The effects of extreme climatic events on urban trees in Mediterranean regions: A review

Mediterranean cities are home to more than 10% of the global population and more than 1298 urban tree species. These regions are highly vulnerable to climate change and are facing extreme climatic events such as droughts, heat waves, and flash floods. Urban trees play a key role in mitigating and reducing the effects of these events; however, it remains poorly understood how urban trees might cope with them. This review synthesizes the existing literature evaluating the effects of climatic and weather-related extremes on urban trees in Mediterranean cities. We screened more than 3000 studies, yet only 13 met the criteria of this review. Among the analyzed studies, most focused on drought and heat waves, with only one addressing the effects of extreme wind on tree mortality. Most studies employed remote sensing data and analytical methods, while a smaller number used experimental, field-based, or dendrochronological approaches. Since ten studies addressed droughts, the Standardized Precipitation–Evapotranspiration Index (SPEI) was calculated to contextualize and compare drought characteristics and outcomes across the analyzed cases. Our synthesis reveals that climatic extremes consistently impaired urban tree functioning across multiple scales and methods: remote sensing analyses detected declines in canopy greenness and cover, field-based studies documented reductions in leaf area and photosynthesis and simulation approaches highlighted the loss of evaporative cooling in irrigated trees under water restriction. Overall, the results reveal a significant and concerning research gap in understanding how climatic extremes might influence tree physiology, growth, and adaptive capacity within Mediterranean regions and urban environments. Advancing the knowledge of species and single tree level response to climatic extreme events is crucial for resilient urban forest management, particularly to inform sustainable tree species lists and help predict tree damage and failure, as well as sustain their provision of ecosystem services. • Out of 3,000+ screened studies, only 13 investigate the impact of extreme climatic events on urban Mediterranean trees, while 34 adopt an anthropocentric focus, examining trees through the lens of human exposure, risk, and benefit. • Climatic extremes reduce canopy cover, greenness, leaf area, photosynthesis, tree growth, and evaporative cooling. • Studies focus most on drought as a climatic extreme, using a wide variety of characterization indexes. • Remote sensing dominates the field, which is why most evidence reflects community-level responses rather than species or individual trees, which are crucial for practical applications that enhance the resilience of urban forests.