Comparative quantification of local climate regulation by green and blue urban areas in cities across Europe

Urban growth alters environmental conditions with major consequences for climate regulation and the exposure of population to heat. Nature-based solutions may be used to alleviate the increasing urban climate pressures, but the climate regulation services that these solutions can supply for and across different urban conditions remains understudied. We comparatively investigate the urban ecosystem service realization (considering the ecosystem service supply and demand spatial interactions) of local climate regulation by vegetated (green) and water-covered (blue) areas across 660 European cities. Results show relatively robust power-law relationships with city population density (average R(2) of 0.34) of main indicators of ecosystem service realization. Country-wise fitting for city-average indicators strengthens these relationships, in particular for western European cities (average R(2) of 0.66). Cross-city results also show strong power-law relationship of effectiveness in ecosystem service realization with socio-economic measures like Human Development Index and GPD per capita, in particular for the area fraction of city parts with high ecosystem service realization (R(2) of 0.77). The quantified relationships are useful for comparative understanding of differences in ecosystem services realization between cities and city parts, and quantitative projection of possible change trends under different types of city growth so that relevant measures can be taken to counteract undesirable trends.