Assessing the impacts of environmental change on the hydrology of the Nzoia catchment, in the Lake Victoria Basin.

Abstract

The main objective of this study was to assess the past and potential future environmental changes, and their impact on the hydrology of the Nzoia catchment. More specifically, the study has analyzed the historical climatic (1962-2004) and land cover changes (1973-2001) that have taken place in the Nzoia River catchment in Kenya, and the effect these have had on the hydrology of the catchment. It has also made use of land cover and climate change scenarios for the future to determine the potential effects these will have on the catchment. The Soil and Water Assessment Tool (SWAT) model was used to investigate the impact of land cover and climatic change on streamflow of the study area. The model was set up using readily available spatial and temporal data, and calibrated against measured daily discharge. The land cover changes within the watershed were examined through classification of satellite images and a land cover change model generated the land cover change scenarios for the year 2020. Climate change scenarios were obtained from general circulation models (GCMs) for the period 2010-2039 (i.e. 2020s) and 2040-2069 (i.e. 2050s). The climate change IPCC SRES scenarios A2 and B2 were selected. To this purpose, rainfall and temperature scenarios based on the GCMs CCSR, CSIRO, ECHAM4, GFDL and HADCM3 were superimposed on the calibrated SWAT model.