IMPLICATION OF REPPRESENTATIVE CONCENTRATION PATHWHAYs ON ARJO-DIDESSA CHATCHMENT, UPPER BLUE NILE BASIN, USING MULTIPLE CLIMATE MODELS

Abstract

Climate change impact is becoming a global agenda and its impact can be significant on water resources system. Therefore, this study has evaluated the impact of climate change on stream flow of Arjo-Didessa catchment, Upper Blue Nile basin. The projection of future climate variables was done by using the selected four climate models namely HadGM2-ES, MPI-ESM-LR, ICHEC-EC and CM5A-MR under RCP4.5 and RCP8.5 scenarios. The projection analysis was done for the medium future time period (2041-2070) by taking 1971- 2000 as a base line period. HEC-HMS rainfall runoff model was found suitable for stream flow simulation for the study area. It reasonably captured the observed hydrograph pattern and volume. The pattern of the simulated rainfall from the three climate models resembles the gauge rainfall. However, the bias was found too significant to ignore. As such bias correction was applied. Annual rainfall in 2041 to 2070 will likely decrease by 0.36% to 16% for RCP4.5 and by 0.5% to 21% for RCP8.5 whereas annual evapotranspiration will increase by 3% to 5% for RCP4.5 and by 4% to 7% for RCP8.5. Mean maximum temperature will increase up to 1.1 for RCP4.5 and up to 3.16 for RCP8.5 scenario. However, the minimum temperature will increase up to 1.24 under RCP4.5 and up to 1.5 under RCP8.5. The climate variables change is likely to have a significant impact on the stream flow volume. Annual flows will likely decrease by 1% to 3% for most models under RCP4.5. Seasonal flow will increases by 3% to 5% and increase by 11% to 18% in Kiremt (rainy) season for RCP4.5 and RCP8.5 respectively while it may decrease up to 5% in Belg (small rain) season under RCP4.5 scenario. A significance difference in projecting annual flow was showed for CM5A-MR and ICHEC-EC for RCP4.5 and RCP8.5 respectively. Unlike other models, annual flow for CM5A-MR under RCP4.5and ICHEC-EC under RCP8.5 will likely increase by 2% and 9% respectively while the other model in both scenario showed decreases. Generally it is observed that, there will be a net annual reduction of stream flow up to 3% in Arjo- Didessa catchment in the medium future period. Most climate models fully