İstanbul reservoir levels at highest in eight years after days of heavy rain

The average water level in İstanbul’s reservoirs has risen above 50% following days of heavy rainfall across the city, marking the highest level since 2018.

According to data from the İstanbul Water and Sewerage Administration (İSKİ), the average reservoir fill rate increased from 38.06% on Oct 14 to 52.43% on Oct 18, a rise of 14.37 percentage points in four days.

Water levels began rising after rainfall started on the evening of Oct 13, intensified on Oct 14 and continued over the following days.

The rainfall lead to floods in various parts of the city, causing the death of at least five people. At least two others are reported missing. Also, one person was killed in the neighboring province of Kocaeli.

Heaviest rainfall in decades

According to the İstanbul Metropolitan Municipality, the city recorded some of its heaviest rainfall in 84 years.

Rainfall was particularly heavy in the northern parts of the city. In Beykoz, it reached 277.1 kilograms per square meter, the highest level recorded since 1942.

Parts of the Bosphorus area and the districts of Sarıyer, Eyüpsultan, Arnavutköy, Şişli, Başakşehir, Büyükçekmece, Kâğıthane and Beykoz received between 130 and 277 kilograms of rainfall per square meter.

The rainfall recorded in Beykoz was nearly four times İstanbul’s long-term average for October.

Fill rates by dams

Reservoir fill rates varied considerably across the city. The highest levels were recorded at Elmalı (77.48%), Darlık (75.75%), Alibey (75.03%) and Istrancalar (70.48%).

Other reservoirs stood at Ömerli (66.62%), Terkos (36.67%), Sazlıdere (30.95%) and Büyükçekmece (30.18%). Pabuçdere and Kazandere remained at particularly low levels of 3.58% and 8.08%, respectively.

İstanbul has received a total of 572.12 million cubic meters of water from external sources this year, including 451.54 million cubic meters from Melen and 120.58 million cubic meters from Yeşilçay.

Meanwhile, the city’s drinking water treatment facilities have supplied 918.02 million cubic meters of water this year.

Total rainfall in the city’s reservoir catchment areas has reached 876.61 kilograms per square meter since the beginning of the year.

Reservoir levels over the past 10 years

According to İSKİ statistics, reservoir fill rates on Oct 18 stood at 41.35% in 2016, 52.66% in 2017, 53.63% in 2018, 45.4% in 2019 and 32.69% in 2020.

The corresponding figures were 47.58% in 2021, 44.25% in 2022, 21.29% in 2023, 34.38% in 2024 and 24.51% in 2025.

This year’s Oct 18 level of 52.43% is the third-highest recorded for that date over the past decade, behind only 2017 and 2018. (VC/VK)