Heatwaves and urban heat islands: A comparative analysis of multiple cities

Abstract

The recent International Panel on Climate Change report predicts the highly urbanized Northeastern U.S. to be at high risk to heat waves. Since urban residents and infrastructure are known to be highly vulnerable to extreme heat, the goal of this paper is to understand the interaction between the synoptic‐scale heat wave and the city‐scale urban heat island (UHI) effects. The study also qualitatively analyzes the primary factors that contribute to UHIs by comparing their intensities in different cities with distinct geo‐physical characteristics. Our results, generated by using the Weather Research and Forecasting model augmented with advanced urban surface parameterizations, confirm that the amplitude of UHI is related to the physical size of the city. However, the results suggest that cities of comparabale sizes might interact differently with heat waves: in New York City; Washington, DC; and Baltimore (but not in Philadelphia) the regular UHI was amplified more strongly during heat waves compared to smaller cities. The results also establish that the pattern of UHI in different cities, its variability, and its interaction with heat waves are inherently linked to dynamic factors.

New York City Panel on Climate Change 2019 Report Chapter 2: New Methods for Assessing Extreme Temperatures, Heavy Downpours, and Drought

“…These effects include increasing energy demand (Schaeffer et al, 2012;Sailor, 2001;Santamouris, 2014) and mortality (Knowlton et al, 2007;Luber and McGeehin, 2008;Anderson and Bell, 2010;Rosenthal et al, 2014). Moreover, higher temperatures associated with urbanization, a phenomenon called the Urban Heat Island (UHI) (Oke, 1982), exacerbate the impacts of extreme heat events (Li and Bou-Zeid, 2013;Ramamurthy and Bou-Zeid, 2016;Ramamurthy et al, 2017;Ortiz et al, 2018).…”

“…An example of these processes is the soil moisture-heat wave feedback, wherein dry soil conditions may amplify heat waves by reducing available moisture for evaporative cooling (Seneviratne et al, 2006;Lorenz et al, 2010;Fischer et al, 2007). Cities may amplify these feedbacks by reducing exposed soil area, greatly reducing the capacity for water retention near the land surface (Li and Bou-Zeid, 2013;Ramamurthy and Bou-Zeid, 2016;Ramamurthy et al, 2017).…”

Contrasting changes of urban heat island intensity during hot weather episodes

“…At first glance, seemingly contradictory results concerning effects of heat waves, or more generally, HWEs, onto UHIIs are reported. While some studies show increasing UHIIs (Fenner et al 2014, Li et al 2015, Founda and Santamouris 2017, Ramamurthy and Bou-Zeid 2017, Zhao et al 2018, others reveal unchanged or even reduced UHIIs (Zhou and Shepherd 2010, Scott et al 2018, Rogers et al 2019. Several reasons have been put forward to explain these results, mainly relating them to changes in weather conditions, such as increased radiative input or altered wind patterns (Li et al 2016, Founda and Santamouris 2017, Sun et al 2017, Scott et al 2018.…”

Enhanced sensitivity of the urban heat island effect to summer temperatures induced by urban expansion

“…The difference between urban and rural areas in evaporation and anthropogenic heat release contributes to the enhanced UHI effect during heatwaves compared to normal days. Such a phenomenon is found in a wide range of cities (Li et al 2015, Schatz and Kucharik 2015, Ramamurthy and Bou-Zeid 2017, Tewari et al 2019. Considering that the heat risks in urban areas are closely relevant to background temperature and the UHI intensity (Gabriel and Endlicher 2011), it is necessary to investigate the relationship between temperature and the UHI effect (T-UHI).…”