Présentations Colloques

Oral Presentation
5.01
Session 5.01: Groundwater resources in a world facing climate change
Oiro Samson
Impact of climate change and human activities on groundwater resources in Kenya- current knowledge and initial findings in Nairobi aquifer system, a strategic aquifer under high pressure
Eastern Africa has been identified as one of the regions at greatest risk globally with regards to the impacts of climate change while also having one of the highest demographic growth rates, e.g. more then 2% currently in Kenya. These combined factors put water resources under very high pressure. One of the most important and strategic groundwater resources in East Africa is the Nairobi volcanic-suite aquifer, which supports the development of the greater Nairobi region. Nairobi metropolitan area has over 6.5 million people and is a major economic centre in East and Central Africa. Currently, the impacts of climate change and human development on the groundwater resources remain uncertain and no conclusive quantitative studies have been carried out so far. The present research is synthesizing the available hydrogeological data relating to the impact of climate change and human activities on groundwater resources. Preliminary data indicate that groundwater demand and borehole drilling is dramatically increasing with population growth and infrastructure development (5 new borehole applications for registration per day). Land use changes are dominated by a reduction of forest cover and open lands and an expansion of urban and built lands estimated to 255 km2 within a span of 50 years. Groundwater levels have generally been decreasing in borehole hot spot areas by 10 – 30 m, following an increase in abstraction together with a possible decrease in recharge resulting from surface sealing. All hydrogeological data, including abstraction, aquifer structure and properties, recharge discharge and groundwater time-series (heads and quality) are being compiled into updated conceptual and numerical groundwater models for the Nairobi aquifer system. Model results will enable a quantitative understanding of the groundwater response to external climate and anthropogenic drivers, as well as their relative importance with regards to groundwater sustainability. This quantitative understanding is key to improving the long-term management of groundwater resources.
United Kingdom