Exploratory analysis of rain days in central Sudan

The changes in six rain-day categories occurring since the 1940s have been explored in central Sudan, considering two case studies representing important productive agricultural regions under semi-arid rain-fed and arid irrigated schemes. Drought conditions have persisted in Kosti (arid) in the form of a decline in rain-day frequencies, with significant trends in trace, weak and moderate falls. El Gedaref (semi-arid) exhibited both positive and negative trends, though significance characterizes the sequences of trace (falling) and weak and very strong (both rising) falls. The total annual rainfall in El Gedaref behaves depending solely on the heaviest falls contrary to Kosti, the annual values of which follow five fall categories, but with the heaviest events also have the strongest strength. Trace events occur more frequently in the arid area than in the semi-arid one, whereas weak to very strong events have opposite behaviour. Although El Nio-Southern Oscillation is one potential forcing of the variability of rainfall events, especially in Kosti, the paper arguably proposes a complex combination of factors at smaller scale that may also contribute to the large non-uniformity in rainfall patterns between the two areas, including local moisture recycling and convective activity, natural and anthropogenic aerosol loadings in the atmosphere and influence of the Ethiopian highlands.