Groundwater resilience to climate change in Africa.
This research project has examined the resilience of groundwater to climate change in Africa; an area of science that has been under-researched, but has much relevance for the formulation of climate adaptation policies. There are several outcomes from the research:
A series of quantitative groundwater maps for Africa- the first of their kind. These indicate the wide variation in groundwater resources across the continent. For much of Africa, carefully sited and constructed boreholes will be able to sustain rural handpumps.The potential for shallow boreholes yielding greater than 5 l/s is not widespread across Africa, although smaller yields of 0.5 to 5 l/s will be easier to find. Large groundwater stores in the major sedimentary basins, which can accommodate high yielding boreholes, are often far from population centres and associated with deep water-levels.
<i>New data from focused groundwater case studies. </i>Three case studies were undertaken to gather new data on groundwater and climate change in Africa:
Detailed sampling in West Africa from hand-pumped boreholes abstracting shallow (less than 50 m deep) groundwater indicates significant resilience to climate variability across the range of climate zones sampled (mean annual rainfall 400–2000 mm). The mean residence of groundwater in shallow aquifers was approximately 20–70 years and therefore well buffered against short term variations in climate. The residence time of shallow groundwater in weathered basement rocks was found to be similar to the residence time in sandstones, indicating that weathered basement can contain considerable volumes of groundwater which moves slowly because of the low permeability.
A study of higher yielding supplies from crystalline basement rocks in Uganda and Tanzania indicates that sustainable larger supplies are often associated with a thick regolith (often including alluvium) over weathered basement rocks, and that yields of more than 1 l/s maybe available in approximately 35% of effectively sited boreholes in these areas. Enhanced groundwater storage in this aquifer environment is of particular importance in semi-arid regions (e.g. Dodoma, Tanzania) where significant recharge occurs episodically in association with extreme climate events a few times or less per decade.
Detailed analysis of data on water use in Ethiopia found that both wealth and the seasonality of water access are important drivers of domestic and productive water use, probably due to higher collection times in the dry season and the labour shortages faced by poor households. Policy responses in the water sector need to centre on: extending reliable services to reduce collection times, even where coverage statistics may look positive; safeguarding health and livelihood needs, especially at critical times of year; and enhancing the storage and transport facilities of poorer households.
It is clear from this research that groundwater possesses a high resilience to climate change in Africa and should be central to adaptation strategies. Increasing access to improved groundwater sources based on handpumps is likely to be highly successful. However, building strategies that depend on the availability of widespread higher reliable yields from groundwater is likely to be problematic.
MacDonald, A.M.; Bonsor, H.C.; Calow, R. C.; Taylor, R. G.; Lapworth, D. J.; Maurice, L.; Tucker, J.; Ó Dochartaigh, B. É. Groundwater resilience to climate change in Africa. British Geological Survey, Nottingham, UK (2011) 25 pp. [British Geological Survey Open Report, OR/11/031]