Annals of Arid Zone 34(4) : 263-265, 1995

Estimation of Evaporation from Different Meteorological Parameters

Ram Singh, Om Prakash and M.L. KhicherDepartment of Agricultural Meteorology,CCS Haryana Agricultural University, Hisar 125 004, India

Abstract: Simple correlations between different meteorological parameters and evaporation,measured from US Class A open pan evaporimeter, were worked out. The highest correlationvalue (0.85) was obtained with maximum air temperature, followed by wind speed (0.82).The coefficient of determinates for minimum air temperature, relative humidity and brightsunshine hours were 0.70,-OS6 and 0.15, respectively. The highest coefficient of determination\yas 0.92, when all these meteorological parameters were considered together.

,Key words: Evaporation, meteorological correlation, evaporimeter, temperature, wind, coef-ficient, humidity sunshine.

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The measurement or estimation of evaporationis useful for scheduling of irrigation and watermanagement conservation in any region. The rateof evaporation depends on meteorological factorssuch as radiation, temperature of air, wind speedand relative humidity at or ...near the evaporationsurface.

There are several simple devices and empiricalmethods for estimating evaporation. Evaporationmeasurements using evaporimeter tanks or panare further controlled by the size, depth, shape,material and colour of the tank or pan and natureof exposure. Small containers of different kindcan measure evaporation more accurately butthe measurements of evaporation from the surfaceoflarge water bodies, crop fields are also requiredand, therefore, several workers have used differentmethods for. estimating evaporation.

Linacre (1967) evaluated that the evaporationrate can be estimated only from radiation meas-urements ignoring humidity and wind. Tanner(1968) observed that radiation methods for es-timating evaporation are among the better em-pirical methods. Singh et al. (1992) made anattempt to find the relationship betweenmeteorological parameters and observed valuesof evaporation from an open pan evaporimeter.They used one year data, taking weekly averageof different meteorological parameters, fordeveloping regression equations. But, in the

present study, 14 years monthly average dataof different meteorological parameters have beenused for developing regression equations, to es-timate evaporation and ~he calculated values werecompared with observed values.

Material and Methods

The meteorological parameters, viz., maximumand minimum air temperatures eC), wind speed(km h-1), relative humidity (%), duration of brightsunshine (h) and rate"pf evaporation (mm),recorded daily at agro-meteorological obser-vatory, installed at Research Farm of ChaudharyCharan Singh Haryana Agricultural University,Hisar (Latitude 29°10'N and Longitude 75°46'E)during 1980 to 1993, were utilised. The dailyevaporation is measured with the help of USClass A open pan evaporimeter (Hook GaugeType). The meteorological data were analysedto calculate the monthly average values of different

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parameters, (i) maximum air temperature andevaporation, (ii) minimum air temperature andevaporation, (iii) relative humidity and evapora-tion, (iv) wind speed and evaporation, and (v)bright sunshine hours and evaporation. A multiplecorrelation was also computed amongst all thesemeteorological parameters together and evapora-tion. The monthly average evaporation rates, cal-culated from 'various developed regressionequations, were compared with observed evapora-tion rates.

264 SINGH et al.

The maximum value of coefficient of deter-mination (R2 = 0.92) was obtained when all

two parameters was 0.70. Raney (1959) noticedthat evaporation was influenced by wind speed,humidity, temperature and soil moisture.

Y = 2fJ.679 - 0.585 Tmax + 0.653 Tmin -0277 Rh + 0.215 Ss + 0.336 Ws

(R2 = 0.92)

After considering all these meteorologicalparameters together, a multiple regression equa-tion has been ~eveloped for the calculation ofevaporation for Hi~ar region. The equation is

evaporation rate (mm month-t)maximum air temperature (OC)minimum air temperature (0C)relative humdity (%)sunshine (h)wind speed (km hot)

where,YTmaxTminRhSsWs

Results and Discussion

Out of five meteorological parameters con-sidered, four had a significant influence on theevaporation rate (Table 1). The relationship be-tween bright sunshine hours and evaporation wasnon-significant. Singh et al. (1992) had alsoreported the non-significant correlation betweenthese two parameters. The highest correlationwas found between maximum air temperatureand evaporation rate (0.85), followed by thatof wind speed and evaporation rate (0.82). Theevaporation rate was negatively correlated withrelative humidity (0.56). Singh et al. (1992) andVamadevan (1971) had observed that relativehumidity had an inverse correlation with theevaporation rate. The rate of evaporation is alsohighly influenced by minimum air temperature,as the coefficient of determination between these

Relation between evaporation and meteorologicalparameters

11

10

9

E8.§.~ 7!;i0:: 6o0..~ 5w

4

3

2OBSERVED FROM OPE;NPANESTIMA TED

oFMAMJ J AS OND

MONTHS

Fig. 1. Obsen'ed e\'liporation from open pall el'aporimeter alld estimated evaporation usingmultiple regression based on different meteorological parameter (Average 1980-93).

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ESTIMATION OF EVAPORATION

. Table 1. Simple regression equations developed between evaporation and different meteorological parameters

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Meteorological parameters

Maximum air tl:mperatureWind speed (km h-1)

Minimum air temperatureRelative humidity (%)Sunshine (h)

Regression equations R"

("C) Y -7.74 f: 0.432 • X 0.85

Y -052 + 1.120 • X 0.82

("C) Y . 050 + 0.3~ • X 0.78

Y 15.09 - 0.156 • X 056

Y 2.87 + 0.357 • X 0.15

five meteorol.ogical parameters were consideredtogether to see the combined effect onevaporati.onrate.

Comparison between observed and estimatedevaporation

The estimated evaporation rates from multipleregressi.on equati.on developed fr.om differentmeteorological parameters, were compared withobserved evaporati.on rates from open panevaporimeter (Fig. 1). The estimated values werevery close to the .observed values of evap.oration.However, the estimated values obtained fr.omregressi.on equati.ons .of maximum temperatureand wind speed are also very close to .observedevaporation as c.ompared t.o other 'regressionequations. The estimated evap.orati.on .obtained

. from the simp:~ regression equations, using rela-tive humidity and sunshine hours, .overestimatedevap.orati.on during winter seas.on imd underes-timated during summer and rainy seasons. Similar

results have been rep.orted by Iruthayaraj andM.orachan (1978)..

ReferencesIruthayaraj, M.R and Morachan, Y.B. 1978. Relationship

between evaporation from different evaporimeters andmeteorological parameters. Agricultural Meteorology 19:93-100.

Linacre, E.T. 1%7. Oimate and evaporation from crops.Journal of Irrigation and Drainage Division, AmericanSociety of Civil Engineering Proceeding 93: 61-79.

Raney, W.A. 1959. Evaluation of evapotranspiration in fieldplots. TransactionsoftheAmerican Society of AgriculturalEngineers 1: 41. '

Singh, S., Rao, V.U.M. and Singh, D. 1992. Relationshipbetween evaporation from USWB Oass A open panevaporimeter and meteorological parameters. HatyanaAgricultural University,Journal of Research 11: 21-24.

Tanner, C.B. 1968. Evaporation of water from plants andsoils. In Water Deficits and Plant Growth (Ed. T.T.Kozolwski). Vol. 1, pp. 73-106. Academic Press NewYork ..

Vamadevan, V.K. 1971. Influence' of meteorological elementson evapotranspiration of rice. ldojaras KolonlenY0menlSeparatum S' & 6: 326-330.