Drought Slashes Cooling Power of Urban Street Trees in Mediterranean Cities

Urban street trees in Mediterranean cities lose much of their ability to cool the air during simultaneous heat waves and droughts, according to new research. The study highlights how lack of soil moisture severely restricts plant transpiration—the process by which trees release water vapor and cool their surroundings. During extreme heat events, when cooling is most needed, drought-stressed trees provide significantly less thermal relief. The findings have major implications for urban planners and policymakers in cities like Barcelona, Athens, and Rome, where climate change is expected to increase the frequency of compound hot-dry events. While trees are widely promoted as a nature-based solution to urban heat, their effectiveness depends on adequate water supply. Without irrigation or drought-tolerant species selection, the cooling benefits of street trees may be unreliable just when they matter most. The research underscores the need for integrated water management and resilient urban forestry strategies to maintain livable cities in a warming world.