Modelling the impact of land use management on water resources in a tropical inland valley catchment of central Uganda, East Africa.

A combination of climate change, food demand, population growth, and other driving forces are causing land use and land cover change (LULC) in wetlands of Sub Saharan Africa (SSA). This has a profound effect on water resources, thus it is imperative that such consequences arising from these changes are predicted accurately to support land use management. For that, local scale studies are required to understand the system and to perform scenario analysis. The focus of this study was on small scale inland valleys which are common in SSA. The impact of LULC on the hydrological processes in a tropical inland valley was investigated. A hydrological response unit (HRU)-based (ArcSWAT2012) and a grid-based setup (SWATgrid) of the Soil Water Assessment Tool (SWAT) model are applied. Good model performance was achieved after calibration and validation with daily discharge (R2 and NSE > 0.7 for both model setups). Annual water balance indicates that 849.5 mm representing 65% of precipitation is lost via evapotranspiration. Surface runoff (77.9 mm) and lateral flow (86.5 mm) are the highest contributors to stream flow in the inland valley. Four land use management options are developed in addition to the current land use system, with different water resources conservation levels (Conservation, Slope conservation, Protection of headwater catchment, and Exploitation). There is a strong relationship between the first three management options with decreasing surface runoff, annual discharge and water yield while the fourth option will increase annual discharge and total water yield. This suggests that if poor management and increasing exploitation of the inland valleys persist, the availability of water resources for human consumption and plant growth will decrease. This study contributes to improving the scientific knowledge on the impact of land use change on hydrological processes in the catchment-wetland nexus to support sustainable water resources management.

Modeling the effect of land use and climate change on water resources and soil erosion in a tropical West African catch-ment (Dano, Burkina Faso) using SHETRAN.

This study investigates the effect of land use and land cover (LULC) and climate change on catchment hydrology and soil erosion in the Dano catchment in south-western Burkina Faso based on hydrological and soil erosion modeling. The past LULC change is studied using land use maps of the years 1990, 2000, 2007 and 2013. Based on these maps future LULC scenarios were developed for the years 2019, 2025 and 2030. The observed past and modeled future LULC are used to feed SHETRAN, a hydrological and soil erosion model. Observed and modeled climate data cover the period 1990-2030. The isolated influence of LULC change assuming a constant climate is simulated by applying the seven LULC maps under observed climate data of the period 1990-2015. The isolated effect of climate scenarios (RCP4.5 and 8.5 of CCLM4-8) is studied by applying the LULC map of 1990 to the period 1990-2032. Additionally, we combined past modeled climate data and past observed LULC maps. Two chronological and continuous simulations were used to estimate the impact of LULC in the past and in the future by gradually applying the LULC maps. These simulations consider the combined impact of LULC and climate change. The simulations that assumed a constant climate and a changing LULC show increasing water yield (3.6%-46.5%) and mainly increasing specific sediment yield (-3.3%-52.6%). The simulations that assume constant LULC and climate as changing factor indicate increases in water yield of 24.5% to 46.7% and in sediment yield of 31.1% to 54.7% between the periods 1990-2005 and 2006-2032. The continuous simulations signal a clear increase in water yield (20.3%-73.4%) and specific sediment yield (24.7% to 90.1%). Actual evapotranspiration is estimated to change by between -7.3% (only LUCC) to +3.3% (only climate change). When comparing observed LULC and climate change alone, climate change has a larger impact on discharge and sediment yield, but LULC amplifies climate change impacts strongly. However, future LULC (2019-2030) will have a stronger impact as currently observed.