wind speed on evapotranspiration in

hot-dry and humid-warm weather conditions


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PerhitunganE

vapotranspirasi


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Gambaran Perhitungan Evapotranspirasi


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BerdasarkannilaiEToFAO Penman-Monteith

equation

The FAOPenman-Monteith method isrecommended as the method fordetermining reference ETo. The FAOPenman-Monteith method requiresradiation, air temperature, airhumidity and wind speed data.

The Penman-Monteith form of thecombination equation is:

where Rn is the net radiation, G is thesoil heat flux, (es - ea) represents thevapour pressure deficit of the air, r ais the mean air density at constantpressure, cp is the specific heat of theair, D represents the slope of thesaturation vapour pressuretemperature relationship, g is thepsychrometric constant, and rs and raare the (bulk) surface andaerodynamic resistances.


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Berdasarkan data meteorologi

ETo = 0.0023(Tmean + 17.8)(Tmax - Tmin)0.5 Ra


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DeterminasinilaiET0

ETo = referenceevapotranspiration [mmday-1],Rn = net radiationat the crop surface [MJ m-2 day-1],G = soil heat fluxdensity [MJ m-2 day-1],T = air temperatureat 2 m height [C],

u2 = windspeedat 2 m height [ms-1],es = saturationvapourpressure [kPa],ea = actualvapourpressure [kPa],es- ea = saturationvapourpressuredeficit [kPa],D = slopevapourpressure curve [kPa C-1],g = psychrometric constant [kPa C-1].


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ETobeberapa tipeiklim (mm/hari)

Region Suhu rata-rata harian (oC)

Dingin(~10)

Sedang(20)

Panas(>30)

Tropik dan SubtropikHumid dan sub-humid

2-3 3-5 5-7

Arid dan semi-arid 2-4 4-6 6-8

Temperate

Humid dan sub-humid

1-2 2-4 4-7

Arid dan semi-arid 1-3 4-7 6-9


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Evapor-trans2-komplit

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