Urbanization Amplifies Nighttime Heat Stress on Warmer Days Over the US

Abstract

Urbanization is the most tangible local-scale impact of humans on the Earth's surface and the surface climate (Jia et al., 2020;Kalnay & Cai, 2003). Urbanization-associated perturbations in land use/land cover (LULC) can substantially alter the micro-climate of cities via re-adjustment of the surface energy balance. Specifically, urban regions are observed to be warmer (based on temperature measured at 2 meter) and drier (based on moisture mixing ratio at 2 meter) than peripheral rural areas, commonly referred in the literature as Urban Heat Island (UHI) (e.g., Oke and Cleugh., 1991) and Urban Dry Island (UQI) (Oke & Cleugh, 1987), respectively. Along with LULC changes, urbanization is also associated with increases in the heat generated by anthropogenic activities or anthropogenic heat flux (AHF) into the urban atmosphere. Notably, the global urban population has crossed ∼4 billion (half of the total global population) and is expected to reach up to ∼7 billion, accounting for two-third of the total global population, by 2050 (Ritchie & Max, 2018). The human body's ability to dissipate metabolic heat through evaporative cooling (sweating) and heat conduction is inversely proportional to the ambient temperature and humidity (Sherwood & Huber, 2010). Consequently, urbanization-induced perturbations in micro-climate can substantially affect a large portion of the global population in the near future via urban-induced heat stress intensity (UHSI) and its associated economic impacts (

The Extreme Heat Wave of Summer 2021 in Athens (Greece): Cumulative Heat and Exposure to Heat Stress

“…Nighttime temperatures during the event were much higher in Athens compared to non-urban stations, due to the additive effect of the urban heat island phenomenon, in contrast to daytime temperatures, which were higher at several continental sites of the country (Table 2). This confirms previous findings suggesting strong synergies between UHIs and severe HWs, evident in nighttime rather than daytime temperatures [45,56,60]. During severe HWs, large-scale synoptic processes and strong anomalies in the upper and lower atmosphere overwhelm mesoscale or local effects, such as UHIs, during the daytime, in contrast to nighttime, when built environments release the absorbed heat.…”

“…However, the average UHI intensity was 7.7 ± 0.9 • C (peaking up to 9 • C) during HW2021, suggesting an amplification of the UHI intensity by 2-3 • C during the episode. These results confirm the findings of previous studies, reporting positive synergies between UHIs and HWs, which result in the amplification of UHI magnitude under exceptionally hot conditions, especially during nighttime [45,56,60].…”

Impacts of Large‐Scale Urbanization and Irrigation on Summer Precipitation in the Mid‐Atlantic Region of the United States

“…Land type data and anthropogenic heat fluxes are the same as Sarangi et al. (2021). Figure S1a in Supporting Information shows a simplified land cover map in which similar land cover types are combined.…”

“…Initial and lateral boundary conditions and time-varying sea surface temperature, vegetation fractions, and surface albedos are from the National Centers for Environmental Prediction (NCEP) North American Regional Reanalysis (NARR) product (Mesinger et al, 2006). Land type data and anthropogenic heat fluxes are the same as Sarangi et al (2021). Figure S1a in Supporting Information S1 shows a simplified land cover map in which similar land cover types are combined.…”

Detection and Attribution of Human Influence on the Global Diurnal Temperature Range Decline

“…The negative effect of OANT could be explained by the differential response of daytime and nighttime temperature to land use change (Mohan & Kandya, 2015; Ren & Zhou, 2014). For example, the urban heat island effect on rising temperature is much stronger during nighttime than daytime (Sarangi et al., 2021; Yang et al., 2017). NAT has weak impacts on global DTR changes, leading it to increase by 0°C and 0.02°C according to the two‐way and four‐way analyses, respectively.…”