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
separatel
