Influence of climate variability and land use land cover change on the hydrology and sediment yield in upper Ssezibwa catchment, Uganda

Abstract

Climate variability and Land Use Land Cover (LULC) change influence hydrology and Sediment Yield (SY) in catchments. Globally, over 60 percent of the ecosystem is degraded, over 83% of the terrestrial land surface has been affected by anthropogenic activities over the last fifty years while more than 85% of the area covered by wetlands has been lost since 1700. Variation in rainfall and temperature combined with LULC change have altered the natural habitat, surface runoff (SURQ) and SY leading to siltation of rivers and floods resulting into destruction of property up on the lower part of upper Ssezibwa catchment. This study aimed at assessing the influence of LULC change and climate variability on hydrology and sediment yield in upper Ssezibwa catchment. The specific objectives were to; examine the influence of LULC change on river discharge and SY from 2002 to 2022; determine the influence of variation of interannual rainfall and temperature on river discharge and SY; establish the influence of LULC changes on river discharge and SY for the period 2022-2052; and to assess influence of future variations in rainfall and temperature on river discharge and SY for the period 2022-2052 using SWAT model. The study was anchored in the General Systems Theory that postulates that a morphological/drainage system is composed of different components that are interrelated and an effect on one element affect the entire system. The study used quasi-longitudinal and correlational research designs. Digital Elevation Model, Landsat 7 ETM+ images, meteorological and hydrological data were used. Pearson Correlation Coefficients and Regression analysis were used for data analysis. SWAT model calibration on observed streamflow data (R2=0.85, NSE=0.82, KGE=0.76, PBIAS = -18.5) and validation (R2=0.72, NSE=0.66, KGE=0.66, PBIAS= -19.3) indicate the model is acceptable. Overall accuracy assessment of over 80% and Kappa statistics of 0.82, 0.84 and 0.80 for the years 2002, 2012 and 2022 respectively were satisfactory. Results indicate that LULC change has a statistically significant influence on SURQ, Lateral flow (LATQ), groundwater flow (GWQ), deep aquifer recharge and SY (p = .000, α=0.05). Rainfall has a statistically significant relationship with both discharge and sediment yield (p=0.013, α=0.05) for 2002-2012. Projections indicate that the future LULC change has a statistically significant influence on discharge and SY (p = .000, α=0.05). Projections further indicate that variation in temperature and rainfall for the period 2022-2052 is likely to influence discharge and SY (p = .000, α=0.01) under RCP 4.5 and RCP 8.5 scenarios signaling future flooding within the catchment. The study concludes that LULC changes and climate variability have influenced river discharge and sediment yield in converse proportions in upper Ssezibwa catchment. The study recommends that the central and local governments should enhance the amount of forest cover through afforestation and reforestation initiatives to enhance the ability of the catchment to retain water and controlling sediment loading and surface runoff. In addition, the government should provide public education and awareness about environmental conservation, while watershed protection must be incorporated into development planning.