A DISSERTATION SUBMITTED TO DEPARTMENT OF GEOGRAPHY AND ENVIRONMENTAL STUDIES, ARBA MINCH UNIVERSITY COLLEG E OF SOCIAL SCIENCE AND HUMANITIES, IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DOCTOR OF PHILOSOPHY IN GEO GRAPHY AND ENVIRONMENTAL STUDIES: SPECIALIZATION IN ENVI RONMENT AND NATURAL RESOURCES MANAGEMENT

Abstract

Climatic and land use/land cover (LU/LC) changes exert significant influences on hydrological processes across various spatial and temporal scales. The Gilgel Gibe catchment in southwest Ethiopia serves as a crucial water source for diverse socio-economic and environmental purposes. However, this catchment is undergoing rapid land use/land cover (LU/LC) as well as climatic changes, which are profoundly affecting its hydrological processes and water resources. This study investigated the combined effects of LU/LC and climate change on the hydrological processes within the Gilgel Gibe catchment. The Soil and Water Assessment Tool (SWAT) model was employed to simulate hydrological responses under three LU/LC scenarios (2021 baseline, 2039, and 2057) and two Representative Concentration Pathways (RCPs) for climate change (4.5 and 8.5) from 1991 to 2099. The interpretation and classification of Landsat imagery, along with the results from field observations, have revealed substantial LU/LC alterations between 1991 and 2021. There has been an expansion of cultivated land and built-up areas, while forest cover, grazing land, and shrubland have declined. Factors such as human population growth, agricultural land expansion, built-up area expansion, land degradation, deforestation and inadequate conservation practices are driving these changes. Both LU/LC and climate change markedly influence the catchment’s hydrological processes. Land use/land cover change projections showed an increase in surface runoff (2.02%-4.09%) and water yield (2.62%-3.23%), but a decrease in groundwater recharge (0.09%-0.63%) relative to the baseline. Climate change is anticipated to exert a more substantial impact, with the most pronounced reductions in surface runoff, groundwater recharge, and water yield expected under the RCP8.5 scenario. The combined effects of LU/LC and climate change appear to be additive, intensifying these trends and posing potential risks to water availability and the sustainability of resources in the catchment. This indicates the Gilgel Gibe catchment’s vulnerability to both LU/LC and climate change, with anticipated alterations to the hydrological processes. This study emphasizes the pressing need for a coordinated approach to address the combined effects of LU/LC changes and climate change within the Gilgel Gibe Catchment. As such, policymakers and stakeholders ought to focus on enhancing agricultural productivity through improved inputs and conservation practices, developing alternative income sources for sustainable livelihoods, and strengtheningstakeholders in sustainable management practices and establishing climate-resilient environment is vital. Future research should evaluate the impacts of land degradation on hydrology and sedimentation, as well as the role of vegetation in soil conservation. These activities are critical for the environmental sustainability of the catchment and the welfare of the communities that rely on it. Collective efforts are essential to ensure the catchment’s environmental sustainability and the prosperity of the communities it supports ecosystem conservation via reforestation and afforestation practices. Moreover, e