Climate and anthropogenic footprints implications on the surface and groundwater dynamics on the southern slopes of Mount Kilimanjaro, Tanzania

Abstract

Climate and land use/cover changes impact water resources all over the world. This study aimed at developing a conceptual understanding and management of the impacts of present and future climate change and human activities on surface and groundwater resources on the Kikafu-Weruweru-Karanga (KWK) watershed. The methodology includes simulation of the present and prediction of the future hydrological fluxes and streamflow prediction under changing climate and land use/cover. Calibration and validation of the hydrological model, Soil and Water Assessment Tool (SWAT) showed satisfactory performance (Nash-Sutcliffe Efficiency (NSE)) > 0.50). A total of 22 parameters were used, and Curve number for soil moisture condition II, Baseflow alpha-factor, and average slope steepness were the most sensitive parameters. Future climate data for two Representative Concentration Pathway (RCPs) from Regional Atmospheric Climate Model -22T and Climate Limited Area Modeling 4 models were used. Land use/cover (LULC) maps were generated by classifying time-series (1996, 2006, and 2018) satellite images, selected spatial metrics were used to predict the LULC changes for the next decade using 2018 as a base year. Furthermore, the implications of selected staple crops production over the next decade was predicted. Simulated LULC shows expansion in built-up (by 32.55% and agriculture (by 39.52%) areas from 2018 to 2030, and the forest area is projected to shrink by 6.37%. However, the results suggest that farm size plays a minor role in increasing crop production. Expansion in cultivation land and built-up area attributed to the changes in water yield, surface runoff, evapotranspiration (ET), and groundwater flow. Rock-water interaction chiefly controls the groundwater quality in the presence of HCO3 enrichment and mixed CaNaHCO3 water types. The δ2H and δ18O values confirmed that recycled water is the primary recharge means, and glacier melts on Mt. Kilimanjaro sustains downstream water availability during the dry season. Furthermore, temperatures were projected to increase by 0.2ºC/year, and a decrease in precipitation was projected up to 2100 in both highland and lowland areas. The findings suggested the need to intensify the production per unit area rather than expanding the farm size. Also, improving the vegetation cover on the hillside and abandoned land area could help to reduce the direct surface runoff, and floods recurring in the area. The findings of this study are useful to facilitate sustainable water resources management in the watershed and other watersheds with or without modification.