Modeling projected impacts of climate and land use/land cover changes on hydrological responses in the Lake Tana Basin, upper Blue Nile River Basin, Ethiopia

Abstract

This study is being conducted in Lake Tana Basin, Upper Blue Nile River Basin, Ethiopia. This work focuses on the assessment of the separate and combined impacts on water balance components of both climate and LULC change. For calibration, validation and uncertainty analysis, the Soil and Water Assessment Tool (SWAT) was used in conjunction with the IPEAT (Integrated Parameter Estimation and Uncertainty Analysis Tool) package. To produce high resolution future climate data from CanESM2 GCM that could be used for impact assessment, the Statistical DownScaling Model (SDSM) was used while the future LULC prediction was generated using Cellular Automata-Markov Chain model. The hydrological response of the basin was assessed by dividing the future time periods in to 2020s (2011–2040), 2050s (2041–2070), and 2080s (2071–2100) through incorporating three scenarios, such as LULC change alone, climate change alone and combined climate and LULC change. The prediction of the LULC change using the CA-Markov chain model indicates that cropland, tree cover, and built-up areas are likely to increase by 2020s, 2050s, and 2080s at the expense of grassland and shrub cover areas, leading to an increase in evapotranspiration, baseflow and streamflow conditions in the basin. By considering basin average, the climate prediction result suggests an increase in both Tmax (up to 2.14 °C) and Tmin (up to 3.2 °C) temperatures, whereas precipitation would increase by up to 25% in the basin. The results show an increase of evapotranspiration by up to 0.84%, 59.8% and 55.5% under LULC, climate and combined climate and LULC change by the end of the 21st century under RCP8.5 compared to the baseline period, respectively. Furthermore, both stream-flow and lateral flow are projected to increase by up to 12.85% (9.9%), 28.5% (20.03%) and 26.4% (29.12%) under LULC, climate and combined climate and LULC change scenarios, respectively. As predicted, the shift in magnitude in RCP8.5 emissions is greater than RCP2.6 and RCP4.5. The impacts of climate change on water balances are relatively higher than the combined effects of changes in climate and LULC. Future LULC shifts, on the other hand, change comparatively offsetting hydrological components. In order to devise local-scale adaptation and mitigation strategies, the inclusion of predicted climate and LULC change for hydrological impact studies, is therefore, very useful.