Combined Impacts of Land Use and Cover Change and Climate Change on Streamflow in Large Basins

Abstract

Climate Change (CC) and Land Use and Cover Change (LUCC) may significantly impact water management by exacerbating drought and flood issues. Studying their combined impacts on streamflow in large, regulated basins with limited data remains challenging. This thesis addresses this gap through four objectives. Firstly, a comprehensive literature review on CC adaptation strategies in water management was conducted to investigate their categories, applications, modelling techniques, limitations, and related research gaps. It promoted strategies, such as updating dam operations and Low Impact Development (LID). It highlighted the need to study CC and LUCC combined impacts and incorporate environmental, economic, and social aspects into adaptation strategy assessments. Secondly, to address the scarcity of short-interval streamflow data for hydrologic model calibrations, eight monthly-to-daily streamflow disaggregation methods were assessed at 21 sites in the Nile River Basin (NRB). Interpolation methods excelled, with the 3rd-order mean-preserving method performing best. However, further improvements are needed to better capture daily flow fluctuations. Thirdly, to facilitate hydrologic model development in the NRB, a sensitivity analysis was performed, and five multi-site calibration approaches were tested. It was found that 21 parameters, with soil parameters top-ranked, are significant, and tuning natural subbasin parameters separately from dam regulations improved calibration results. Lastly, the combined impacts of LUCC and CC on streamflow volumes, extremes, and seasonality in the NRB were assessed using naturalized and regulated hydrologic model schemes. CC was simulated using bias-corrected CMIP6 climate models, while LUCC was simulated based on historic trends. Impacts of CC scenarios suggest a range of streamflow changes where their ensemble mean suggests streamflow increases of 8–26% and 7–41% by mid- (and end-of-) century across the NRB. However, the effects of LUCC suggest reductions in streamflow, relatively lessening the CC impact, depending on the CC scenario considered. Accordingly, adaptation strategies should be planned, accounting for such uncertainties.