Modeling the impacts of building energy efficiency on the thermal microclimate in a midsize German city

Increasing building energy efficiency (BEE) is an established mitigation measure against climate change. However, it is currently less understood, if the implementation of increased BEE could have an impact on urban microclimate and therefore potentially interferes with adaptation efforts to climate change. In this modeling study, we tested the hypothesis that decreased thermal diffusivities of building facades due to building retrofitting will increase sensible heat fluxes at the facade surfaces and can therefore lead to an increase in urban heat exposure. Our modeling results conducted with the urban microclimate model ENVI-met for two different neighborhoods in the mid-sized city of Braunschweig, Germany indicate that retrofitting complete neighborhoods might lead to an increase in urban temperatures by up to 2.5 K locally and 1 K when spatially averaged at daytime. However, at night-time a cooling effect of almost the same magnitude is noted that could reduce the maximum of the urban heat island. Overall, it can be expected that a necessary increase in BEE standards due to their role in climate change mitigation lead to an increase in daytime outdoor heat exposure. Methods to alleviate this trade-off between climate change mitigation and adaptation should be studied in the future.