Regional-Scale Groundwater Modelling of Data-Scarce Aquifer Systems in Central Africa Using MODFLOW 6: The Lotikipi Basin (Kenya) and the Northern Basement Transboundary Aquifer (Kenya–Ethiopia)

Groundwater represents the primary freshwater resource for large parts of Central Africa, yet its assessment and management are often constrained by limited hydrogeological data, complex subsurface conditions, and large spatial scales. This thesis develops and applies a regional-scale numerical groundwater modelling framework tailored for data-scarce environments, using MODFLOW 6 as the core simulation tool. The methodology emphasizes conceptual simplification, robust boundary condition definition, use of data from remote sensing acquisitions, and manual calibration aimed at reproducing large-scale groundwater flow patterns rather than point-scale accuracy. The proposed framework is applied to two aquifer systems in Central Africa: the Lotikipi Basin in north-western Kenya, a large sedimentary basin with layered aquifer systems, and the Northern Basement Transboundary Aquifer shared between Kenya and Ethiopia, developed within the framework of a regional groundwater assessment initiative coordinated by IGAD. Despite their differing hydrogeological settings, both case studies face similar challenges related to sparse observations, uncertain parameterization, and regional-scale groundwater management needs. The main terms of the water balance have been quantified for both the systems. For the Northern Basement Aquifer, the calibrated model is further used to investigate future groundwater behavior through transient scenario simulations for the period of 30 years (2025-2055), including climatic stress and changes in groundwater abstraction. These scenarios highlight the sensitivity of regional groundwater levels and transboundary flow dynamics to external pressures. By applying a unified modelling approach to two distinct aquifer types and extending scenario analysis to the transboundary case, this thesis demonstrates the transferability and limitations of regional-scale numerical groundwater modelling under data-scarce conditions, providing insights to support strategic groundwater assessment and management in Central Africa.