.Reqionalizatlon of Potential Evapotranspiration Prediction for Blue Nile (Abbay) River Basin, Ethiopia

Abstract

Estimation of Potential evapotranspiration is important in Water Resources development program. However, there is no standardized procedure in ungauged stations of the country. In order to address this problem, Regionalization through Multivariate regression models of average monthly potential evapotranspiration is developed for the Blue Nile (Abbay) River basin. Average monthly values of daily PET, is estimated from the Penman-Monteith equation using 13 years (1992-2004) monthly climate data collected from 25 synoptic stations of the National Meteorological services Agency. The periodic seasonal behavior of E, (r) and average monthly temperatures are approximated by Fourier series functions with two harmonics. Regional regression relationships are then developed which relate the E, (r) Fourier series coefficients with the average monthly temperature Fourier coefficients, station latitude, station longitude and station elevation. The regional model developed, £1 .Jr) have satisfactory r, R2 and adj R2 and it is shown to be an improvement over the Priestly-Taylor method (Priestley, and Taylor, 1972), the Turc method (Turc, 1961 ), the Hargraves and Samani method (Hargraves and Samani, 1985), and the regional model also shown to be an improvement over ·other previously developed model (equations) for the basin in particular (Sileshi, 2002).