Quantifying evapotranspiration and shading cooling of urban vegetation across climates under extreme heat using an integrated SCOPE-SEB model and surface temperature analysis

Urban vegetation mitigates heat through evapotranspiration (ET) and shading, and quantitatively characterizing these two pathways is essential for comparable cross-city assessment and for identifying climate-specific limiting factors. However, a standardized and physically based framework to quantify and compare these cooling effects across different cities and climatic contexts is still lacking. Existing metrics, such as evapotranspiration-induced cooling of vegetation (ECoV) and shading-induced cooling of vegetation (SCoV), are typically applied within individual cities. To address this, we developed a transferable framework that integrates a physically based Soil-Canopy-Observation of Photochemistry and Energy (SCOPE) – Surface Energy Balance (SEB) model for evapotranspiration-related cooling with surface temperature analysis for shading-related cooling. Evapotranspiration-related cooling ( ΔT LE ) is quantified through the SCOPE–SEB framework, whereas shading-related cooling ( ΔT Shade ) is independently derived from surface temperature contrasts, enabling consistent cross-city comparison under extreme heat conditions. We evaluated the model at eddy-covariance flux towers in four mid-latitude cities representing hot-desert (Phoenix, Las Vegas) and Mediterranean (Rome, Florence) climates. The model demonstrated strong performance: turbulent heat fluxes (sensible, H, and latent, LE ) were reconstructed with R 2 = 0.56–0.78, while surface temperature ( T s ) was simulated with R 2 = 0.47–0.95. Modeled aerodynamic resistance showed lower agreement with tower-derived estimates and decreased with increasing wind speed. Crucially, the model achieved robust energy balance closure, with residuals of only ∼3–7%. Specifically, we revealed that: (1) The magnitude of daytime ΔT LE was greater in Mediterranean cities (−1.98 °C) than in hot-desert cities (−1.34 °C), whereas daytime ΔT Shade was significantly stronger in Mediterranean cities (−2.60 °C vs. -0.90 °C). Spatially, deserts exhibited extensive daytime warming patches in ΔT Shade and lower heterogeneity in ΔT LE , contrasting with the widespread, strong cooling and higher intra-urban variability of Mediterranean cities. (2) The primary controls were climate-dependent: cooling in water-limited deserts was dominated by soil moisture and leaf water/chlorophyll content, whereas in Mediterranean cities, canopy structure (height, LAI) governed both ΔT LE and ΔT Shade , with meteorology playing a secondary modulating role. This mechanism-explicit, physically consistent framework provides a transformative tool for cross-city comparison of vegetation-based heat mitigation, enhancing our understanding of climate-dependent ecosystem services.