Investigating human-induced threat to hydrological regime of Lake Chilwa Basin, Malawi

Abstract

The sensitivity of watersheds to climatic and land use alterations remains subject of scientific interest globally. In this study, we analysed hydrological responses to transitions in land use/cover and climate impacts within Lake Chilwa Basin in Malawi, using the soil and water assessment tools (SWAT). Results show that deforestation and cropland expansion largely characterized the basin, particularly in the 2000s decade. SWAT model proved highly effective in analyzing impacts of environmental changes, with indicators such as Nash–Sutcliffe efficiency (Ens), Per cent bias (PBIAS) and ratio of root mean square error to measured standard deviation (RSR) presenting satisfactory values of; 0.88, 0.86; − 11.6%, − 19.8% and 0.34, 0.37 after calibration and validation, respectively. Comparison of exceedance probability between periods provided evidence of increasing runoff of up to 11% and subsequent declining baseflows linked to deforestation; irrespective of climate influence which portrayed a decrease–increase–decrease decadal impact on streamflow. The study further shows that forest vegetation tended to escalate evapotranspiration (ET), although the forest role of reducing runoff and enhancing groundwater recharge outweighed the ET effect. Since most watersheds in the basin remain significantly deforested, the threat of increased runoff leading to flooding and declining dry-seasonal river flows is certain.