Rainfall and Streamflow Variability in Ghana

The objective of this research is to investigate the variability of rainfall and streamflow over Ghana. Analyses of rainfall shows larger daily variability and maxima amounts in the southern coastal belt than in either the middle or northern parts of the country. The high variability in rainfall at the coast is associated with sea surface temperatures (SSTs) changes over the Guinea coast. This is related to the evolution of the cold tongue over the Atlantic during the rainfall season. The results indicate that the extreme rainfall events occur as single events, but there are occasions when they occur sequentially, and some of these events could continue for more than 5 days. We note that the average SSTs over the equatorial Atlantic favor the occurrence of extreme rainfall over the coastal and middle belt, while relatively cold SSTs favor the occurrence of extreme rainfall events in the northern belt.;This study also shows the presence of eastward moving convective signals which are associated with Kelvin waves that impact the rainfall in spring over Ghana. Kelvin waves account for ~70% of the extreme rainfall events during boreal spring compared to 25%-35% in summer. The reason for this is that the rainfall in southern Ghana peaks in spring when the frequency of propagation of these waves is the highest.;Analysis of streamflow and rainfall suggested that both rainfall and streamflow exhibit a bimodal pattern. Although the peak in rainfall occurs during the major season, the peak in streamflow occurs during the minor season. Extreme rainfall events are more associated with flooding in the rivers than continuous non-extreme rainfall events. Additionally, we note a decreasing trend in rainfall and streamflow over the southern part of Ghana. But, the decrease in streamflow is larger than for the rainfall. It is to be noted, however, that the draw of water from the two rivers by the communities for domestic and irrigation use are very difficult to quantify and could be the cause of the disparity between the trends in rainfall and streamflow.