Assessment of Hydro-climatic Trends and Variability over the Black Volta Basin in Ghana

The present study examines the trends of hydro-climatic parameters over the Black Volta Basin in Ghana. Trend analysis was carried at different time scales (i.e., monthly, seasonal, and annual) from 1961 to 2016. Modified Mann-Kendall (MMK) test, Sen's slope estimates, and Pettit-Mann-Whitney test were applied to compute the existence of a trend, the degree of change, and probable change point, respectively. The results revealed that there are warming trends over the entire Black Volta Basin. Both temperature extremes, i.e., highest and lowest (annual, seasonal, and monthly scale), for upstream and downstream region revealed an increasing trend. The annual rainfall in the upstream region depicted a downward trend, while downstream showed an increasing trend in the Basin. The seasonal trend analysis for rainfall depicted a falling trend (@ Sen's slopes - 0.47 and - 0.69) with a percentage change over the 56 years - 19.66% and - 19.30%, respectively, for upstream and downstream regions during the dry periods. While, the rainy season showed a decreasing rainfall trend (@ Sen's slope - 0.71 and percentage change - 4.41%) for the upstream region and increasing (@ + 0.71 & 4.39%) for the downstream. However, annual rainfall for the sites in the Basin depicted a decreasing trend (@ - 0.88 and - 4.76%) for upstream and an increasing trend (@ + 0.16 with 0.81% change) for downstream region. Annual streamflow revealed an increasing trend (@ + 0.02 with a 1.53% change) over the 43 years for upstream and a decreasing trend (@-0.41 and - 15.04% change) for downstream region at Chache-Bole. Therefore, this study output will be helpful for different stakeholders and policymakers within the Black Volta Basin of the West African sub-region toward improving decisions on water resources management.