A joint study conducted by researchers from two Turkish universities and a U.S. institution has found that heat waves have increased significantly across Istanbul, Ankara and Izmir, western Türkiye, over the past century, while cold spells have become less frequent, highlighting the growing impact of climate change on Türkiye's largest metropolitan areas.
Scientists from Istanbul Technical University (ITU), Samsun University (SAMU) and the University of Missouri analyzed long-term meteorological records from 15 weather stations located across the country's 3 largest cities. The study examined daily maximum and minimum temperature observations collected between 1926 and 2024, with some stations providing nearly 100 years of continuous data.
The findings showed that heat waves increased at 11 of the 15 stations at statistically significant levels, while none recorded a significant decline. All 5 stations in Istanbul experienced a marked rise in heat wave frequency, with some of the strongest increases observed at Sarıyer and Şile.
In Ankara, the most notable increase occurred in Polatlı, followed by Nallıhan and Esenboğa Airport. In Izmir, Selçuk and Bergama recorded the sharpest increases, while an upward trend was also observed in Ödemiş, although it did not reach statistical significance.
Researchers found that the frequency of heat waves increased by approximately 0.14 to 0.78 additional heat wave events per decade, depending on the meteorological station.
Cold spells, meanwhile, declined across most locations. None of the stations showed a statistically significant increase in cold wave frequency, while the steepest decreases were recorded at Kadıköy Rıhtım and Florya in Istanbul and at Selçuk and the Izmir Regional station.
The decline in cold spells ranged from roughly 0.17 to 0.59 events per decade. The study also found statistically significant increases in annual average temperatures at every station, with warming rates ranging between 0.20 and 0.50 degrees Celsius per decade. The strongest warming trends were recorded in Selçuk and Polatlı.
Researchers found that heat waves were concentrated mainly during summer, but their occurrence in autumn suggests that periods of extreme heat are expanding into transitional seasons. Cold spells remained primarily winter events, although fewer were recorded during spring and autumn, indicating that cold weather risks are diminishing without disappearing completely.
Most heat waves and cold spells lasted between 3 and 7 days, though prolonged events lasting more than 10 days were also documented. Cold spells in Ankara generally lasted longer than those in the coastal cities, a difference researchers linked to the capital's continental climate, higher elevation and stronger nighttime cooling.
Researchers further examined how urban development influences local temperatures using the Local Climate Zone classification. They found that densely built urban areas retain heat absorbed during the day and release it overnight, increasing minimum temperatures, intensifying heat waves and reducing the likelihood of cold spells.
Research assistant Yiğitalp Kara said the findings demonstrate that climate change is becoming increasingly evident in Türkiye's urban environments.
"Our analyses show that average temperatures are rising, resulting in more frequent and more intense heat waves, while cold spells are declining," Kara said, warning that the changes could have significant consequences for millions of people living in large cities.
He stressed that heat waves should not be viewed solely as meteorological events because they affect public health, energy demand, transportation, agriculture, working conditions and urban infrastructure. Older adults, children, people with chronic illnesses and outdoor workers are among the groups most vulnerable to prolonged periods of extreme heat.
The findings come as much of Europe grapples with an intense early summer heat wave that has pushed temperatures above 40 degrees Celsius (104 degrees Fahrenheit) in several countries, fueling wildfires, straining healthcare systems and contributing to a rising death toll.
