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).
