Mathematical Models for Estimating Evapotranspiration of a Hill Evergreen Forest in Kog Ma Watershed, Doi Pui, Chiang Mai Province; 1. Model Formulation, Calibration and Verification

Abstract

An application of a mathematical model was studied coupling the Penman, Penman-Monteith and Rutter’s models to estimate the evapotranspiration of a hill evergreen forest at Huai Kog Ma, Doipui, Chiang Mai province, northern Thailand.  The results obtained from the coupled model were compared with those measured from the Eddy-Correlation method.  To calibrate and verify the results from the model, Nash and Sutcliffe’s equation (NSE) was employed to indicate model efficiency.

            The results on the efficiency of the model calibration for rainfall-intercepted water derived from the Rutter’s model based on 10 and 30 minute data results produced an average NSE equal to 0.8858 and 0.8890, respectively.  The average NSE of the transpiration estimation based on the Penman-Monteith model using 10 minute data was higher than from using 30 minute data with values of 0.3965 and 0.3181, respectively.  The model verification of the rainfall interception showed a lower efficiency compared with that from the calibration process.  The average NSE of the interception estimation using 10 minute data was lower than using from 30 minute data with values of 0.7662 and 0.8349, respectively.  Verification of the transpiration estimation showed that the average NSE using the 30 minute data was higher than from using 10 minute data with values of 0.3596 and 0.3433, respectively.

Keywords: evapotranspiration, mathematic model, Huai Kog Ma watershed, hill evergreen forest