Isfahan is the third-largest city in Iran, renowned for its UNESCO World Heritage listed central square, the Shah Mosque, and several ornate bridges crossing the Zayandeh River. At least the bridges used to cross the river. Since 2011, following years of seasonal dry-outs, the Zayandeh River has run dry before it reaches the city. About 80% of the water in its upper reaches is used for irrigation, and the remainder is abstracted for human consumption and industry. The resulting dry riverbed isn’t just an inconvenience and an eyesore for residents and tourists, it serves as a symbol for the water insecurity faced by Iran and other Middle Eastern countries. See Box 1.
Water insecurity is caused by either water stress (when demand for water exceeds the available amount during a certain period or when poor quality restricts its use) or the more long-term state of water scarcity (when demand for water exceeds its supply). These are sometimes differentiated by the volume of water available per capita per year: 1,000 m3 to 1,700 m3 for water stress, and 500 m3 to 1,000 m3 for water scarcity. Water scarcity can involve physical scarcity (insufficient water to meet demand) and/or economic scarcity (people can’t afford water, even if it is available).
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