Urban heat island and heat waves characteristics and interactions: a review of the state-of-the-art

Urban heat island (UHI) is a phenomenon associated to the different temperature diurnal cycle of the urban and surrounding rural environment, typically leading to higher air temperature in cities during the night. Heat waves (HWs) are intended as a climate related phenomenon associated to persistent high-pressure systems leading to high air temperature over a region for several days. The last IPCC report has highlighted that exacerbation of heat waves in future years will require specific attention for the consequences on urban heat islands, given that most cities and especially in the North-American continent, will experience more intense heat waves which may lead to intense UHI. Investigation of the synergy between HW and UHI is relevant in future years in order to set-up strategies to mitigate risks of extreme heat, water scarcity, energy requirements, enhancement of air pollution and many other aspects. The topic of the inteplay between the two phenomena is relatively recent and currently it is not entirely understood. Many studies report partially incoherent outcomes, assessing both the existence and the absence of a synergistic behaviour exacerbating the urban-rural temperature difference during HWs. In this talk we will review the hypotheses and theories explaining the dynamical nature of UHI and HWs in isolation together with progress made by our group in modelling and interpreting those phenomena. We will then discuss current methodologies used to investigate the interplay between the two based on both numerical studies and measured data analyses.