Human influence on water availability variations in the upper Ewaso Ng’iro river basin, Kenya

Upper Ewaso Ng’iro catchment is located in Eastern Africa – a water-scarce region. Streamflow is in decline in the catchment despite the pattern of increasing amounts of rainfall in the East African region. This study explored historical human-water interplays to understand the coevolution of hydrological systems and societal development and to identify the dominant features contributing to water deficits and water-related conflicts in the lowland zone of the catchment. A socio-hydrological conceptual framework was used to mimic and explain the two-way coupling between human and hydrological systems. The results show that the dominant features that have likely contributed to changes in lowland streamflow and water-related conflicts include: population growth, land use/cover changes, and economic dynamics. The dry season flows have been extremely reduced with a 100% reduction observed in the month of February especially between 2010 and 2020 while the wet season flows have increased by about 10% and 15% in the upland and midland zones respectively. The decreasing trends in the streamflow against increasing amounts of rainfall emphasize the direct role humans have on catchment water availability. East Africa being a water-scarce region, there is a need to shift the focus from ‘the sustainable natural flows perspective’ to ‘the amount of water retained during wet seasons perspective’, improving land conservation activities to increase water infiltration during wet seasons, and the need to bring all stakeholders together for collective understanding.