This story originally appeared Bulletin of the Atomic Scientists and is part of it Climate office cooperation.
In the summer of 2025, Iran experienced an exceptional heatwave, with daytime temperatures reaching 50 degrees Celsius (122 degrees Fahrenheit) in several regions, including Tehran, forcing temporary closure offices and banks. During this period, the main reservoirs supplying the Tehran region reached record low levels, a water supply systems have come under serious strain. In early November, the level of the reservoir behind the Amir Kabir Dam, Tehran’s main source of drinking water, dropped to approximately 8 percent of its capacity. The current crisis reflects not only this summer’s extreme heat, but also several consecutive years of reduced rainfall and ongoing drought in Iran. As a result, Iran’s capital is now facing a potential “day zero” when taps could run parched.
The drought quickly disrupted Tehran’s urban systems. In parched soils and high evaporation, rivers and wetlands have shrunk. This led to a decline in reservoir levels disruptions to hydropower generationand water shortages prompted stringent austerity measures in some parts of the capital. In the face of mounting pressure, officials warn that the capital may even we need to evacuate if water supplies are not restored. In November, President Masoud Pezeshkian announced that the capital would do so need to be moved. These cascading effects have highlighted how vulnerable Tehran’s infrastructure, economy and communities have become in the face of mounting stress from heat and drought.
These cascading effects result from the prolonged rainfall deficit in recent years (Figure 1a). Rainfall around Tehran usually peaks between December and April, refilling reservoirs behind the dams before the onset of the parched summer. Over the past five years, rainfall during this moist period has remained consistently below the long-term climatic baseline, with the 2024-25 season showing the most pronounced and prolonged deficit of the entire moist season. When such a long drought was followed by an exceptionally sizzling summer, it intensified hydrological stress across the region.