Why is Tehran running out of water?
This is the original story It appeared in the Bulletin of the Atomic Scientists and is part of the Climate Desk collaboration.
In the summer of 2025, Iran experienced an exceptional heat wave that saw daytime temperatures approach 50 °C (122 °F) in several areas, including Tehran, temporarily closing government offices and banks. During this period, the main reservoirs supplying Tehran region reached a record low level and the water supply systems were under severe pressure. Until the beginning of November, the reservoir behind the Amirkabir dam, the main source of Tehran’s drinking water, had decreased to about 8% of its capacity. The current crisis reflects not only the extreme heat of this summer, but also several consecutive years of reduced rainfall and persistent drought conditions across Iran. As a result, Iran’s capital now faces a potential “Day Zero” when the taps could run dry.
Drought quickly disrupted Tehran’s urban systems. With dry soils and high evaporation, rivers and wetlands shrunk. The decrease in the level of reservoirs led to the disruption of hydropower production, and the lack of water led to saving measures in parts of the capital. Amid the mounting pressure, officials have warned that the capital city may even be evacuated if water supplies are not improved. In November, President Masoud Bezikian said the capital would have to be moved. These cascading effects showed how vulnerable Tehran’s infrastructure, economy and societies have become under the combined pressure of heat and drought.
These cascading effects are caused by the prolonged lack of precipitation in recent years (Figure 1a). Rainfall around Tehran usually peaks between December and April, and the reservoirs behind the dams are refilled before the onset of the dry summer. Over the past five years, rainfall in this wet period has consistently remained below the long-term climatological baseline, with the 2024–25 season showing the largest and longest deficit of the entire rainy season. When such prolonged drought was combined with an exceptionally hot summer, it intensified hydrological stress across the region.
