Istanbul’s dam occupancy rate has fallen to 48.13% as declining rainfall, hot weather and increased summer water consumption continue to reduce the city’s water reserves, according to recent data from the Istanbul Water and Sewerage Administration (ISKI).
The city’s dams reached their highest occupancy level of the year at 72.05% on May 11. By Aug. 19, the level had dropped to 48.13%.
Elmalı Dam has the highest occupancy rate at 78.42%, followed by Ömerli Dam at 68.9% and Darlık Dam at 66.24%. At the other end of the scale, Pabuçdere Dam stands at 14.45%, while Kazandere Dam is at 20.87% and Sazlıdere Dam at 27.19%.
The dams and reservoirs supplying Istanbul have a combined storage capacity of 868.68 million cubic meters (704,200 acre-feet), with 420.56 million cubic meters (341,000 acre-feet) currently stored.
The city is also supplied through the Melen and Yeşilçay water systems, which have provided 492.7 million cubic meters (399,400 acre-feet) of water so far this year.
Meteorologist warns of further decline
Güven Özdemir, a meteorological engineer and faculty member at Istanbul Aydın University, warned that water levels could fall further if hot weather persists through Aug. 24-25.
Özdemir said high temperatures and strong winds could increase evaporation, putting additional pressure on the city’s water reserves.
He said rainfall from September onward will be important for replenishing the dams, noting that intermittent rainfall is possible through the end of August. However, he said rainfall of around 20 to 30 millimeters (0.8 to 1.2 inches) would be needed to make a meaningful contribution to reservoir levels.
Özdemir warned that dam occupancy falling to around 20% would mark a critical period and urged residents, institutions and municipalities to prioritize water conservation.
He also pointed to declining rainfall patterns and the impact of Istanbul’s urban heat island, saying persistent high-pressure systems and extreme heat are accelerating the decline in water levels.
While rainfall is expected to increase in September, Özdemir said the amount remains uncertain and warned that sudden, localized downpours could trigger flooding.
He said it is too early to make detailed long-term forecasts but stressed that water consumption should be minimized under current conditions.
Özdemir also called for more efficient irrigation of public green spaces, urging municipalities to repair faulty sprinkler systems and avoid unnecessary watering. He said irrigation should preferably take place before sunrise or after sunset to reduce water loss through evaporation.