Groundwater's Climate Resilience

Global climate change is expected to affect both temperature and precipitation across Africa. Temperatures are expected to rise by 3-4°C, increasing evapotranspiration rates, whilst mean annual rainfall is predicted to vary by up to ±10-20% (Carter and Parker 2009). Both inter-annual and seasonal variability in rainfall patterns are likely to increase in a region already characterized by variable rainfall (Carter and Parker 2009). Extreme weather events such as flooding and drought are set to intensify (Kusangaya et al. 2013). All of this contributes to making Africa’s water supply even more difficult to manage. Increasing the reliability of supply is key. Africa’s agriculture is particularly vulnerable to climate change due to its widespread reliance on rain fed agriculture, its extreme intra and inter-season climate variability and recurrent dry and wet seasons, coupled with its extensive poverty and consequent low ability to adapt (IPCC 2014b).

More than 95% of food grown in Sub-Saharan Africa is rain-fed. Climate change, therefore, threatens food security because surface water supplies are more likely to be affected by it than groundwater. They are significantly affected by changes in rainfall (Pavelic et al. 2013). With most areas of Africa expected to face decreases in precipitation, this decrease will be passed onto surface water supplies, particularly run-off (Ziervogel et al. 2010). Streamflow projections show they are likely to decrease under climate change – river runoff faces declines of 10-30% in the dry tropics and most conclusions have them set to decrease more generally overall in Africa (Kusangaya et al. 2013). The magnitude of this decrease is uncertain. Additionally, evaporative increases, due to temperature increases, could reduce outflows from reservoirs (Kusangaya et al. 2013). When faced with drought or prolonged dryness, surface water supplies are prone to fail and can prove insufficient (Calow and MacDonald 2009). Changes is surface water supply have proved rather destructive in the past, leaving people without access to water, and consequently food (deWit and Stankiewicz 2006). The vulnerability of surface water to climatic changes means they are not a suitable resource to rely upon in the uncertain face of global climate change.

A well dug in Kunjuru - the prolonged drought has meant that the river has dried up

Source: UN Multimedia

Deep groundwater stores generally prove to be more resilient to changes in rainfall - its “buffering capacity” makes it a more consistent source of water for irrigation in a region facing increasingly variable precipitation (Calow and MacDonald 2009: 1, Conway et al. 2008). Sub-surface aquifers' water storage capacity is often greater than their yearly recharge, meaning they are able to continue to supply water even when rainfall supply is low for an extended period (Calow and MacDonald 2009). Groundwater recharge can be stored for several decades (MacDonald et al. 2012). During periods of prolonged drought, deep groundwater supplies prove more reliable than their shallow counterparts and surface supplies (Calow and MacDonald 2009). Climate change will also likely result in an intensification of precipitation, which will benefit groundwater recharge. The relationship between rainfall and recharge is non-linear, meaning that extreme rainfall is required to generate significant groundwater storage, which is required for agricultural uses (Taylor et al. 2013, Calow and MacDonald 2009).

Groundwater stores are not immune to the effects of climate change. However, it does appear to be a better insulated water supply, therefore proving more reliable water supply for agricultural needs (Kusangaya et al. 2013).