Blog | August 3, 2016By Peter Gleick, President Emeritus and Chief Scientist Much more can and should be done with new data and methods to improve our understanding of water challenges, says Peter Gleick.
As populations and economies continue to expand and as anthropogenic climate change accelerates, pressures on regional freshwater resources are also growing. A wide range of assessments of water pressures has been produced in recent years, including the regular updates from the United Nations World Water Development Reports (WWAP 2003, 2006, 2009, 2012, 2014, 2015), the biennial assessment The World’s Water (Gleick et al 1998–2015), the Aqueduct water stress datasets produced by the World Resources Institute (WRI 2015), and numerous other efforts to develop quantitative water measures and indices. The development of such methods has become increasingly common in recent years in order to help measure progress and evaluate the impacts or effectiveness of water policies and practices. The new letter in this volume of Environmental Research Letters by Padowski et al (2015) offers another opportunity to evaluate freshwater threats and vulnerabilities. There are several challenges associated with any effort to produce metrics to evaluate water-related vulnerabilities. These include the definition of ‘vulnerability’ or ‘risk,’ the selection of indicators across a range of scientific, hydrologic, economic, social, and political variables, the quality and availability of data, and the strategy used to weight, prioritize, or combine different measures into indices. A distinction must be made between different kinds of data and measures. Typically, the term ‘indicator’ or ‘measure’ refers to a single number derived from a variable that can be measured at a single place or time, or over a period of time, to denote the direction and magnitude of change. An ‘index’ is typically a single number that is a mathematical aggregation of two or more indicators (Gleick et al 2002). The Padowski et al letter acknowledges the challenges of producing such metrics and attempts to address them by defining four separate categories of vulnerability (‘demand, endowment, infrastructure, and institutions’), identifying specific measures for each category, and (to their credit) by reporting on them separately and resisting the temptation to combine them into a single index. This effort builds on previous efforts to develop indices of vulnerability, including the Stockholm environment institute water resources vulnerability index in 1997 (Raskin 1997), the index of relative water scarcity (IRWS) developed by IWMI in the late 1990s (Seckler et al 1998), the water poverty index (Sullivan et al 2003), and work by many others (e.g., Gleick et al 2002, Garriga and Foguet 2010, Plummer et al 2012). All together, they identify 19 indicators: six related to water demand, six to water endowments, two to infrastructure, and five to institutions. The data are developed at the country level, rather than the watershed level. Of the 19, 15 are considered ‘endogenous’ to the countries evaluated. The remaining four are exogenous, measuring food calories imported, water quantity and pollution that originates outside of a country’s borders, and virtual water imported in goods and services consumed internally. The biggest challenge in developing vulnerability assessments has always been data limitations and quality. Such assessments are not limited by computer capability or the ability to conceive of or identify key components or factors that affect water risks. Instead they are limited by:
- Gaps in data on water availability, including basic hydrologic data such as groundwater availability, runoff, and evapotranspiration for watersheds and countries.
- Changes in definitions or methods of data collection over time, such as the definitions of ‘access’, ‘clean water’, and ‘sanitation services’ used by the United Nations.
- Very inconsistent collection and definition of water-use data across regions, watersheds, and economic sectors.
- Restrictions on access to water data in some regions.
- The inability to quantify some kinds of water metrics, such as ecological water needs or recreational uses, and especially institutional variables such as governance, regulatory effectiveness, or management ability.
- Uncertainties about how climatic changes are already altering water supply, demand, quality, and other variables, and will continue to do so in coming decades.