Water scarcity is defined as the gap between the available supply and the expressed demand of freshwater in a specified domain, under prevailing institutional arrangements (including both resource ‘pricing’ and retail charging arrangements) and infrastructural conditions (FAO, 2012 forthcoming).
Introduction
Water scarcity = an excess of water demand over available supply
Scarcity is signaled by unsatisfied demand, tensions between users, competition for water, over- extraction of groundwater and insufficient flows to the natural environment.
Water scarcity is caused by a wide-ranging combination of factors, all which are related to human interference with the water cycle. Water scarcity is fundamentally dynamic: its level can vary within a given time frame as a result of natural hydrological variability, but even more so due to prevailing economic policy, planning and management approaches, and the varying capacity of societies to anticipate changing levels of supply or demand. Scarcity can result from short-sighted policies, such as the over-allocation of water use licenses in a river basin, or from the excessive expansion of irrigation areas with free or low-cost water for farmers. The problem intensifies with increasing demand by users and/or with the decreasing availability and quality of the resource. Scarcity can arises in close juxtaposition with water plenty if there is no legal or institutional arrangement in place to improve access, or if the required infrastructure does not exist or is not feasible. When identified correctly, many causes of scarcity can be predicted, avoided and/or mitigated.
Related terms
Water shortage: a shortage of water supply of an acceptable quality; low levels of water supply at a given place and a given time relative to design supply levels as a result of insufficient water resources, lack of infrastructure or poorly maintained infrastructure; low levels of water resources as a result of annual or seasonal differences in climate or a range of hydrological or hydro-geological factors. Water shortage is an absolute, not a relative, concept.
Water stress: the symptoms of water scarcity or shortage: e.g. growing conflict between users and competition for water, declining standards of reliability and service, harvest failures and food insecurity.
Dimensions of water scarcity
The causes of scarcity, as indicated in the chosen definition, may be of a varying nature, with each requiring a specific response. FAO proposes three main dimensions of water scarcity that can be summarized as follows:
(i) scarcity in availability of water of acceptable quality with respect to aggregated demand, in the simple case of physical water shortage;
(ii) scarcity due to the lack of adequate infrastructure, irrespective of the level of water resources, because of financial , technical or other constraints; and
(iii) scarcity in access to water services because of the failure of institutions (including legal rights) in place to ensure reliable, secure and equitable supply of water to users. This dimension relates to the organizational and accountability dimensions proposed by the World Bank (2007).
Indicators of water scarcity
The best-known indicator of national water scarcity is per capita renewable water, with threshold values of 500, 1.000 and 1.700 m³/person/year used to distinguish between different levels of water stress (Falkenmark and Widstrand, 1992, UN-Water, 2006b). Following this criterion, countries or regions are considered to be facing absolute water scarcity if renewable water resources are < 500 m³ per capita; chronic water shortage if renewable water resources are between 500 and 1000 m³ per capita; and regular water stress between 1.000 and 1.700 m³ per capita (Table 1). This crude approach to measuring water scarcity is primarily based on estimates of the number of people who can live reasonably with a certain unit of water resources (Falkenmark, 1984). This indicator is widely used as it can be easily calculated for every year and every country in the world, based on water resources data (FAO-AQUASTAT, 2012) and available population data (UN, 2009). Furthermore, population projections, available until 2100, allow for projections of water scarcity levels in the forthcoming decades.
Table 1: Conventional definitions of levels of water stress (after Falkenmark and Widstrand, 1992)
| Annual renewable freshwater (m³/pers.yr)
|
Level of water stress
|
| < 500
|
Absolute water scarcity
|
| 500 – 1.000
|
Chronic water shortage
|
| 1.000 – 1.700
|
Regular water stress
|
| > 1.700
|
Occasional or local water stress
|
In arid and semi-arid regions, water is an even more essential factor for agriculture and food production. IPCC assessments predict (IPCC, 2007) that in most of these regions climate change will further acerbate the water scarcity due to changed rainfall patterns and/or reduced rainfall. It is estimated that 14 % more freshwater will have to be withdrawn for agricultural use in the next 30 years (UN, 2006). This underscores how urgent the need is for a more efficient and productive water use.
Links
http://www.un.org/waterforlifedecade/scarcity.shtml
http://www.unep.org/dewa/vitalwater/jpg/0221-waterstress-EN.jpg
http://www.ipcc.ch/publications_and_data/ar4/syr/en/spms3.html
http://www.ipcc.ch/publications_and_data/ar4/syr/en/spms3.html
Literature
Falkenmark, M & Widstrand, C. 1992. Population and Water Resources: A delicate balance, Population 41 Bulletin, Washington: Population Reference Bureau.
Falkenmark, M. 1984. New ecological approach to the water cycle: ticket to the future. AMBIO 13(3)
FAO, 2012: Water scarcity and food security. A framework for action. To be published.
FAO-AQUASTAT. 2009. FAO Global information system on water and agriculture. 16 http://www.fao.org/nr/water/aquastat/maps/index.stm
United Nations (UN). 2009. United Nations Population Information network online database. 4 http://www.un.org/popin/ (cited November 2009).
UN-Water. 2006b. Coping with water scarcity: A strategic issue and priority for system-wide action. 11 http://waterwiki.net/images/9/92/UN_Water_-_waterscarcity_leaflet.pdf.
World Bank. 2007. Making the Most of Scarcity: Accountability for Better Water Management Results in the Middle East and North Africa. Washington, USA
