Effect of Rainfall and Temperature Variability on Streamflow in Nzoia River Basin, Kenya

Nzoia River Basin is one of the regions in Kenya that is highly vulnerable to climate change making its hydrological regimes highly sensitive to rainfall and temperature variability. The aim of this study is to assess the effect of rainfall and temperature variability on streamflow using long-term observational data from nine meteorological stations and two hydrological stations. Trends are indicators to climatic variability and have been analysed using the parametric test of Linear regression and the non-parametric test of Mann–Kendall. Mann-Kendall statistical test was used to identify statistically significant trends in streamflow, rainfall and temperature. Rainfall and temperature exhibit both increasing and decreasing trends in the basin. Streamflow in Nzoia river regions upstream at Webuye (IDA02) and downstream at Rwambwa (IEFO1) has been slowly rising. There is a positive correlation between streamflow and rainfall indicating that streamflow changes in accordance with rainfall. On the other hand, streamflow is negatively related to temperature. This is understandable given that rainfall is the controlling factor for runoff generation; and higher temperatures are a second order effect usually leading to increased evaporation and transpiration. The results of this study will be useful to policy makers in the development of adaptation plans for effective water resources management in the basin.