DissertationIn Tanzania, irrigated and rainfed agriculture is a key sector of the national economy, and it accounts for more than 75% of the population’s livelihoods. In the Usangu Plains located in the Southern Highlands of Tanzania, little is known about the groundwater recharge dynamics and its interactions with surface water bodies, despite the fact that the area is rich in research initiatives. Consequently, the irrigation schemes and other water user sectors are using groundwater and surface water without a clear understanding of the contribution of each of the two water resources. This study modelled the groundwater-surface water interactions and recharge dynamics in the Usangu Plains. Specifically, the study evaluated the groundwater recharge dynamics in the Usangu Plains using the WetSpass model, analyzed water exchange processes between groundwater and surface water in the Usangu Plains and evaluated the future climate change influence on the groundwater recharge in the Usangu Plains. The GIS-based hydrological WetSpass model was used to evaluate the groundwater recharge dynamics and the future climate change influence on the groundwater recharge while the hydrograph separation techniques were used to analyze water exchange processes between groundwater and surface water. About 13.1% of the mean annual rainfall was found contributing to the groundwater storage. Approximately, due to the lack of groundwater withdrawal information during this study, 0% to 10% of the annual recharge were tentatively considered to be cautiously extracted for economic and domestic use. Except for Great Ruaha River at Msembe, other five rivers manifested a great dependence (more than 90%) on groundwater discharges. Nevertheless, the projected climate change and variations are expected to provoke the decrease of groundwater recharge quantity and distributions within the Usangu Plains. As a result, the surface water volumes will decline as they are used to be sustained by the baseflow. Therefore, in addition to rainwater saving initiatives, effective policies to cope with and mitigate the climate change effects towards groundwater recharge dynamics will guarantee the water availability to meet the future economic, domestic use and crop water requirements.East African Community Scholarship Program via the Inter-University Council for East Africa