Iran is in the grip of a seven-year drought that shows no sign of breaking and that, many experts believe, may be the new normal. Even a return to past rainfall levels might not be enough to head off a nationwide water crisis, since the country has already consumed 70 percent of its groundwater supplies over the past 50 years.

Always arid, Iran is facing desertification as lakes and rivers dry up and once-fertile plains become barren. According to the United Nations, Iran is home to four of the 10 most polluted cities in the world, with dust and desertification among the leading causes.

In Zanjan, northwest of Tehran, the historic Mir Baha-eddin Bridge crosses a riverbed of sand, stones and weeds. In Gomishan, on the shores of the Caspian Sea, the fishermen who once built houses on poles surrounded by freshwater now have to drive for miles to reach the receding shoreline. In Urmia, close to the Turkish border, residents have held protests to demand that the government return water to a once-huge lake that is now the source only of dust storms.

More than 15 percent of the approximately 150,000 acres of pistachio trees in the main producing area in Kerman Province have died in the last decade or so.