Assessment of The Impact of Climate Change on Surface Hydrological Processes Using GIS Based Hydrological Model (Case Study of Omo Gibe River Basi, Ethiopia).

Abstract

Climate Change impact are assessed by the General circulation Model. GCM output simulation have systematic errors called Bias ,which need to be corrected The bias correction of precipitation and temperature leads to reasonable result in hydrological impact studies . Physicalbased, semi-distributed hydrological models, ArcSWAT, was utilized to simulate hydrological responses to land use and climatic changes. Stream-flow data at the outlet of the watershed was utilized to analyze seasonal stream flow variability. The performance of the model has been evaluated through sensitivity analysis, calibration, validation and uncertainty analysis. The case study was applied on Omo-Gibe river basin, Ethiopia. Among the most sensitive parameters governing runoff generation process, in the studied Basin, were CN2, ALPHA_BF and ESCO etc . The overall evaluation indicated that the SWAT model satisfactorily simulates river flows in the study catchments with limited data availability and where global spatial data are appropriate. By using input data used for SWAT model calibration, and validation, whereby the gauged flows in the Gojeb and Great Gibe water sub-catchments are the calibration targets. Calibration and validation processes were undertaken using the Parasol and manual methods of SWAT2005, and the SUFI-2 methods of SWAT-CUP. Time series plots, as well as statistical measures, such as the Nash-Sutcliffe efficiency (NSE) and the coefficient of determination (R 2 ) between observed and simulated stream flows are computed on daily or monthly time scales and indicate a goodperformance of the final calibrated SWAT model. In monthly time scales Great Gibe Abelti gauging station the R 2 was found to be 72.4%,and NSE. = 62.6 % for calibration and the R 2 was found to be 68.1%,and NSE. = 68 % for validation. This shows the simulation’s very good correlation with the gauged flow.SUFI-2, algorithms gave good results in minimizing the differences between observed and simulated flow in the Great Gibe sub-basin. The p-factor and r-factor computed using SUFI-2 gave good result performance more than 60% of the observed and simulated data under calibration and validation. The studies show that there is an overall increasing trend in annual temperature and significant variation of monthly and seasonal precipitation from the base period 1985 to 2005 level. The results indicate that the annual potential evapotranspiration (PEV) will show increasing trend for both future climate scenario. The study makes the recommendation that SWAT model can be effectively used for assessing the water balance components of a river basin