Estimation of Spatial and Temporal Reference Evapotranspiration in the Chao Phraya River Basin

Abstract

In the hydrological cycle and water use, evapotranspiration is one of the most important components because it represents a loss of usable water from the hydrologic supply. The purposes of this research are to calculate spatial and temporal reference evapotranspiration using FAO Penman-
Monteith and Kriging methods and to determine the relationship between mean monthly temperature and monthly reference evapotranspiration. To achieve the first purpose, daily reference evapotranspiration from 1971 to 2002 was computed for each weather station using the FAO Penman-Monteith method. The average of monthly reference evapotranspiration in each weather station was figured. Thereafter, monthly reference evapotranspiration, that is point reference evapotranspiration, was interpolated using the Kriging interpolation. The result of this calculation is spatial reference evapotranspiration or reference evapotranspiration map from January to December (temporal). After spatial and temporal reference evapotranspiration was calculated, the relationship between mean monthly temperature and mean monthly reference evapotranspiration was figured. The result shows that linear regression and polynomial analysis can be used to explain this relationship.