Long-term spatio-temporal assessment of thermal comfort in Antalya (Türkiye) using the Universal Thermal Climate Index (UTCI)

Climate change and the increasing frequency of extreme heat events have intensified thermal stress, particularly in Mediterranean regions, posing significant challenges to human health, quality of life, and sustainable urban development. Therefore, accurate assessment of outdoor thermal comfort has become increasingly important for supporting climate adaptation and planning strategies. This study aims to investigate the long-term (2000–2025) spatio-temporal changes of thermal comfort in Antalya (Türkiye) using the Universal Thermal Climate Index (UTCI). In addition, the performance of different interpolation methods was compared using Leave-One-Out Cross-Validation to identify the most appropriate approach for UTCI mapping. Monthly mean air temperature, wind speed, and relative humidity data from 21 meteorological stations operated by the Turkish State Meteorological Service were used. As long-term mean radiant temperature observations were unavailable, this variable was derived from the ERA5-Land reanalysis dataset. UTCI values were calculated using the BioKlima 2.6 software package. UTCI surfaces were generated by interpolating station-based UTCI values, and Leave-One-Out Cross-Validation identified the Elevation Regression method as the most accurate spatial interpolation approach. The results reveal a pronounced seasonal cycle in thermal comfort across Antalya, strongly controlled by the elevation gradient extending from the Mediterranean coast to the Western Taurus Mountains. Six UTCI thermal stress classes were identified throughout the year. Spring and especially autumn were dominated by no thermal stress conditions, whereas cold stress prevailed over the high mountain ranges during winter. In contrast, moderate and strong heat stress became widespread along the coastal belt during summer, particularly in the central districts of Antalya and the coastal districts of Serik, Manavgat, and Kemer. These findings provide valuable scientific evidence for climate change adaptation, sustainable tourism management, public health planning, and the integration of thermal comfort into spatial planning practices.