Mapping urban heat islands and heat-related risk during heat waves from a climate justice perspective: A case study in the municipality of Padua (Italy) for inclusive adaptation policies

Climate change has led to a dramatic increase in extreme events worldwide. Predictions for a + 1.5 °C world indicate that 13.8% of the global population will be exposed to heat waves (HWs), a proportion rising to 36.9% in a + 2 °C scenario. At present, about 9.6 M people in the EU and UK are exposed to extreme heat every year. Overheating has various impacts on cities, including urban infrastructure failures and changes in ecological processes. However, scarce attention is currently paid to the distribution of HWs impacts and the differential vulnerabilities of different social groups, raising the issue of climate justice in cities. HWs directly impact the health of the most vulnerable social groups resulting in an increase in mortality and morbidity rates. This research focuses on the city of Padua (Italy) as a pilot study to assess the effects of urban HWs and heat islands (UHI) combined. By framing the unequal spatial distribution of socially vulnerable groups, this study aims to i) provide a replicable spatially explicit open-access methodology to assess the heat-related risk of UHI; ii) propose the first climate justice heat-related risk index to be adopted in inclusive and just adaptation plans. Specifically, it aims to i) identify HWs and map critical hotspots during summer 2022 at suburban scale; ii) assess the spatial correlations among impervious areas and UHI; iii) map the climate risk to vulnerable social groups; and iv) propose a global climate justice risk index for all the vulnerable groups considered. Images from Landsat 8–9 were processed, and territorial data were acquired from public databases. It was found that three extreme HWs hit Padua in summer 2022, on 2–7 June, 21–23 July, and 4–8 August, when maximum temperatures were 35.1 °C, 36.1 °C, and 35.8 °C, respectively. The intensity and magnitude of UHIs were considerable, with land surface temperatures of 33.8 °C on average (σ = 1.7, min = 27.9, max = 41.4). UHI intensity reached 5–8 °C of difference with rural contexts, mainly in strongly urbanized sectors. Ordinary least squares regression indicated a positive correlation with impervious surfaces, with a β coefficient showing an average increase of 0.3 °C per 10% of soil sealing. Six different hotspots were identified both in industrial areas and within the city centre. However, the integrated climate risk analyses highlight that most critical areas are in sectors where there is a large number of the elderly, migrants, children, and low-income households. Our findings reveal the need for urgent heat island mitigation measures and that the distributive dimension of climate justice should be respected in adaptation planning.