Increasing vulnerability of urban climate to recent climate change

Recent global warming has intensified the urban heat island (UHI) effect and related temperature impacts in cities. The capital of the Czech Republic, Prague (c. 1.385 million inhabitants in 2023), with its long history of meteorological observations and dense network of meteorological stations, was analysed to assess changes in UHI and related temperature variables over the period 1921–2023. Long-term changes in mean (TAVG), maximum (TMAX), and minimum (TMIN) temperatures, along with temperature characteristics derived from them, showed predominantly significant increasing trends, except for the number of frost and ice days, which exhibited a decreasing tendency. Accelerated warming was particularly evident in the past two decades. During 1961–2023, the mean annual magnitude of Prague’s UHI was highest for TMIN and TAVG (1.8°C and 1.5°C respectively for the Klementinum station, and 1.7°C and 1.1°C respectively for the Karlov station), while it was relatively negligible for TMAX. Based on mean series from urban, suburban, and rural stations, the strongest intensification of UHI during the study period was observed in the summer and for TMIN. The daily UHI structure was characterised by the highest nocturnal positive and statistically significant temperature differences compared to rural surroundings, particularly on days with long sunshine duration and lower wind speeds, conditions conducive to intensified sensible heat flux. The highest TAVG and TMIN differences between Prague and its rural surroundings were recorded during anticyclonic circulation types, as opposed to directional and cyclonic types. Urban warming was generally more pronounced during circulation types with eastern and southeastern airflow compared to other airflow directions. 

Acknowledgements:  This research was supported by the Technology Agency of the Czech Republic for its financial support under the grant no. SS02030040 (Prediction, Evaluation and Research for Understanding National sensitivity and impacts of drought and climate change for Czechia, PERUN)