Adapting to Climate Change: Groundwater

Climate change largely influences surface water sources through altered rainfall patterns, evaporation rates and changing temperatures, whereas groundwater resources are more resilient to climate change and thus offers a reliable supply of water (Calow et al., 2010). Groundwater resources can provide an important buffer to climate change because despite aquifers being highly unevenly distributed across Africa, the smallest or poorest aquifers can still contain enough water for pumping to local communities during dry rainfall seasons or long periods of drought (MacDonald, 2012). In this blog, I would like to explore how groundwater resources respond to climate change and thus the role of groundwater resources as an adaptive measure.

Groundwater resources typically store a certain amount of water depending on the geology, geomorphology, and effective rainfall of the aquifer, which in turn influences the transmissivity, porosity, saturated thickness, and recharge rates of the aquifer (MacDonald et al., 2012). The largest aquifers in the African continent lies in the northern region, where countries like Libya, Algeria, and Egypt have the largest reserves of groundwater (Figure 1). Aquifers with lower storage capacities varies across the continent due to different rock formations; the lowest groundwater storages are underlain by Precambrian basement rocks (MacDonald et al., 2012). However, despite some areas having large or small storage capacities, the yield of the aquifer and borehole limit the productivity of these aquifers. The yield of a borehole or hand pump to the aquifer will limit how much water can be abstracted and used, therefore even though some countries have large aquifers, the productivity of these aquifers may be low where little water can be abstracted and used. Figure 2 shows the productivity of aquifers, and comparing this to figure 1 for example, shows that the aquifer underlying the South Sudan region has a relatively high groundwater storage of 25,000-50,000 mm, however it has a moderate productivity level of 1/5 ls^-1. 

Figure 1. Groundwater Storage (MacDonald et al., 2012)                         Figure 2. Aquifer Productivity (MacDonald et al., 2012)

Climate change rarely impacts the geology and geomorphology of groundwater resources; however, climate change directly influences groundwater resources through groundwater recharge processes (Taylor et al., 2012). The replenishment of groundwater resources relies upon recharge from either rainfall or the leakage from surface water resources. The IPCC’s fifth assessment report predicts that rainfall patterns are likely to become more highly variable, both spatially and temporally where droughts and intense rainfall periods are likely to occur (IPCC, 2014), and this in turn will likely influence groundwater recharge.

A study by Owor et al. (2009) attempted to determine a relationship between groundwater recharge and climate change using a rare set of data, which consists of daily rainfall and groundwater levels in the Upper Nile Basin of Uganda. The study related the magnitude of recharge events to the sum of daily and annual sum of daily rainfall exceeding a threshold of 10mm^-1, and they have found that groundwater recharge is better related to heavy rainfall periods, exceeding a threshold of 10mm^-1, compared to daily rainfall rates. Their conclusion of this analysis suggested that climate change may indeed have a positive influence on groundwater recharge because the predicted increased frequency in rainfall intensity can promote increases in groundwater recharge instead of restricting it. Similarly, another study by Mileham et al. (2009) found that groundwater recharge was higher when intense rainfall was accounted for when modelling the influence of climate change projections on groundwater recharge. A mean monthly delta factor of climate change was applied to the SMBM while using a historical rainfall distribution (period 1960-1990), groundwater recharge is projected to decrease by 55%, whereas runoff is predicted to increase by 86%. However, when this historical rainfall distribution is adjusted to account for the projected increase in intense rainfall patterns for a future period (2070-2100), groundwater recharge and runoff is predicted to increase by 53% and 137% respectively. Hence, this also shows that groundwater recharge is positively influenced by intense rainfall, and the distribution of daily rainfall is also an important factor when modelling groundwater recharge.

These studies have shown that the projected intense rainfall will likely improve groundwater recharge and thus the amount of groundwater stored. This in turn can prove to be a reliable source of freshwater, especially during periods of drought. An article by Oliver Balch (2016) agrees that the increased use of Africa’s aquifers can help to reduce water stress and insecurity. Initiatives by the International Water Management Institute and the Groundwater Solutions Initiative for Policy and Practice aims to enhance the use of groundwater resources for agricultural and domestic needs, to reach the UN Sustainable Development Goals in reducing water scarcity. However, the article stresses the importance of overexploitation and sustainable consumption of groundwater, noting that the Saiss aquifer water table has fallen by an annual average of 3meters over the past 20 years (Balch, 2016). It is important to recognise that despite groundwater being a reliable source and adaptive strategy to climate change, it is important that groundwater use is sustainable. A study by Knuppe (2011) conducted interviews with management experts in South Africa to determine the key challenges in the sustainable use and management of groundwater resources. Climate change will have uncertain consequences on groundwater resources but the stress and exploitation on this resource will increase due to the undervaluation of groundwater, the need for information at all levels in a community, the centralisation of power, governance and management, and the disregard for ecosystems and its services. A water planning expert, Callist Tindimugaya in the Balch article says that groundwater resources are an “invisible commons” because there is a lack of information amongst the people using this resource, and thus they do not comprehend how to use this resource sustainably. A lack of central planning and policies leads to inefficiencies, and ultimately poor management resulting in intensive and exploitative use of groundwater. Therefore, it is also important to consider the combination of socio-economic and physical context of using groundwater resources, especially when using groundwater as an adaptive strategy to climate change.