Climate change and groundwater-a plausible solution?

Following from last week’s post on the projected effects of climate and demographic changes on water resources in Africa, my post this week dwells a little deeper into the effects of climate change on groundwater in Sub-Saharan Africa (SSA), based on an article by Taylor et al. (2009): ‘Groundwaterand climate in Africa-a review’.

The paper provides a broad overview of the predicted relationships between climate change and groundwater resources, based on whatever limited data that is available on this area. For example, due to the lack of long-term studies of recharge in Africa, it is difficult to balance a highly variable episodic recharge with groundwater withdrawals over decadal, rather than annual time scales.

The potential of groundwater as a viable source of water, in the absence of surface water was nonetheless argued for in the paper:

• Groundwater may be the only source of freshwater present if surface waters are not available. 
• Groundwater is often of potable quality and does not need expensive treatment.
• Due to the slow rate of groundwater movement, and the storage of aquifers, groundwater resources may be more resilient to climate variations than surface water resources

Furthermore, empirical evidence from studies including that by Taylor and Howard (2006) showed a strong correlation between the sum of heavy rainfall events exceeding a threshold of 10mm/d and recharge flux, which is in line with the prediction that as warming continues, and the moisture-holding capacity of the atmosphere increases (defined by the Clausius-Claperyon relationship), so will the frequency of heavy rainfall events, especially in the tropics, where air temperatures are higher, contributing to groundwater recharge.

Given that small-scale farming accounts for 70% of agricultural production in SSA, the benefits of increased groundwater recharge with climate change could manifest in groundwater abstraction from discrete low-yielding aquifers in weathered crystalline rock and mudstones that underlie more than 50% of SSA may be suitable as they are self-regulating, which prevents impacts of local overdevelopment and solving the age-old problem of allocation. Low-intensity groundwater abstraction in parts of SSA has been featured as an example of the utilisation of groundwater in small-scale farming, and possibly for domestic uses.

But the sustainability of adaptation strategies employing groundwater to alleviate water scarcity brought about by increased demand or climate change is unclear. Contamination of shallow groundwater supplies, due to inadequate community hygiene in many rapidly-urbanising centres, is also of great concern.

My thoughts and reflections on the paper:

While groundwater does hold promise as a viable alternative to surface water as rainfall patterns become increasingly erratic with climate change, harnessing it effectively, in suitable and needy parts of SSA remains a long shot. As mentioned in the paper and the summary, the non-renewability of groundwater may mean that supplies could be depleted if the scale and intensity of abstraction is increased.

Moreover, the uncertainty of predictions of the effects of climate change on recharge, propagated through the use of projected parameters like rainfall and evapotranspiration and then the conversion of monthly to daily rainfall, means that the cause-effect relationship between intensification of rainfall patterns and groundwater recharge is still rather tenuous and awaits further investigation through applied, interdisciplinary research in this area.

It was also clear that active harnessing of groundwater, possibly for agriculture on larger farms, beyond that for subsistence has to be accompanied with improvements in other areas, such as the provision of sanitation to prevent contamination of shallow groundwater with faecal matter and transboundary agreements for the equitable use of groundwater, given that at least 40 transboundary aquifer systems have been identified thus far.

The paper refers to the use of ‘plausible projections of possible future’ rather than climate projections which I will read up on and seek to find out why the former might be preferred over the latter.

More to come in the coming weeks...

References: 

Taylor, R. G. and K. W. F. Howard (1996) 'Groundwater recharge in the Victoria Nile basin of East Africa: support for the soil-moisture balance method using stable isotope and flow modelling studies, Hydrological Journal, 180, 31–53.

Taylor. R.G., A.D. Koussis and C. Tindimugaya (2009) 'Groundwater and climate in Africa—a review', Hydrological Sciences–Journal–des Sciences Hydrologiques, 5,4, 655-664.