Human heat health index (H3I) for holistic assessment of heat hazard and mitigation strategies beyond urban heat islands

Certain urban neighborhoods are more susceptible to heat than others, primarily because of the unequal distribution of imperviousness, building and vegetation morphology, social vulnerability, and anthropogenic heat release. Here, we demonstrate that using the surface urban heat island intensity obtained through remote sensing approaches to evaluate urban heat vulnerability (UHV) can be misleading due to the interannual and seasonal variability of rural land surface temperature (LST). We present the disparity in the heat vulnerability index (HVI) when LST and air temperature are used as hazards and show that the LST-based approach overestimates the HVI during daytime. Thus, we contend that while HVI may be appropriate for comparing the relative UHV of different neighborhoods, it should not be used to assess absolute daytime heat vulnerability. To address this limitation, we propose a new metric: human heat health index (H3I) that can be utilized to (i) assess and compare heat hazard in different neighborhoods and (ii) evaluate the effectiveness of environmental interventions for heat mitigation. H3I was applied to demonstrate the reduction in heat hazard due to 3-D urban structures using street-level modeling in Austin, Texas. Our findings emphasize the need for combining 3-D urban data, modeling, and community feedbacks efforts to assess daytime UHV for prioritizing the implementation of heat mitigation strategies.