Vegetation effects on climate and building energy demand in cities

Excessive heat in cities exacerbated by urban heat islands can negatively impact human health, building energy consumption, and urban ecosystems. Increasing urban greenery has often been proposed as an attractive mitigation strategy as vegetation can reduce air and surface temperatures, solar radiation absorption by artificial surfaces, and modify local wind speed. However, vegetation can also lead to changes in humidity and turbulent dissipation of heat, effects that are generally not considered. These changes in local climate can influence the energy demand for cooling, dehumidification, and heating of building interiors. Yet, a systematic quantification of how vegetation in cities influences these different components and how this translates to building energy use in different climatic regions and for different building patterns is still lacking. Here, we combine ecohydrological and building energy modelling to simulate the direct and indirect effects of vegetation on urban microclimate and building energy demand. Specifically, we quantify the relative effects of urban vegetation on cooling, heating and dehumidification needs due to changes in outdoor air temperature and humidity, shade provision on building façades, and turbulent dissipation of heat in different climate zones. We further explore the effects of variation in vegetation type and urban neighborhood patterns. This knowledge is crucial to support planning of sustainable and climate resilient cities by maximizing the energy saving potential provided by urban vegetation.