ESTIMATION OF WATER BALANCE COMPONENTS USING REMOTE SENSING PRODUCTS IN THE UPPER BLUE NILE, LAKE TANA SUB BASIN

Abstract

Most hydrological and water resource simulation models require relatively accurate estimation of spatially distributed rainfall and evapotranspiration data sets. This research has been conducted with the objective of producing these vital elements of the water balance that can be used as an input to the water resources assessment tools and agricultural water management. Spatially distributed rainfall has been acquired from remotely sensed FEWS data set. Ground validation has been conducted by comparing gridded gauged rainfall data with the remotely sensed FEWS data set. As a result the annual remotely sensed FEWS data set has been found to underestimate the measured ground based data. The annual spatial mean rainfall was underestimated by 33.2% and 35% for 2007 and 2008 respectively. Therefore these biases of the satellite data were adjusted and a spatially distributed rainfall of 1 km grid was obtained. The daily , monthly and yearly evapotranspiration over the Tana sub basin has been computed by Surface Energy Balance System (SEES) algorithm using MODIS land surface products and some ancillary meteorological data with a one km resolution for the entire Lake Tana sub-basin. Open water evaporation of the lake has been estimated with a one km resolution from a remotely sensed data and the spatial averages are 1631.67 and 1623.42 mm for 2007 and 2008 respectively. The change in storage estimated from the Topex/Poseidion Jason-2 lake level variation shows that the lake has increased 290 mm and reduced 301 mm in 2007 and 2008 from the annual average levels of 2006 and 2007 respectivel