Phetcharinthon Sriviha creator Kazama, So Chairperson Loof, Rainer Examination Committee Morishita, Hideharu Examination committee The Government of Australia Scholarship donor text series technical report th Bangkok Asian Institute of Technology 1999 continuing eng 67 leaves Water balance method is used for the quantification of available water resources potential for planning and decision making. In computing the water balance, whether for a large or small area, the major factor in the equation is evapotranspiration, the problems, encountered in the estimation of evapotranspiration are many, but are often simplified by point estimates. The advent of Geographic Information System (GIS) and Remote Sensing have made it possible to estimate the actual evapotranspiration on single parameter only. The present study deals with the use of GIS and RS in five river basins, in the tropical region with the monsoon. The spatial variation of topography and vegetation coverage are estimated using GIS and A VHRR (Advanced Very High Resolution Radiometer) sensor of NOAA (Nation Oceanographic Atmospheric Administrator) satellite data respectively. NDVI (Normalized Differential Vegetative Index) of each basin for both wet and dry season was calculated from the reflectance of electromagnetic spectrum registered from the A VHRR satellite. The monthly variation of rainfall, runoff and ground water storage change is investigated. The wellknown rainfall-runoff Tank model is used to calibrate the hydrograph and to compute the change in water storage. Putting these values in the water balance equation, monthly actual evapotranspiration is computed. The least square method is carried out with the data set of average NDVI in wet and dry season and actual evapotranspiration estimated from water balance for all five basins to find out a relationship with a best fitted regression line. For those, the logarithmic function is found more suitable for the estimation. This function is applied to all basin to investigate the actual evapotranspiration distribution and produced satisfactory result. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering. School of Civil Engineering Thesis (M.Eng.) - Asian Institute of Technology, 1999 Evapotranspiration Thailand Remote sensing Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B12598 http://203.159.5.9/ait-thesis/detail.php?q=B12598 111199 20260818112725.0