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

Haider Taha

doi:10.3390/cli5030059

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 km2). 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.

Highlights

Urban heat, often quantified as urban heat island (UHI), can locally exacerbate the effects of regional climates on heat, emissions, and air quality [1,2,3,4,5]
There was an increase of 9% in mortality for every 5.5 ◦ C increase in the apparent temperature [25]
Californian the cumulative totals were converted to degree-hour per day (DH/day) averages, as in

Summary

Introduction

Often quantified as urban heat island (UHI), can locally exacerbate the effects of regional climates on heat, emissions, and air quality [1,2,3,4,5]. The exacerbation has significant ramifications in terms of public health from both heat and air-quality pathways [6,7,8]. The cooling energy demand increases, emissions of anthropogenic and biogenic pollutants (e.g., ozone precursors) increase, the photochemical production of ozone accelerates, and air quality (O3 , PM10/2.5 , NOx ) deteriorates [9,10,11,12,13]. Some UHIs can be as high as 8 ◦ C, e.g., in tropical regions [14,15], but this is rather atypical. UHIs are in the order of 0.5 to 3 ◦ C [8]

Methods

Results

Conclusion