Future climate change projection and trends under CMIP5 in Lake Tana basin, Upper Blue Nile River Basin, Ethiopia

Abstract Climate change is the long-term fluctuations in the Earth's climate due to either natural variability or human activity. This study is conducted in Lake Tana basin to project future climate change using the Statistical DownSclaing Model (SDSM). The SDSM was used to downscale both temperature and precipitation from Canadian Earth System Model version 2 (CanESM2) Global Climate Models (GCMs) for Bahir Dar, Dangila, Debre Tabor and Gonder synoptic weather stations. The Manna Kendall non-parametric test was then used to examine both the baseline and projected precipitation and temperature trends. The historical or baseline data for downscaling purpose was obtained from National Meteorological Agency (NMA) while large-scale predictor variables were obtained under Climate Model Intercomparison Project Phase 5 (CMIP5) Representative Concentration Pathways (RCPs) 2.6, 4.5 and 8.5 radiative forcing scenarios from the CanESM2 model. The performance of SDSM was evaluated using various statistical methods, such as RMSE, NSE, R and R2. SDSM was not performed well for precipitation projection during calibration and validation period as compared to maximum and minimum temperature. The finding indicated that maximum temperature tends to increase from 1.38°C to 3.59°C under RCP4.5 radiative forcing scenario by the 2080s while minimum temperature is projected to increase up to 5.92°C under RCP8.5 by the end of the 21st century in the basin. On the other hand, precipitation projection did not show consistent pattern in the basin. For instance, precipitation is projected to increase up to 254.88mm in the northern and central parts of the basin but relatively decline up to 199.65mm under RCP8.5 radiative forcing scenarios by 2080s time periods. By considering Mann-Kendal trend test, the baseline and projected mean annual maximum and minimum temperatures shown an increasing trend, while baseline rainfall showed an increasing trend, but projected rainfall showed a decreasing trend at Dangila and Debre Tabor stations and an increasing trend at Bahir Dar and Gonder stations. Therefore, basin or watershed scale climate change adaptation and mitigation strategies should be developed to minimize the negative impacts of climate change.