State indicators

Natural availability

The amount of water available in a region depends on total rainfall, its seasonal distribution, seasonal temperature and solar radiation patterns and the regional topography. Renewable or naturally available water includes mean surface runoff and mean aquifer recharge. The natural availability of water is frequently expressed in terms of size of the population living in a given area. Regions where less than 1 700 thousand cubic meters of water are available per capita per year are considered to be under "water stress", and water shortages may occur frequently. When availability is lower than one thousand cubic meters per capita per year, consequences may be more severe and lead to problems in food production and economic development, unless the region can invest in new technologies for water use, conservation and reuse. The indicator Mean natural availability per capita shows the mean annual volume of renewable water per capita (UN, 2003b) and is one of the indicators proposed by the World Bank (WB, 2009) and the United Nations (UN, 2007).

 Water use intensity

A frequently used indicator of water use intensity is the Water stress, which describes the relationship between total extraction and availability of renewable water resources in the area. It is used as a measure of the country's vulnerability to water shortages (UN, 2007). When the degree of pressure is higher than 40 percent, the region is considered to be under severe water stress, which could lead to strong competition for water. Equivalent indicators are used internationally by the UN, the OECD and EEA (UN, 2007; OECD, 2008; EEA, 2009a).

Importantly, the indicator Water stress does not directly consider the environmental water requirements, defined as the quantity and quality of water required for aquatic ecosystems in order to protect and maintain their structure and functioning (Smakhtin et al., 2003). Excessive water extraction without considering aquatic ecosystems results in: reduced river flows and volume in lakes¹, alteration or disappearance of aquatic habitats, reduction of biodiversity that depends on them, fisheries collapse, and species extinction (Hinrichsen, 2003).

Overexploited aquifers and aquifers with salinization problems

The extraction of a significant portion of groundwater resources might lead to regional decreases in groundwater levels, dry wells, higher extraction costs due to the increased depth to the water table, land subsidence, saline intrusion and reduced water flow in freshwater ecosystems (Stromberg et al., 1996; Zektser and Everett, 2004; EEA, 2009b). Furthermore, in arid zones, closed basins and coastal areas with naturally saline soils, poor irrigation management can cause groundwater quality issues. The indicator Overexploited aquifers, aquifers with seawater intrusion and/or soil salinization or brackish groundwater problems aims to show the magnitude of this issue through the number of cases of mismanagement that have led to aquifer overexploitation; indirectly, this indicator provides information on water supply risk.

¹ This reduces the ability of water bodies to purify circulating water.