Characterization of Urban Heat and Exacerbation: Development of a Heat Island Index for California

Abstract

Abstract:To further evaluate the factors influencing public heat and air-quality health, a characterization of how urban areas affect the thermal environment, particularly in terms of the air temperature, is necessary. To assist public health agencies in ranking urban areas in terms of heat stress and developing mitigation plans or allocating various resources, this study characterized urban heat in California and quantified an urban heat island index (UHII) at the census-tract level (~1 km 2 ). Multi-scale atmospheric modeling was carried out and a practical UHII definition was developed. The UHII was diagnosed with different metrics and its spatial patterns were characterized for small, large, urban-climate archipelago, inland, and coastal areas. It was found that within each region, wide ranges of urban heat and UHII exist. At the lower end of the scale (in smaller urban areas), the UHII reaches up to 20 degree-hours per day (DH/day; • C.hr/day), whereas at the higher end (in larger areas), it reaches up to 125 DH/day or greater. The average largest temperature difference (urban heat island) within each region ranges from 0.5-1.0 • C in smaller areas to up to 5 • C or more at the higher end, such as in urban-climate archipelagos. Furthermore, urban heat is exacerbated during warmer weather and that, in turn, can worsen the health impacts of heat events presently and in the future, for which it is expected that both the frequency and duration of heat waves will increase.

Progress in Urban Greenery Mitigation Science – Assessment Methodologies Advanced Technologies and Impact on Cities

“…The fact that cooler air can be advected away from vegetation over significant distances is important in benefiting a larger area and reducing temperaturedependent biogenic and anthropogenic emissions not only in the canopy vicinity but also in the non-vegetated surroundings (Taha 2015b). Such length scales, or "fetch", for cool-air transport are a function of wind speed (Taha et al 2018) and can be used as a basis for establishing the various heat-island mitigation modeling and implementation levels (Taha 2017).…”

“…Some such thinking in this direction already is underway (e.g. Taha 2017;Taha et al 2018;Zhang et al 2017;Reeve et al 2015;Jim 2013;Jennings et al 2016 among others). Thus far, most studies demonstrate that there is great potential for urban greening to improve microclimate and air quality if all of the various site-specific physical and chemical processes are factored in during the design of mitigation measures.…”

Urban heat resilience at the time of global warming: evaluating the impact of the urban parks on outdoor thermal comfort

“…Climate change has had visible effects on many human communities all over the world, but these effects are more deeply felt in large, densely populated cities (IPCC, 2019;Bulkeley, 2013). Research has shown that urban areas are typically warmer than their rural counterparts; a difference that can be attributed to the phenomenon known as urban heat island effect (UHI) (Ward et al, 2016;Oke, 1982;Taha, 2017). This effect is strong enough to cause major physical and mental health problems for citizens (Luber & McGeehin, 2008;Tan et al, 2010;Lemonsu et al, 2015;Błażejczyk et al, 2018).…”

The Cooling Effect of Large-Scale Urban Parks on Surrounding Area Thermal Comfort

“…Today, heat has adversely affected urban life across the world [3], including urban areas of the Mediterranean climate [4,5]. The increase in temperature in urban areas, especially densely populated areas has given rise to the phenomenon of urban heat islands (UHI) [6,7], which can threaten the health and comfort of citizens [8,9]. The green urban spaces have been researched by numerous studies as an adaptive strategy to reduce the effect of urban heat and improve the health of citizens, by considering thermal comfort [10,11] as well as their socio-economic role [12].…”