The compound effect of climatic extremes on the 2025 Sakarya wildfire in Türkiye: A remote sensing assessment in a humid–Mediterranean climate transition zone

The western and southern regions of Türkiye are strongly influenced by the Mediterranean thermal regime during the summer season, with prolonged summer drought representing one of the defining characteristics of the Mediterranean climate. Over the last decade, both the frequency and intensity of drought and extreme heat events have increased. In particular, the summer of 2025 was drier than long-term climatological normals. At the same time, increasing influence of climate change has intensified the frequency and severity of compound climatic extremes, substantially increasing wildfire risk, within climate transition zones. Under these exceptionally hot and dry atmospheric conditions, environmental settings became highly favorable for wildfire ignition and rapid-fire spread, such that even minor physical or anthropogenic disturbances were sufficient to trigger wildfire. This study investigates the relationship between compound climatic extremes and large-scale 2025 wildfires in Sakarya. Meteorological analyses were conducted using long-term daily temperature, relative humidity, wind speed, and precipitation. Heatwave characteristics were evaluated using the HWN, HWDx, and HWMn indices, while drought were assessed using the SPI. In addition, Sentinel-2 images and GEE platform were employed to evaluate post-fire vegetation damage and burn severity through dNDVI, dNDMI, and dNBR indices. The findings reveal that fire days were strongly associated with compound extreme conditions characterized by above-threshold maximum temperatures and low relative humidity. Prolonged drought observed during pre-fire period further intensified fuel dryness and wildfire susceptibility. Remote sensing analyses indicate that substantial reductions in vegetation density, moisture content, and ecosystem functionality within burned areas. In conclusion, satellite-based dNBR analyses indicate that approximately 20,000 hectares of land were affected by the 2025 wildfires in Sakarya. The findings demonstrate that these wildfire events were associated not with a single meteorological factor alone, but rather with the interaction of heatwaves, prolonged drought and compound hot–dry atmospheric processes. These results clearly indicate that climate change has become an increasingly important factor in the occurrence and spread of wildfires, particularly within climate transition zones. The study provides important scientific evidence for improving wildfire early warning systems, strengthening regional climate adaptation policies, and developing sustainable wildfire management strategies under future climate change scenarios.