Abstract
Future heat stress under six future global warming (ΔTGW) scenarios (IPCC RCP8.5) in an Asian megacity (Osaka) is estimated using a regional climate model with an urban canopy and air-conditioning (AC). An urban heat ‘stress’ island is projected in all six scenarios (ΔTGW = +0.5 to +3.0 °C in 0.5 °C steps). Under ΔTGW = +3.0 °C conditions, people outdoors experience ‘extreme’ heat stress, which could result in dangerously high increases in human body core temperature. AC-induced feedback increases heat stress roughly linearly as ΔTGW increases, reaching 0.6 °C (or 12% of the heat stress increase). As this increase is similar to current possible heat island mitigation techniques, this feedback needs to be considered in urban climate projections, especially where AC use is large.
Highlights
In 2018, Japan had the second hottest July on record (since 1883, Japan Meteorological Agency (JMA) official home page: https://www.data.jma.go.jp), with a mean monthly temperature in Osaka 1.63 °C higher than the 11 year (July 2000–2010) mean
Universal Thermal Climate Index (UTCI) increase (ΔUTCI) with global warming (ΔTGW) The UTCI is greater in Osaka than in the surrounding land areas at 05:00 under all seven climates (current and six future scenarios, figures 4(a)–(g)), we refer to these as urban heat ‘stress’ islands
Effects of greenhouse gas (GHG)-induced global warming on heat stress are considered by analysing regional climate model (RCM) dynamically downscaled simulatons for current and six future climate scenarios
Summary
In 2018, Japan had the second hottest July on record (since 1883, Japan Meteorological Agency (JMA) official home page: https://www.data.jma.go.jp), with a mean monthly temperature in Osaka 1.63 °C higher than the 11 year (July 2000–2010) mean. These elevated temperatures resulted in the highest on record hospitalisations (54,220) and heat stroke deaths (133) (Ministry of Internal Affairs and Communications, Japan 2018). Heat waves are expected to become more common and more intense with greenhouse gas (GHG)–induced global warming (e.g. IPCC 2013), exacerbated in cities by the urban heat island effect (e.g. IPCC 2014). Already 30% of the world’s population are exposed to deadly heat thresholds on at least 20 days per year, and this may increase to ∼74% by 2100 if GHG emissions increase (Mora et al 2017)
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