Land suitability analysis for borehole siting using Geographic Information Systems and Analytic Hierarchy Process in Southern Malawi

Groundwater obtained through boreholes is regarded as a reliable supply of clean, safe water in rural areas. The study aims to assess the suitability of land for borehole siting using Geographic Information System (GIS), Remote Sensing (RS), and Analytic Hierarchy Process (AHP) within Phalombe district of Malawi. Thematic maps comprising eleven criteria; geology, rainfall, lineament density, soil type, slope, land use/cover, drainage density, distance to river, elevation, distance to households, and distance to roads were prepared using satellite data, pre-existing spatial data, and conventional maps. Field observation surveys and an in depth literature review were used to identify these criteria. All criteria and sub-classes were assigned weights using the AHP technique. Weighting was based on relative importance of the criteria for borehole siting. Weighted Overlay Analysis (WOA) was performed in ArcGIS environment. The WOA results were reclassified into five categories: highly suitable, suitable, moderately suitable, unsuitable, and highly unsuitable for borehole siting. The study found that about 29,841.7ha (21.2%) of Phalombe district is highly suitable, 62,685.3ha (44.6%) is suitable, 30,847.2ha (22%) is moderately suitable, 6,928.3ha (4.9%) is unsuitable, and 10,224ha (7.3%) is highly unsuitable for borehole siting. To validate the results, a suitability map was overlaid with 39 existing borehole yield data. About 32 boreholes were correctly classified representing 82.1% accuracy. To evaluate the model's performance, a ROC curve was also created using the borehole yield data. The AUC-ROC curve of 71% indicate good level of accuracy and robustness of methodology. In addition to lowering surveying costs and assisting decision makers in determining the best places to install perennial boreholes, this study supports Sustainable Development Goal No. 6 by ensuring the availability and sustainability of water for all. This study's methodology has proven to be accurate, thus it can be used in comparable studies for other research areas.