US and Iran reservoirs sink to perilous lows as drought tightens grip

Six major American reservoirs have fallen to their lowest late-May levels in at least three decades, according to federal monitoring data, a stark indicator of the deepening hydrological stress across the western United States. The Bureau of Reclamation’s dashboard, which compares current storage against records dating to 1990, flagged the dams this week, with the Colorado River Basin’s Lake Mead and Lake Powell among the most acutely affected. Viewed from Washington, the numbers signal not an anomaly but the continuation of a two-decade megadrought that has reshaped water allocation talks between seven states and Mexico. The reservoirs, which together underpin municipal supply, hydropower generation and irrigation for millions of hectares, are entering the dry summer months with buffers dangerously thin.

Half a world away, Iran’s capital is confronting a water deficit of equal gravity. Data released by the national water resources management company show that the five reservoirs serving Tehran began the current water year with just 250 million cubic metres in storage, compared with the 800 million required in a climatically average year. The shortfall follows a 30 per cent decline in precipitation across Tehran province, part of a wider pattern of low rainfall in catchments feeding dams in Qom, Alborz and Khorasan-e Razavi provinces. The Amir Kabir dam stood at 66 per cent full as of late May, but the neighbouring Lar dam had shrunk to a mere 8 per cent of capacity — a drop of ten percentage points from the same period last year. Officials have warned that the uneven distribution of rainfall across the interior basin near the Namak salt lake is leaving key reservoirs critically low as temperatures climb.

The synchronised strain on reservoirs in two geopolitically distant but climatically vulnerable zones underscores a broader shift in water security norms. Analysts in London note that the American Southwest and the Iranian plateau share a susceptibility to prolonged La Niña-driven dry spells, compounded by rising evaporative demand linked to global heating. In both cases, infrastructure built for a wetter past is being tested beyond its design assumptions. While the US has deployed a suite of institutional mechanisms — from interstate compacts to federal drought contingency plans — Iran relies heavily on centralised rationing and occasional inter-basin transfers that are themselves constrained by shrinking donor basins. The current situation revives memories of the severe Tehran water shortages of 2021, when rolling cuts triggered rare public protests.

Looking ahead, the margin for error is negligible. American water managers will release updated operational forecasts for the Colorado system in August, with the risk of further mandatory delivery cuts if monsoon rains disappoint. In Iran, authorities are already rationing supplies to agriculture east of Tehran and quietly exploring emergency groundwater pumping, a stopgap that risks accelerating land subsidence. The twin crises, though unfolding under distinct political and economic systems, point to a common truth: adaptation is no longer a matter of long-term planning but of day-to-day crisis management. For the tens of millions who depend on these stored waters, the summer of 2025 is shaping up as a stress test of the state’s capacity to keep the taps running.