Crop production in semi-arid sub-Saharan Africa (SSA) is limited by over-reliance on erratic and inadequate rainfall, which often results in yield reduction or total crop failure. The effects of frequent droughts and dry spells need to be circumvented by water conservation. Where rainwater is harvested, research recommendations are based on direct use of the water without relating it to catchment characteristics, climatic conditions and long term storage. A study aimed at predicting sizes of seasonal open surface reservoir based on rainfall and runoff rainwater was conducted from 2012 to 2013 at Ukwe Area, Malawi. The work premised on assessment of land and hydrological factors as they impinge on runoff water storage. Rainfall-runoff relative analysis showed runoff trend following the magnitude of rainfall. Findings showed that runoff water harvested, under the Ukwe area landscape conditions, is linearly related to seasonal rainfall amount with coefficient of correlation of greater than 0.75, demonstrating vitality of rain and timing of rain harvesting for reservoir sustenance. Runoff amount was almost four times that of infiltrated amount, highlighting the fact that drought prone areas can be flood prone as well. Results further demonstrate that weekly reservoir balance using crop, livestock and domestic consumption, and losses through evaporation and seepage, as dry season progresses are critical for reservoir sizing during dam construction or crop field sizing at the onset of dry season.
Key words: Semi-arid, rainwater, reservoir, Malawi, runoff, coefficient.
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