A regression analysis for annual precipitation as a dependent variable of altitude is done to evaluate precipitation in the Gina River catchment. This shows the best results for a second order polynominal fit where 90 % of the annual rainfall can be explained by elevation (see figure). Transferring the correlation analyses to the Gina River catchment results in precipitation values ranging from 1530 mm/a (about 2400 m a.s.l.) in the lowlands to 1580 mm/a (at 2780 m a.s.l.). The Mountain tops show values around 1520 m/a (about 3200 m a.s.l.).

Addition to the picture: Results of the assessment of the landscape factor precipitation; left: Correlation between altitude and annual precipitation for the meteorological stations in the Abaya-Chamo Basin; right: recurrency interval of daily rainfall at Chencha weather station in the Gina River catchment in 2001 and at 2680 m a.s.l.

Variability

A magnitude-frequency analysis is done to show the rainfall variability in the Gina River catchment. This analysis shows that rainfall events of

• more than 50 mm per day have a recurrence interval of 1000 days;
• about 30 mm per day have a recurrency interval of 3,5 years;
• less that 10 mm per day have a recurrency interval of 10 days (Beck et al. 2004, 35/36).

The results of the soil survey are presented on the next page.