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.
