Developing suitability maps for rainwater harvesting in South Africa

Dry spells are a direct consequence of spatial and temporal variability of rainfall, and these jeopardise the success of rainfed agriculture by causing crop yield reduction and crop failure in rural South Africa. The potential of rainwater harvesting (RWH) to mitigate the spatial and temporal variability of rainfall has brought about its revival during the last two decades. For planning and implementation purposes, it is critical to be able to identify areas suitable for RWH. The paper presents a methodology that enable water managers to assess the suitability of RWH for any given area of South Africa. Previous methodologies developed to assess RWH suitability recognised the importance of the socio-economic factors but did not incorporate them in their assessment. This non-integration of socio-economic factors is pointed as the main cause of failure of rainwater harvesting projects. In this study, in-field RWH and ex-field RWH suitability maps are developed based on a combination of physical, ecological and socio-economic factors. Model Builder, an extension of ArcView 3.3 that enables a weighted overlay of datasets, is used to create the suitability model, comprising the physical, ecological and vulnerability sub-models from which the physical, the ecological and the vulnerability maps are derived respectively. Results indicate that about 30% is highly suitable for in-field RWH and 25% is highly suitable for ex-field RWH. Details of the proposed method as well as the suitability maps produced are presented in this paper. The implementation of this method is envisaged to support any policy shifts towards wide spread adoption of RWH.