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The Metric

Jan 17, 2014

Evolution of water quality indicators in the EPI

Image Credit: Otmar Winterleitner/Hemera/Thinkstock

Over the past 15 years of the EPI (and its predecessor, the Environmental Sustainability Index), we have seen improved data and indicators in a number of areas, including biodiversity conservation, oceans and fisheries, and climate change. Data challenges, however, have persisted in some key areas such as water quality, water scarcity, and water management. The gap is especially glaring since improvements in water quality are generally seen as a major benchmark of environmental performance, and water resources management is a critical factor in sustainable development. Scalable1 indicators that describe the management of water resources and the status of aquatic ecosystems – and that can guide government efforts in water resources management – are certainly in demand.

Over the years, the EPI has sought to measure country-level water quality in a number of ways using at different times in situ monitoring data and modeled data (including data from hydrological models). Early versions of the Environmental Sustainability Index relied on modeled data of biochemical oxygen demand from the World Bank, and crude estimates of national water availability from the UN Food and Agriculture Organization’s Aquastat. Later versions of the Environmental Sustainability Index attempted to aggregate data from the United Nations Environment Programme Global Environment Monitoring System (GEMS)/Water Programme database, GEMStat, with limited success. In 2006, modeled nitrogen loads were used to calculate nitrogen concentrations by river basin. From 2008 to 2010 the EPI team partnered directly with GEMS/Water to produce a Water Quality Index based on in situ monitoring data for dissolved oxygen, conductivity, pH, nitrogen, and phosphorus, but this effort was eventually abandoned owing to data gaps.2

For the 2012 EPI, indicators of water quality were discarded in favor of a measure of alterations in natural river flow caused by water withdrawals and reservoir construction (based on modeled data from Doll et al. 2009),3 but this was a crude proxy at best and suffered from the lack of regularly updated data. The EPI has also experimented with a number of water stress indicators, mostly based on calculations derived from global hydrological models. Examples include percent of territory under water stress (where withdrawals are greater than 40 percent of supply), and a measure of scarcity that allowed arid countries to compensate for limited natural endowments with desalination and treated wastewater.

Collectively, these indicators are not capturing the most policy-relevant issues, and in many cases are too heavily influenced by each country’s water endowment. Conversations with other groups seeking to develop country-level water indicators suggest that these challenges are widely shared. Therefore, the 2014 EPI includes a new indicator of national wastewater treatment. Designed and compiled by the Yale Center for Environmental Law & Policy, this new indicator is a first step toward developing more performance-relevant measures of ecosystem water quality.

1 A scalable indicator can be developed for any level of jurisdiction, from district/county up to country level.

2 Srebotnjak, T., Carr, G., de Sherbinin, A., et al. (2012) A global water quality index and hot-deck imputation of missing data. Ecological Indicators 17:108-119.

3 Döll, P., Fiedler, K., and Zhang, J. (2009) Global-scale analysis of river flow alterations due to water withdrawals and reservoirs. Hydrology and Earth Systems Science 13:2413-2432.