The study of precipitation distribution is crucial for understanding the hydrology of the catchment. An advanced technology has been developed for precipitation estimation using Microwave and Infrared sensors. The techniques include use of data based on characteristics of cloud tops and its temperature. TRMM is a recently developed such product with high spatial and temporal resolution. Despite of their high resolution, their accuracy needs to be evaluated for proper estimation of precipitation. This book refers to evaluation of use of TRMM data over Nepal. A monthly water balance model developed by 'Thornthwaite' is also simulated with use of these TRMM data for four of the major river basins of Nepal and compared with the measured discharges.