Temporal trend of the frequency and maximum durations of surface urban heat islands over global cities

The spatial pattern of the frequency and maximum duration of the surface urban heat island (SUHI) has been extensively studied. However, the long-term temporal trends of frequency and maximum duration of the SUHI (SUHIF and SUHID) on a global scale remain largely unexplored. This study investigates the variations and controls of SUHIF and SUHI trends for the period 2005 to 2022 over 1162 global cities, by combining the globally available seamless daily land surface temperature products, interpretable machine learning-LightGBM and SHAP algorithm. The global mean SUHIF trend between 2005 and 2022 is 0.63 f 1.39 days/year for the day and 0.51 f 1.31 days/year for night. Cities exhibiting a relatively high SUHIF trend are predominantly situated in Asia, while cities displaying a relatively low SUHIF trend are primarily located in Europe. The global mean SUHID trend is 1.68 f 2.93 days/year during the day and 0.52 f 1.58 days/year at night. The geographical distribution of the SUHID trend is analogous to that of the SUHIF condition. The global SUHIF and SUHID trends are mainly controlled by the background climate and surface properties. These findings are valuable in providing insights that can inform the development of heat mitigation strategies.