Water scarcity compares water demand (or water withdrawal) and water availability to estimate the amount of water left over when all demands are fulfilled using the available water. It is normally expressed as a ratio (water withdrawal / water availability) and environments with a ratio of 0.4 or more are considered to be in a state of severe water scarcity. Beekman et al. (2009) suggest that water scarcity is an essential cross-cutting vulnerability issue that should be considered in all development initiatives.
Increasing water scarcity across the globe.
Source: World Water Assessment Programme, 2009; adapted from Comprehensive Assessment of Water Management in Agriculture 2007
( click to enlarge )
Water scarcity can be portrayed as physical water scarcity, where the limiting factor is an actual physical lack of water due to climatic or other environmental conditions; or economic water scarcity, where there is water, but economic factors influence access to clean or potable water. This can be seen in the following map from the recent United Nations World Water Development Report 3 (World Water Assessment Programme 2009).
Determining Water Shortage and Water Scarcity
There are a number of problems related to determining water shortage and water scarcity. In general, national average figures are used which mask annual variability from year to year, seasonal variability and the regional variability within countries.
The Food and Agriculture Organisation (FAO) of the United Nations regards water as a severe constraint on socio-economic development and environmental protection at levels of internal renewable water availability of less than 1 000 m³/capita. At levels of water availability of less than 2 000 m³/capita, water is regarded as a potentially serious constraint, and a major problem in drought years. Water scarcity provides a measure of the sensitivity of a given situation to drought. In situations where the average availability of water per capita is low, even slight variations can render whole communities unable to cope and create disaster conditions.
Water scarcity is a relative concept – it is partly a "social construct" in that it is determined both by the availability of water and by consumption patterns. Because of the large number of factors which influence both availability and consumption, the determining of water scarcity will vary widely from country to country and from region to region within a country. Adopting a global figure to indicate water scarcity should therefore be done with great caution. Whilst a threshold such as 1000 m³/capita may be useful for purposes of comparison, it should be carefully used because it may understate situations of potentially serious water stress.
Because the concept of water scarcity is a social construct or, put in other terms, a matter of political and economic perception, it may be more useful to describe water scarcity as a particular mix of availability and demand at which water stress occurs, rather than a per capita figure. This means that its determination is more qualitative than quantitative, as the point at which water scarcity occurs may vary widely from one situation to another. In a semi-arid highly industrialised country or in a country where food security is dependent upon the extensive use of irrigation, the aggregated per capita figure at which water becomes sufficiently scarce to cause internal or transboundary conflict may be a lot higher than in a temperate, less highly developed country.
Source: The Water Page, http://www.africanwater.org/drought_water_scarcity.htm
In a region such as the Kunene River basin, where groundwater has an important role to play for human water supply, Groundwater Recharge is key to water availability and water scarcity. Groundwater recharge is defined as the amount of water that is added to the groundwater table. Recharge is normally considered in terms of the amount of water falling as precipitation that reaches an aquifer, however it also includes water entering from an adjacent aquifer, from surface water sources or injection of water into an aquifer (artificial recharge) (Beekman and Xu 2003).
