Kwok, Chee Yan

Lee, Teang Shui

M., Hazrat

Universiti Putra Malaysia Institutional Repository

FOR Category F10700: Engineering SciencesMODELLING EVAPORATION ANDEVAPOTRANSPIRATION UNDER CLIMATECHANGE IN MALAYSIAM. Hazrat, T.S. Lee and C.Y. KwokFaculty of EngineeringUniversiti Putra Malaysia, 43400 UPM, Serdang, Selangor,MalaysiaKeywords: climate change, evaporation, evapotranspi-ration, simulation, perturbation.IntroductionClimate change has a direct effect on hydrology through itslink with evapotranspiration. This study assessed the poten-tial impact of climate change on the evapotranspiration.Materials and MethodsMeasured climatic data from the MUDA Irrigation Schemewere obtained from their computerised records. These wereused in the various models to compute evaporation andevapotranspiration (Penman, 1948). Methods to estimatefree-surface evaporation EP and potential evapotranspirationET, without any model calibration parameters, for monthlytime series are presented. (Fennessy and Kirshen, 1994)Model results are calculated without keeping any model cali-bration parameter by using observed average historic (1980-97) meteorological data (Monteith, 1965) and compared withUSBR Class-A black pan evaporation data (1971-97) fromthe Muda Agricultural Development Authority, Malaysia.The long-term monthly averaged daily estimates of Ep fordifferent months were compared with measured pan evapo-ration.Results and DiscussionResults of this simulation showed that the long term dailyestimates of Ep for different months simulate more than 95%with the observed pan evaporation data. The variations areslightly more from December to March. It is thought that thevariation is due to lower rainfall during these months. In thestudy on the effect of climatic influence all model equationscontaining temperature terms were set dependent of tem-perature. ETp time series is perturbed by varying monthlytemperature rises from 21°C to 41°C with 0.2°C increment toinvestigate the sensitivity of that series (Milly, 1992). Theseshowed that the temperature had significant effects on ETpfor each month with a value of R2= 0.9875.ConclusionsThe model developed was able to estimate 95% of the meas-ured pan evaporation. Results from the study showed thattemperature had significant effects on monthly ETp.ReferencesFennessy, N.M. and Kirshen, P.H. 1994. Evaporation and Evapo-transpiration under Climate Change in New England. Journal ofWater Resources Planning and Management. 120(1): 48-69.Milly, P.C.D. 1992 Potential Evaporation and Soil Moisture in Gen-eral Circulation Models. J Climate. 5(3): 209-226.Monteith, J.L. 1965. Evaporation and the Environment. Symp. Soc.Expt. BioI. 19: 205-234.Penman, H.L. 1948. Natural Evaporation from Open Water Bare Soiland Grass. Proc. R. Soc. London. 193: 120-145.Supported by lRPA Grant 01-02·04·013/265

Modelling evaporation and evapotranspiration under climate change in Malaysia

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Modelling evaporation and evapotranspiration under climate change in Malaysia

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