Abstract:
Probable maximum precipitation (PMP) is a characteristic of rainfall at a
particular location that can be used in designing water impounding structures
the resulted extreme floods (PMF) have long been used to design the flood
handling facilities of major dams whose failure might cause loss of life or
extensive property damage. So far the PMP for rainfall stations in Ethiopia have
been estimated by Hershfield statistical method with frequency factor (Km)
determined by the Hershfield's chart. But the chart was originally developed by
using over 2,600 metrological stations ninety percent of which were taken from
USA which might not give reliable estimates for a country like Ethiopia having
different climatic conditions with that of USA. Recent research outputs of
different countries like China, Romania (Desa et al. (2001) and M.N. Desa et
al. (2003)) also showed that the frequency factor (Km) resulting from the
Hershfield's chart is not reliable world over. The objective of this study therefore was to evaluate the frequency factor
obtained from the Hershfield's chart and to provide fresh and reliable estimates
of PMP in Ethiopia using historical rainfall data. In this updating study, annual
maximum 1-day, 2-days and 3-days rainfall data from 64 rainfall stations with
records longer than 15 years found in Blue Nile Basin, were analyzed to obtain
estimates of point PMP using an appropriate frequency factor calculated.
Results of the 24-hours, 48-hours and 72-hours PMP are presented in the
mapped form. In Ethiopia also comparison of the PMP value using the new Km
