Assessment of Effects of Climate Change on the Stream flows Upstream of Nyumba ya Mungu Reservoir: the case of Kikuletwa and Ruvu Catchments

Future climate projections of Global Climate Models (GCMs) under different scenarios are usually used to develop climate change mitigation and adaptation strategies. Problem of reduced streamflows, increase in temperature and evapotranspiration in Kikuletwa and Ruvu catchments needed to assess effects of climate change of streamflows (IUCN, 2009). Simulation of future climate change was carried out using six General Circulation Models (GCMs) namely are GFDLCM2.1, Ivmwc3.2NED, HadCM3, HadGEM1, and ECHAM5 based on A2 scenario of Special Report on Emission Scenarios (SRES). LARS-WG which is a stochastic weather generator used as downscaling tool of GCMs outputs (predictors). GCMs simulation results indicated that there will be 16-18% increase in mean rainfall in the year 2046 2065 as compared to year 1980-1999. Likewise, temperature simulation showed an increase trend by 20 C in average, by 2050s. In case of streamflows projection shows that basin (Kikuletwa and Ruvu catchment) will face reduced annual streamflows by 5.3% as a result of climate change impacts. Looking at individual catchment Ruvu catchment will have a decrease of streamflows by 24.3% as opposed to Kikuletwa catchment which showed an increase in streamflows by 10.47%. However, 30.90 m3/s of average low flow is expected in November-January season while average peak flow of 82.20 m3/s is projected to occur in April-June season in the study area. Also, there is a slight decrease by 0.3m3/s from JASO season (31.2m3/s).