Spatial analysis of outdoor wet bulb globe temperature under RCP4.5 and RCP8.5 scenarios for 2041–2080 across a range of temperate to hot climates

Abstract

Wet bulb globe temperature (WBGT) is commonly used to assess human physical activity limits and risk exposure to heat-related injury. Using Australia as a case study location, rates of change in WBGT across a range of temperate to hot and dry to humid climates in response to selected projected climate scenarios were investigated. An established physics-based method for estimating WBGT using standard meteorological data was incorporated into a spatial modelling framework to map WBGT for a baseline period (1986–2005) for mid-summer daytime, mid-summer early morning and mid-winter daytime scenarios, under clear sky conditions and both light (0.5 ms−1) and moderate (3.0 ms−1) wind speeds at a nominal resolution of 0.05 decimal degrees. The resulting maps of WBGT revealed significant spatial variability in the range and pattern of increased WBGT across the three baseline scenarios in response to projected change under RCP4.5 and RCP8.5 for 2041–2060 and 2061–2080 generated by the ACCESS1.0 climate model. Moderate wind speed scenarios produced significantly cooler WBGTs than the equivalent low wind speed scenarios, reducing mean modelled summer daytime WBGT by 3.2 °C, summer morning WBGT by 0.8 °C, and winter daytime WBGT by 3.0 °C. Projected future summer daytime WBGT under unshaded clear atmospheric conditions with light wind speeds can be expected to exceed the range of the commonly used heat categorisation system used to inform recommended restrictions on physical activity and regularly exceed 35 °C in northern Australia's equatorial and tropical climates by mid-century under RCP4.5 and RCP8.5. Summer early morning WBGT and winter daytime WBGT were projected to reach heat categories that would result in recommended restrictions in physical activity continuously (across consecutive 24-h periods) in summer and intermittently (for at least part of the day) year-round by 2050 with more severe conditions by 2070 and/or under RCP8.5 scenarios. Investigations into physical activity limits beyond the current highest heat category and the efficacy of the employed methodology to estimate WBGT above 35 °C using standard meteorological data are required to prepare for the projected warmer climate.