Why Tehran Is Running Out of Water

This story is original It appears in the Bulletin of the Atomic Scientists and is part of the Climate Desk collaboration.

During the summer of 2025, Iran experienced an exceptional heat wave, with daytime temperatures in several areas, including Tehran, approaching 50 °C (122 °F) and forcing the temporary closure of public offices and banks. During this period, the main reservoirs supplying the Tehran region reached record low levels, and water supply systems came under severe pressure. By early November, the level of the reservoir behind the Amirkabir Dam, Tehran’s main source of drinking water, had fallen to about 8 percent of capacity. The current crisis reflects not only the extreme heat this summer, but also several consecutive years of low rainfall and persistent drought conditions across Iran. As a result, the Iranian capital now faces a potential “day zero” when the taps run dry.

Drought quickly disrupted Tehran’s urban systems. As the soil dried out and the rate of evaporation increased, rivers and wetlands shrank. Low reservoir levels have disrupted hydroelectric power generation, and water shortages have prompted drastic conservation measures in parts of the capital. Amid this mounting pressure, officials have warned that the capital may have to be evacuated if water supplies fail to recover. In November, president Masoud Pezeshkian said the capital should be moved. These cascading impacts have revealed how vulnerable Tehran’s infrastructure, economy and communities are under the weight of worsening heat and drought.

These cascading effects stem from prolonged rainfall deficits in recent years (Figure 1a). Rainfall around Tehran usually peaks between December and April, replenishing reservoirs behind dams before the onset of dry summer. Over the past five years, rainfall during this wet period has remained consistently below the long-term climatological baseline, with the 2024-2025 season showing the most pronounced and long-lasting deficit across the entire rainy season. When this prolonged drought was followed by an exceptionally hot summer, it exacerbated hydrological stress throughout the region.