Effects of watershed degradation on hydrological functions in the Sondu river catchment.

Abstract

In recent years, forest degradation in the Mau Forest Complex has raised ecological and economic concerns. However, reliable information is largely lacking on the extent of forest degradation and its impact on hydrological services. This has hampered the identification of appropriate intervention strategies. We used geographic information systems and a rainfall-stream flow model to assess the extent of watershed degradation and its effect on hydrological functions in the Sondu River catchment over the past three decades. We found that 30 % of closed canopy forest constituting critical watersheds was converted to farmland between 1973 and 2008. We did not find a significant variation in the mean annual rainfall amounts, but there was a significant variation in monthly rainfall distribution. We found a significant increase in stream flow index. The increase in stream flow index was most likely caused by reduced interception and infiltration of rainfall due to decrease in forest cover. Changes in rainfall distribution and stream flow had adverse impacts on commercial tea production and hydro-electric power generation. Findings of the study provide a basis for developing a framework on payments for environmental services (PES) in order to support watershed rehabilitation.