A hydrological-energy balance model to assess land surface temperature at the urban scale: the case study of Milano, Italy

This work provides a physical based approach to assess Land Surface Temperature (LST) at urban context, to analyze the Surface Urban Heat Island Intensity (SUHII).  We developed and tested a hydrological-energy balance model, Poli-HE, to compute surface energy, and mass fluxes between soil surfaces, and shallow atmospheric layers in the city of Milan, Italy. Land Surface Temperature (LST) was calculated under given climate conditions and land cover, and spatially distributed with a resolution of 500 m. For mixed paved/green pixels, Vegetation Fraction (VF) was applied. Energy and water balances were integrated, linking soil moisture and latent heat flux to LST. Due to rapid global urbanization, average temperatures in cities have risen more than in the surrounding areas. The temperature difference between urban and rural areas refers to the Surface Urban Heat Island (SUHI) phenomenon. During summer, where LST is in Milan is about 35 °C, paved and green surfaces differ by about + 3.7 °C, reaching up to +4.5°C at times. The Poli-HE outcomes indicate that the presence of green areas can provide a cooling effect and reduce LST, as also shown by satellite observations. In particular, it was proved that an increase of ΔVF = +10% corresponds to a decrease of ΔLST = -0.26°C. This quantitative approach could support urban authorities and professionals, providing a practical tool for current and future planning and projects within the framework of national and international adaptation and mitigation measures.