Measuring water scarcity: Evolution of Metrics

It often comes to our mind that water is seen as a scarce resource in Africa, but how do we actually measure it? It is definite in saying that water plays an essential role in food security and supporting the basic needs of human beings. There is an unbreakable link between water and food production in creating a sustainable agricultural system (Vilakazi et al, 2019). In this blog, I will talk about the water scarcity metrics, and link the issue of water scarcity together with food security in Africa. 

Water Stress Index (WSI)

Falkenmark came up with the concept of the Water Stress Index in the early 1980s linking freshwater availability and food security. The WSI was created to serve as a warning system for new measures to deal with the expanding population in the Sudano-Sahel region of Africa, which is now experiencing famine (Taylor, 2017). Since then, WSI has been the most commonly used metric in measuring water scarcity. A country is considered as being scarce in water if the renewable water supply is below 1000 cubic metres per capita per year based on the ‘hydraulic density of population’ (Falkenmark et al., 1989). 

Since then, the use of WSI has been encouraged as a method of equating renewable freshwater resources to mean annual river runoff (MARR) (Taylor, 2017). As a result, concealing freshwater resources’ inter- and intra-annual variations has increased its difficulty (Taylor, 2009), where this variability is extreme in Sub-Saharan Africa (McMahon et al, 2007). Furthermore, MARR ignores soil water (green water) in its calculation, which is an essential part of determining the demand for agricultural water (MacDonald et al. 2012; Rockstrom and Falkenmark,2015).

Adding on to WSI, the withdrawal-to-availability ratio (WTA) defines water scarcity by calculating the ratio of annual withdrawals in the domestic, industrial and agricultural sectors compared to the annual resources estimated through using MARR (Raskin et al., 1996). WTA identifies water scarcity if this ratio exceeds 40%. WTA, like WSI, obscures freshwater’s supplies with the seasonal and inter-annual variability (Taylor, 2009).

Map of physical and economic water scarcity in Africa (2007) - Source

The emergence of more holistic metrics

As time passes, more metrics are being used in measuring water scarcity that characterised the adaptive capacity and introduced the concept of environmental water demand (Taylor, 2007).

For example, Ohlsson explicitly considered ‘adaptive capacity’ in the Social Water Stress Index (SWSI), where it included the use of the Human Development Index (HDI) as a proxy for the adaptive capacity to water shortages in a country. The SWSI provides for a comparison of WSI and SWSI in terms of a country's adaptive capacity. Through using the SWSI, countries' status of water scarcity can be changed. In Ohlsson’s analysis in 2000, countries such as South Korea and Poland where they were identified as water-stressed using the WSI changed to being ‘relatively sufficient’ because of their high HDI value, meaning that they have high adaptive capacity. However, countries in Africa such as Niger, Nigeria and Burkina Faso moved from ‘relatively sufficient’ to ‘water stress’ with their low HDI scores.

However, the use of HDI does not reveal anything beyond the economic factors and could simplify and misrepresent countries (Ogwang, 1994). But it is true that some countries in Africa do suffer more from water scarcity because of their low adaptive capacity.

Water scarcity and food

Water scarcity is receiving more attention as we start to realise its role in a country’s socio-economic development. The UN has also set specific goals in the SDGs that ensure access to water and sanitation for all (United Nations, 2015). The problem of water scarcity is more prominent in less developed countries, which makes Africa being more important and relevant to this topic of reaching this goal. Although progress is being made in global food security in recent times, it still remains a big challenge in Africa (Senker, 2011). The internal variability and irregular distribution of rainfall and the low adaptive capacity of Africa make it even harder for Africa to escape from food insecurity. 

 

In my next blog post, I will dig into the issue of water scarcity and quality and its relationship with food security. Stay tuned!