An assessment of the hydrologic impacts of groundwater abstraction over Uganda

Abstract

Groundwater is widely acknowledged to be an important source of drinking water in Sub-Saharan Africa and plays a critical role in the recognition of human rights to water. Uganda is currently experiencing growing pressure on the available water resources caused by increasing water demand for agricultural, domestic, and industrial consumption as well as climate variability. This has led to increasing groundwater abstraction across the country leaving many areas at risk of water shortages. However, there is still inadequate scientific evidence about the hydrologic impacts of groundwater abstraction in Uganda. . To address this knowledge gap, the specific objectives of the study were to 1) examine the status of the groundwater supply network in Uganda, 2) examine the spatial and temporal variation in groundwater abstraction over Uganda, and 3) assess the impacts of groundwater abstraction on selected hydrologic variables. Data on groundwater supply points was sourced from the Water Supply Database from the Ministry of Water and Environment (MWE) and information on location, year of commissioning, funding sources, ownership, and the total number of people supplied was availed. These data were used to estimate groundwater abstracted across the country disaggregated by the four Water Management Zones (WMZs) over Uganda i.e. the Upper Nile, Kyoga, Albert, and Victoria WMZs. The study also used a calibrated Community Land Model (CLM4) hydrological model to evaluate the hydrologic impacts of increased groundwater abstraction over Uganda. Results show that the Upper Nile WMZ (especially in the districts of Yumbe, Arua, Adjumani, and Nebbi) and the Kyoga WMZ (especially in the districts of Tororo, Apac, and Kamuli) are abstracting more groundwater (between 2,600,000 to 3,200,000 liters per day respectively) as compared to the Albert and Victoria WMZs. This may be attributed to increased water demand resulting from increased refugee inflows from neighboring countries and increasing population. The study results also show that increasing groundwater abstraction leads to a decrease (increase) in base flow, water table depth, and surface runoff (evaporation, groundwater recharge, soil moisture, and infiltration). For instance, if the current groundwater abstraction rate is increased by 100%, baseflow, water table depth and surface runoff decreased by 0.0012cm/month, 0.045 m, and 0.00075 cm/month respectively, while the evaporation, groundwater recharge, soil moisture and infiltration increased by 0.0035 cm/month, 0.010 cm/month, 0.012 m/month and 0.024 cm/month respectively. The study, therefore concludes that Kyoga WMZ had the highest number of groundwater supply points drilled over Uganda and groundwater abstraction was more pronounced in Upper Nile and Kyoga WMZs in the districts of Yumbe, Arua, Nebbi, Lamwo, Adjumani, Tororo, Iganga, and Kamuli.