Application of expert knowledge based multi-criteria evaluation MCE process to select suitable areas for water harvesting systems in Sub-Saharan Africa, a case study of Tanzania

The main challenge to agricultural development in the drylands of Sub-Saharan Africa (SSA) is scarce and erratic rainfall, and so water resources are becoming increasingly insufficient to meeting the ever increasing demands. Water harvesting has proved to be an appropriate means to guarantee the sustainability of the water resources for domestic use and agricultural production. However, despite the existence of these few successful initiatives in different parts of the world, they only remain localized, and therefore the big challenge is to find ways in which these can be scaled up in both space and time so as to increase agricultural productivity. This study attempts to apply an expert knowledge base Multi-criteria evaluation (MCE) process to identify appropriate suitable sites for Water harvesting to upgrade rainfed agriculture in these drylands of SSA, a case study of Tanzania. Different parameters such as rainfall, topography, landuse/ land cover, soil and vegetation characteristics which are important for runoff generation were identified. Both remote sensing and ancillary secondary data were used for runoff generation potential assessment. The indexing (assigning of weights) method was used for the analysis of runoff potential. However, the process to decide on the final suitable areas for water harvesting involved the assessment of alternatives in which case the Analytical Hierarchical Process (AHP), a decision support system, was used to rank and weigh different alternatives. Different parameters influencing the selection of suitable sites for water harvesting systems included the runoff potential, slope, proximity to roads and settlements, and arable lands and soil-scape units. These criteria were complimented by both expert and indigenous knowledge. The ranking of these alternatives facilitated the generation of final suitable maps for different water harvesting systems (macro and micro-catchments) which would in future be used as the basis for planning further water harvesting in the region. The methodology could used be replicated to areas with SSA to improve water productivity for agricultural production.