An analysis of long-term rainfall variability, trends and groundwater availability in the Mulunguzi river catchment area, Zomba mountain, Southern Malawi

Annual rainfall series and annual base flow series (1954–1998) derived from the annual river flow series for the Mulunguzi river in Malawi were analysed using the non-parametric Mann–Whitney Pettit and Mann–Whitney–Wilcoxon statistics to detect any trends and variability patterns. A general decline in rainfall, with alternating wet and drier years was detected since 1954. The variation pattern mainly followed the El Nino and Southern Oscillation and the La Nina episodes. Two rainfall change points were detected at 1965 and 1979 after which the rainfall declined.The rainfall trend and variation pattern was evident in the base flow series, indicating a strong correlation between the rainfall and base flow series. This strong correlation means that the Zomba mountain aquifer, the source of the Mulunguzi river mainly depends on rainfall for recharge. Hence all water resources development and planning activities in the catchment area should take into consideration the effects of climate variability on water yield.