Assessment of estimated potential impacts of climate change on the hydrology of Ngerengere river catchment, Tanzania

Global climate change has substantial impacts on local and regional hydrological regime, but general understanding of how hydrological regime is affected by climate change at catchment scale is lacking. In this study, the estimated potential impacts of climate change on the hydrology of Ngerengere River catchment were assessed life rainfall runoff model, HBV model for the catchment was calibrated and validate for impact assessment. Future climate for 2050s (2040 – 2069) and 2080s (2070 - 2099) were downscaled using a statistical weather generator ( LARS-WG ) estimated from outputs of the global circulation model (HadCM3) under A2 emission scenario. The HBV mode; was calibrated and validated using the observed stream flow data at Mgude gauge station for baseline period (1971-2000). The Nash sutcliffe efficiency ( NSE ) of 0.7 and 0.6 was attained during calibration and validation respectively. Downscaling results revealed that LARS-WG performed very well in fitting in future rainfall and temperature data series. The results indicated an increase in minimum and maximum temperature of 0.2 – 2.6 0 C In the 2050s and around 2.7 – 4.4 0 C in the 2080s. The lowest increase in temperature values predicted to be in October and November and the highest increase predicted to occur in May, June and July. Future rainfall is predicted to decrease by 12-37% in April, May, June and July, while rainfall in the remaining months, predicted to increase by 3- 58%. The impacts assessment on the stream flow of the Ngerengere catchment revealed a decline in the mean annual stream flow by 2.1% in 2050s , whereas an increase of up 58% in mean annual stream flow is predicted during the 2080s.