The Nairobi volcano-sedimentary regional aquifer system (NAS) of Kenya hosts >6 M people, including 4.7 M people in the city of Nairobi. This work combines analysis of multi-decadal in-situ water-level data with numerical groundwater modelling to provide an assessment of the past and likely future evolution of Nairobi’s groundwater resources. Since the mid-1970s, groundwater abstraction has increased 10-fold at a rate similar to urban population growth, groundwater levels have declined at a median rate of 6 m/decade underneath Nairobi since 1950, whilst built-up areas have increased by 70% since 2000. Despite the absence of significant trends in climatic data since the 1970s, more recently, drought conditions have resulted in increased applications for borehole licences. Based on a new conceptual understanding of the NAS (including insights from geophysics and stable isotopes), numerical simulations provide further quantitative estimates of the accelerating negative impact of abstraction and capture the historical groundwater levels quite well. Analysis suggests a groundwater-level decline of 4 m on average over the entire aquifer area and up to 46 m below Nairobi, net groundwater storage loss of 1.5 billion m3 and 9% river baseflow reduction since 1950. Given current practices and trajectories, these figures are predicted to increase six-fold by 2120. Modelled future management scenarios suggest that future groundwater abstraction required to meet Nairobi projected water demand is unsustainable and that the regional anthropogenically-driven depletion trend can be partially mitigated through conjunctive water use. The presented approach can inform groundwater assessment for other major African cities undergoing similar rapid groundwater development.
Bibliographical noteOpen Access via the Springer Compact Agreement
We acknowledge the Royal Geographical Society (with IBG) Environment and Sustainability Research Grant for supporting the fieldwork activities, and The World Bank/Aurecon AMEI Limited for supporting model scenarios simulations. We are also grateful to the Kenyan Water Resources Authority (WRA) and the University of Aberdeen for jointly supporting Samson Oiro’s PhD scholarship. We warmly thank WRA staff involved in data compilation and acquisition as well as the WRA offices (Nairobi and Kiambu Office) for providing the borehole completion reports and abstraction records. We thank three reviewers for their constructive comments which contributed to improve the final manuscript.
- Long-term groundwater records
- Aquifer depletion
- Hydrogeological conceptual model and numerical modelling
- Nairobi aquifer system
- Groundwater monitoring
- Conceptual model
- Numerical modelling
- STORAGE CHANGES