ASSESSMENT OF IMPACTS OF CLIMATE CHANGE AND LAND USE LAND COVER CHANGE ON THE HYDROLOGICAL WATER BALANCE IN THE BLUE NILE BASIN

Abstract

The BN River is one of the most important rivers in Africa and provides water, sustenance, and livelihoods to millions of people living along its banks. It is a critical source of irrigation for agriculture and supports diverse ecosystems. However, climate change and human activities have significantly affected the basin's flow regimes and water availability. This thesis aims to assess the impact of the Land Use and Land Cover Change (LULCC) and Climate Change (CC) scenarios on the BN basin using the Soil Water Assessment Tool (SWAT). Long-term average/static LULC data and streamflow information from four stations within the basin were used to set up the SWAT model. To study the role of LULC on model performance, three modeling scenarios were generated using LULC in the years 2005 and 2015 (dynamic), and 2010 (static). Each model was calibrated and validated using the SUFI-2 algorithm in SWAT-CUP for four streamflow stations. The simulated flow agreed well with the observed flow, with NSE values in the range of 0.67 - 0.84 for calibration and 0.65 - 0.80 for validation. Over the past decade, there has been a noticeable decline in forest cover, with Evergreen, Deciduous, and Mixed Forests experiencing decreases of 12.4%, 29%, and 12%, respectively. The decline in the forest has far-reaching consequences in terms of alterations in hydrological cycles. The future projections of LULC indicate a further decline in different evergreen forests in the coming decades, whereas an increase in deciduous forests is found. Shrubland has the highest estimated percentage of declining features in the basin at around 27% by the year 2065. The expansion of savannas and barren during the same period signifies a shifting landscape influenced by human activities. The average monthly rainfall is expected to increase, which is the reason behind increased surface runoff and streamflow by 2100. The analysis of water balance variables in the BN basin under changing climate conditions indicates that the region will likely experience significant water availability and distribution changes. Our study can aid in promoting sustainable LULC practices, such as conservation and reforestation, to preserve natural habitats and support biodiversity.