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It is anticipated that climate change will impact sediment yield in watersheds. The purpose of this study was to investigate the impacts of climate change on sediment yield from the Logiya watershed in the lower Awash Basin, Ethiopia. Here, we used the coordinated regional climate downscaling experiment (CORDEX)-Africa data outputs of Hadley Global Environment Model 2-Earth System (HadGEM2-ES) under representative concentration pathway (RCP) scenarios (RCP4.5 and RCP8.5). Future scenarios of climate change were analyzed in two-time frames: 2020–2049 (2030s) and 2050–2079 (2060s). Both time frames were analyzed using both RCP scenarios from the baseline period (1971–2000). A Soil and Water Assessment Tool (SWAT) model was constructed to simulate the hydrological and the sedimentological responses to climate change. The model performance was calibrated and validated using the coefficient of determination (R2), Nash–Sutcliffe efficiency (NSE), and percent bias (PBIAS). The results of the calibration and the validation of the sediment yield R2, NSE, and PBIAS were 0.83, 0.79, and −23.4 and 0.85, 0.76, and −25.0, respectively. The results of downscaled precipitation, temperature, and estimated evapotranspiration increased in both emission scenarios. These climate variable increments were expected to result in intensifications in the mean annual sediment yield of 4.42% and 8.08% for RCP4.5 and 7.19% and 10.79% for RCP8.5 by the 2030s and the 2060s, respectively.

Runoff and sediment yield modeling is important in the watershed to alleviate soil erosion and reservoir sedimentation. This paper presents runoff and sediment yield modeling of Kesem dam watershed, which has a drainage area of 2660 km 2. Soil and Water Assessment Tool (SWAT, version 2009) integrated with ArcGIS software (version 9.3) was used to simulate the stream flow and sediment concentration of Kesem dam watershed situated in Awash River basin for the period from 1994 to 2010. The model was calibrated manually by adjusting sensitive parameters using observed data from 2001 to 2006, and validation was done using observed data from 2007 to 2010. The model performance was checked by statistical model performance evaluators such as the coefficient of determination (R 2), Nash-Sutcliffe model efficiency and Percent bias and it shows that the model has a high potential in the estimation of runoff and sediment yield. The test of the model SWAT by simulating the streamflow and sediment concentration was satisfactory. From the generated spatial distribution of runoff and Sediment yield of the Kesem dam watershed, subbasins 12 and 13 were high runoff and sediment yielding sub-basins among the 41 sub-basins. The outputs of this study will be used by water resource managers and decision makers to conserve soil and water in the sub-watershed levels.

Impacts of land use/cover change on water resources are the result of complex interactions between diverse sitespecific factors and offsite conditions; standardized types of responses will rarely be adequate. The knowledge of how land use/cover change influence watershed hydrology will enable local governments and policy makers to formulate and implement effective and appropriate response strategies to minimize the undesirable effects of future land use/cover change or modifications. In this research SWAT model was used for analyzing the land use and land cover change of the watershed and its impact on reservoir sedimentation. The main objective of the research was to model the hydrological processes that will predict the impact of land use/cover changes on soil erosion and sedimentation in the Omo-gibe basin. In this paper the influence of land use changes on catchment's sediment yield is observed. The delineated watershed was divided into 62 sub basins and 372 HRUs by the model. Model calibration and validation was done at Abelti station. In addition to this the model efficiency was checked at this station. Based on this values for coefficient of determination (r²), Nash-Sutcliffe model efficiency (NSE) and percentage of bias (PBIAS) were found to be in the acceptable range for 1990 and 2010 land use land cover maps in both calibration and validation period. To analyze the impact of land use change on sediment yield different comparison criteria were applied. The first was selecting sub basins having higher sediment yield and found around the main course of the river. The second was selecting and analyzing sub basins having lower sediment yield and the third criterion was based on availability of varied land use classes specially sub basins covered by forest land. While analyzing the impact of land use/cover in all criteria using 1990 and 2010 land use/cover map, it shows an increase in sediment yield. SWAT estimated the sediment yield from the watershed to the reservoir for both 1990 and 2010 land use/cover maps. Therefore 1.1 M tons annual sediment load was entered to the reservoir during 1990 and 1.3 M tons annual sediment load was entered to the reservoir during 2010 land use/cover data. This shows that there is 16.57% increment of sediment yield in 2010 as compared to 1990 land use/cover data.

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