Meteorological factors affecting the summer urban heat island in a Mediterranean coastal city - the case of Tel Aviv, Israel

In areas with a long summer season, especially where heat stress prevails throughout the day, such as Mediterranean coastal cities, Urban Heat Island (UHI) causes further thermal discomfort and an increase in energy consumption. Previous studies have indicated a pronounced UHI in stable winter nights, whereas most studies on the UHI in the warm season have focused on individual case studies. This study analyses the characteristics of the summer UHI of Tel Aviv under different weather conditions, using meteorological data over five summer seasons (2020-2024), and develops a statistical downscaling model that predicts the UHI intensity, based on synoptic- and mesoscale variables. The Tel Aviv UHI is quite variable during summer days, depending on mesoscale variations under the semi-permanent synoptic seasonal conditions. During daytime, the UHI is weak (<2°C) and occasionally negative. The nighttime UHI ranges from <1°C to extreme (9°C) and is typically between 4-7°C. The UHI intensity is significantly dependent on the westerly wind component, i.e., the sea breeze, enhanced by the synoptic-scale Etesian winds, the height of the persistent seasonal marine inversion, and the existence and intensity of a surface inversion, observed near the city. A prediction equation for the UHI yields a 0.85 correlation with the observed values. A surprising finding is an inverse relationship between the nocturnal temperature and the UHI intensity. In several excessive nocturnal heat events, with minimum temperature >26°C, the nocturnal UHI was minimal or even disappeared. These nights were characterized by an absence of the land breeze, increased nocturnal westerly winds from the warm Mediterranean Sea, and a relatively high base of marine inversion accompanied by clouds. However, during other nocturnal heat events, the UHI was distinct, and occasionally extreme, explained by the light land breeze, clear skies, and a pronounced surface inversion or a low marine inversion base.