Influence of variability of rainfall on flow regimes and water resources in Mkomazi valley

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University of Dar es Salaam
This research investigates the link between the variability of annual run-off and the corresponding annual rainfall by using a headwater catchment of Mkomazi sub catchment located in the South-eastern part of Pangani river basin (Figure 1.1). Precipitation from five rainfall stations has been investigated with the intention of computing areal rainfall of Mkomazi sub-catchment, which was required in the study. Shume Forest rainfall station with long record (96 years) was used as an index station to study the long-term temporal variability of rainfall over the Upper Mkomazi catchment. It has been observed that the mean annual rainfall has declined since the beginning of this century and that this low mean was maintained up to the first half of the 1990's decades. However, the linear trend of the decline is found to be not significant. The flow series of Mkomazi at Gomba station was extended from a long time series of areal rainfall determined for the river sub-catchment using a Monthly Water Balance Model (VUBMOD). This enabled the investigation of the long-term variation of flow regimes. The analysis of the constructed flow showed that there is an amplified variability of flow during the main rainy season (March - May). On the other hand, it was observed that flows during the short rain season depend very much on the rainfall of October. The low flow regime (July - September) is less affected by variability of seasonal rainfalls. The study has also shown that the run-off variability was amplified compared to the rainfall variability. The analysis on the timing of rainfall showed that March to May rainfalls are significantly important for the total flow to the river during the main rainy season, though February rainfalls are the most significant cause of high flows during the main rain season as they determine the losses.
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Rain and rainfall, Tanzania, Mkomazi valley
Kashimbiri, N. (1999) Influence of variability of rainfall on flow regimes and water resources in Mkomazi valley, Masters’ dissertation, University of Dar es Salaam. Available at (