The relationship between water and people necessitates measuring freshwater availability or “water scarcity”. Water scarcity can be defined as “a shortage in the availability of freshwater relative to demand” (Taylor 2009).
This post explores how the water crisis and its scarcity has been measured in Africa. I will examine two metrics: Falkenmark’s (1989) Water Stress Index (WSI) and Sullivan’s (2002) Water Poverty Index (WPI). I aim to explain how these metrics may be deemed at best inadequate at assessing water scarcity in Africa and at worst, misrepresents the entire scenario.
Falkenmark’s (1989) Water Stress Index
Falkenmark’s (1989) WSI is one of the first quantitative metrics to assessing water scarcity. The metric was conceived during the Sudano-Sahel famine of Africa as a means of informing methods for food security while taking into account freshwater availability, a growing population and by extension a demand for water and food in Africa.
The WSI sets the threshold for water scarcity at 1000 persons/flow unit (Falkenmark 1989). Each flow unit of water = 106 m^3/year. Putting those two together, water scarcity exists if each person has access to less than 1000 m^3 of renewable (annual) freshwater resources.
Advantages of WSI
The threshold = 1700 m^3/capita/year is easy to use. It either is or is not.
The calculation of the WSI uses the mean annual river runoff (MARR) which is relatively easily accessible and makes calculation easy.
Limitations of WSI
Precisely because the MARR is used for the calculation, it masks changes in soil moisture and groundwater storage – sources that are equally crucial in measuring freshwater availability (Taylor 2009) and variabilities which (trickily) are substantial in sub-regions like sub-Saharan Africa (McMahon et al 2007)
It does not take into account soil water (i.e. “green water”) which is an important water in the agriculture sector. The latter accounting for accounts for a whopping 70% of global water use.
Technical challenge of including freshwater stores. Current hydrological models are still unable to integrate time-variant inputs/outputs to freshwater stores at a national scale globally. There however have been improvements such as the GRACE project that uses twin satellites to monitor changes in groundwater storage.
More “Holistic” Measures
The desire to conceive more holistic measures is perhaps the result of acknowledging that the physical and the human sciences cannot be neatly separated. Holistic measures take into account the human ecology of it – assessing the interactions between human and the environment, seeking to incorporate knowledge from both the physical and human sciences.
Sullivan’s (2002) Water Poverty Index
An example of a holistic measure is the Water Poverty Index (WPI). Beyond availability of water in volumetric terms, it takes into account five (weighted) components:
Available water resources (via WSI)
Access to water
Capacity for water management
Water uses for domestic food and production purposes
Environmental concerns
Advantages
Acknowledges how the physical and human are intertwined
Limitations
Quantifying the social is inherently difficult. Subjectivity is concealed in the design of such a metric – what do you include, what do you exclude.
Results are highly local in nature. This would make comparative analysis between geographies difficult (Garriga and Foguet 2010). An extension, the same variable that wish to be tested may be not be translatable in different say rural/urban settings.
The same limitations that WSI had measuring availability of water resources persists.
It may be more suited as a means of politicising the water debate than be used for an actual of measurement of water scarcity (Lawrence et al 2002).
Conclusion and Why it Matters
Having gone through that little crash course on how water scarcity is measured, the question you may be having now is “okay... so what?”.
Firstly, how water scarcity is measured and defined will give us different questions, problems and answers. The nuance between water stress and water scarcity already counts for one source of confusion for the average reader. Different benchmarks will give rise to different problems and a different accompanying set of solutions.
Second, indeed so what – so what if we have measured water scarcity when water scarcity ≠ access to safe water. There is no statistically significant relationship between the availability of freshwater and access to safe water (Damkjaer and Taylor 2017, and supported by Chenoweth 2008). This is especially so when the 1700 m^3/capita/year threshold includes water for industrial and agricultural use and does not contribute directly to human consumption.
Lastly and perhaps the most relevant for a blog dedicated to understanding food and water in Africa is that even with quantitative and qualitative metrics, the simple fact is that we still need a metric that accounts for renewable resources (e.g. green water), climate change and distribution of overall resources. This is particular the case when the climatic conditions are highly varied across the African continent – a situation exacerbated by climate change. By corollary, this has impacts on groundwater resources and its corresponding opportunities and challenges for food and water in Africa.
In the next blog post, we take a closer look at the physical landscape of Africa and its groundwater potential for agriculture.