Analyzing the Impact of Land use and Climate changes on Soil erosion and Stream flow in the Upper Gilgel Abbay Catchment, Ethiopia.

Abstract

Land use and climate are two main factors directly influencing the hydrological processes of the catchment. Hence, it is crucial to know the combined effects of land use and climate change on catchment hydrology for effective land use planning and water resource management. The Soil and Water Assessment Tool (SWAT) model was used to examine the impact of various land use and climate change scenarios on soil erosion and stream flow in the Upper Gilgel Abbay Catchment. The base reference hydrologic response units (HRUs) for land cover was modified to reflect the trend, conservation and plan based land use scenario definitions and projected to the foreseeable future, 2011-2025.These three plausible land use scenarios were also integrated with 2011-2025 meteorological data from climate local model simulation and their combined effects were evaluated and quantified by comparing SWAT outputs to baseline run (1996-2010). The combined effect of trend based land use and climate change scenario can increase the average annual flow by 5.2% and sediment yield by 29% and would affect soil erosion and stream flow more significantly than other scenario conditions. The trend based land use and climate change alone will increase the flow by 1.7% and 4.7%, and sediment yield by 17.2% and 2.4 %, respectively. On the other hand, the implementation of both plan and conservation based land uses will reduce the increased stream flow and sediment yield caused by the projected climate change scenario; and can be used as an adaptation option for the projected climate change impacts .In general, in all scenario simulation, the flow is more sensitive to climate changes than land use changes however ;soil erosion is likely to be more affected by land use changes than climate changes even if the combined effects of land use and climate change would considerably alters the hydrological behavior of Upper Gilgel Abbay catchment during 2011-2025. Therefore; in the planning of adaptation strategies to climate and land use change impacts on catchment hydrology, it is necessary to consider the combined effects of climate and land use change rather than to simulate their impacts separately.