Abstract

Evaporation and evapotranspiration are the major parameters in the hydrologic cycle and water resources research. Most precipitation is lost in the form of evaporation and evapotranspiration with the percentage varying from region to region globally. Therefore, accurate estimate of evapotranspiration is needed for numerous management activities and its application in rainfall-runoff models. The reference evapotranspiration ET_o concept has been gaining significant acceptance by scientists throughout the world since its introduction and it can also be estimated from pan evaporation E_p. E_p provides a measurement of the combined effect of temperature, humidity, wind speed and solar radiation on reference crop evapotranspiration. Hence, it is extensively used to estimate ET_o. A significant relationship exists between mean daily air temperature and observed mean daily pan evaporation in monsoon season in middle South Saurashtra region of Gujarat State (India). The objective of this study is to develop a model for prediction of Ep using mean air temperature. The four quantitative standard statistical performance evaluation measures, (R²), (MAPE), (RMSE) and Nash-Sutcliffe efficiency coefficient (E) are employed to evaluate the model. These performance measure ratings are found well within the acceptable limits. Prediction of E_p with the help of mean air temperature will lead to minimization of the time, cost, and equipment maintenance necessary for onsite monitoring and will help researchers to use data from other sources too.

Key words: Mean air temperature, pan evaporation, reference evapotranspiration, Saurashtra region.