Influence of Climate Change on Hygrological Drought in the Volta River Basin, West Africa

Abstract

Aerosols’ presence in the atmosphere is known to influence health and weather-related matters. This study investigates the influence of climate change on hydrological drought in the Volta River Basin. The specific objectives were to assess; the potential impacts of climate change on meteorological drought over the basin, the ability of the SWATplus model in simulating the water balance of the basin, and the impact of future climate on hydrological droughts. The datasets used were the observation data (GMFD and CRU) and projected climate dataset (CMIP6 and NEX-GDDP), a digital elevation model, land use and the FAO digital soil map (2003). The Standardized Precipitation-Evapotranspiration Index at 12- and 24-month scales were used to characterise meteorological drought and the Standardized Streamflow Index (SSFI) for hydrological drought at a 12-month scale. The principal component analysis (PCA) and the wavelet analysis were utilised to assess the spatiotemporal patterns of drought using SPEI computed from GMFD. PCA was also performed on the SPEI of the CMIP6 and NEX-GDDP to determine the spatiotemporal patterns of droughts. The SWATplus was calibrated and evaluated using streamflow records at some selected stations. The calibrated model was employed to assess the future climate change impacts using the ACCESS-CM2 output. The SSFI were then computed using the simulated streamflow output as input data. Results showed that NEX-GDDP model captured the climate of VRB accurately as compared to CMIP6. GMFD and CRU perform reasonably well in the stations evaluated. Four drought modes (DM1 – north, DM2 – south, DM3 – east, and DM4 – west) obtained from 12- and 24-month SPEI explained 85 % and 87 % of variance in the VRB. The wavelet analysis reveals cycles with periodicities ranging from 1–16 years in all DMs which corresponded to periods of drought and wetness. Most CMIP6 and NEX-GDDP models were able to capture the spatial patterns of DM1 andDM2. The comparison of the CMIP6 and NEX-GDDP model's ability suggests that bias correction can either improve or reduce the models’ performance in reproducing the drought modes. Some NEX-GDDP models performed better than the CMIP6 counterpart. Climate change assessment in the VRB suggests an increment in temperature (1–4 °C) and a decrease of 0–2.5 mm/year2 in precipitation. Most models projected wetter conditions under SSP5-8.5 in the Near term (2021–2050) and Far term (2081–2100) while more precipitation is expected under SSP2-4.5 in the MF (2051–2080). The calibration of the SWATplus model revealed- good performance in Nawuni, Sabari and Saboba with NSE scores of 0.7, 0.68 and 0.81, R2 of 0.72, 0.69 and 0.91, and Pbias (PBIAS) of -9.1, -1.9 and -18 respectively. Bamboi had a poor NSE (0.101) but good PBIAS (22.7) and R2 (0.52). The validation statistics were satisfactory for all stations. Projected streamflow show significant increase in the future in line with projected precipitation. Projections indicate reduced drought events and intensities under certain scenarios. Consequently, the VRB is expected to face increased flood risks due to projected increasing streamflow, posing significant threats to agriculture, infrastructure, and human well-being. More efforts should prioritize flood risk management in the VRB to address these challenges.