Development of a methodology for drought frequency analysis using sub-catchments in Zimbabwe

Nyabeze, Washington Rueben Rudo
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The state o f runoff and rainfall data in Zimbabwe is reviewed to determine the extent to which it can be used for drought analysis. The need to augment the available observed records was established. A brief review of literature on rainfall-runoff com puter programs was undertaken. RALFER w as selected for use in this m ethodology mainly because it was available and matched the requirements to model different hydrological regions of Zimbabwe. The selected program was used to model micro catchment runoff using rainfall measurements and a priori knowledge of the catchments. The output was compared with observed figures By application of the same computer program on the same data and with onlv a few modifications to the parameters runoff was generated for the sub-zones. Statistical analysis derived drought frequency graphs and tables This was done on six micro catchments and sub-zones The consistency o f the program was checked by use of different rainfall stations for two of the catchments. The results showed that micro catchment runoff can be easily transformed to sub-zone runoff for hydrological drought analysis. These drought frequency graphs and tables are important for informed w ater resource planning and management They can also be used in environmental management There is scope to apply the methodology to the whole of Zimbabwe but it may be necessary to improve computer software compatibility between the different sources of data and the point of analysis