Sunday, October 7, 2012

Monthly Blue Water Scarcity Indicator

The world population growing at rapid pace and related changes in lifestyle as well as consumption patterns, competition for water resources between sectors such as agriculture, industry and energy, sustaining ecosystem health, are merely a few among several pressing issues that are inseparably connected with water scarcity. The rising water demands require governance based on accurate and reliable indicators. The research group of Arjen Hoekstra of University of Twente, in collaboration with the Water Footprint Network and its partners WWF-World Wide Fund for Nature and The Nature Conservancy, developed an innovative water scarcity indicator, that combines three improvements compared to previous indicators: (i) use of water consumption of ground- and surface water flows (i.e. the blue water footprint) instead of water withdrawal, (ii) accounting for environmental flow requirements to sustain critical ecological functions and (iii) a monthly rather than an annual time-step. Blue water scarcity is defined as the ratio of blue water footprint to blue water availability, whereby the latter is determined by subtracting the presumed environmental flow requirement from the natural runoff.
Water scarcity has been analyzed for the time period 1996-2005 and categorized from low to severe for 405 river basins that account for 69% of global runoff, 75% of the world’s irrigated area, and 65% of world population. Improving upon previous assessments, the current monthly approach reflects the dynamic character of the hydrologic cycle and the variability of human water use over the course of a year. For the assessment of social, economic and environmental impacts of water scarcity both severity and duration of water scarcity are crucial (see the accompanying Figure from Hoekstra et al., 2012). One result of the study was that in 223 river basins (55% of the basins studied) the blue water footprint exceeds blue water availability during at least one month of the year, impacting 2.72 billion people, i.e. 69% of the population considered. For 201 of these basins, with in total 2.67 billion inhabitants, there was severe water scarcity during at least one month of the year, highlighting the fact that when water scarcity exists it is usually of a severe nature. This innovative water scarcity indicator may prove useful for governments, businesses, farmers, investors and others to evaluate water-related risks.
The data on blue water scarcity are available from the WaterStat database of the Water Footprint Network (

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