Tree-Canopy Cooling Attainment in European Functional Urban Areas

Abstract

Adaptation to urban heat requires scientific knowledge about the magnitude of the impact of existing vegetation-induced cooling on a certain thermal threshold and the resilience of such benefits in face of uncertainty. This article introduces a tree canopy cooling attainment calculation across 601 European FUAs in the EU-27 region. The methodological computation is based on July-August 2018 Landsat 8 OLI/TIRS land surface temperature, Copernicus tree cover density, PML V2 canopy transpiration-interception evaporation rates, Global Human Settlements population density in 2015, and model evaluation against 463 NOAA weather stations as in Marando et al. [16]. The computation translates FUA cooling into target attainment, reserves, tree cover shortage equivalent and population concordance. The average cooling attained in Europe is 1.07 ^∘C, while the range of cooling per FUA is approximately −0.4 to 2.9 ^∘C. Out of the total number of FUAs, 281 are still below 1 ^∘C, 208 reach 1 ^∘C cooling, and 112 reach 1.5 ^∘C and above, the reliable one-degree mark following the application of a 0.5 ^∘C allowance. The cooling target attainment thresholds using canopy as reference measure are: 16%, 32% and 48% tree canopy cover respectively for 1, 2 and 3 ^∘C cooling. Results from the model comparison showed that country-conditioned structural forms offer a better forecasting capability compared to universal models and the complete mixed effects form has the smallest RMSE and a relative improvement of 32.1% from the null model. On the population dimension, in 63% of the cases, more than half of the population live in positive-cooling FUAs while in 37% the opposite holds. These results suggest that European greening policy should differentiate between positive cooling, one-degree attainment, reliable reserves and population alignment.