Bracing for heat and humidity amidst new challenges in Tokyo

Abstract

After a year-long delay due to the COVID-19 pandemic, Tokyo 2020 is set to begin. Extreme heat in Tokyo and its impending challenges to athletes, volunteers, and spectators has been covered extensively in the literature in recent years [1,2]. Among these studies, few have drawn upon large-scale atmospheric patterns and intraurban climatology that help us answer the question “just how hot and humid could it be across and within the city?” compared to the climatological “normal” for Tokyo. Our recent article published in Temperature [3] focused on the multi-scalar heat challenges that will impact Tokyo’s weather at the Games––planetary atmospheric dynamics to intra-urban temperature variability––for the year 2020. However, with the unprecedented COVID-19 pandemic and one-year postponement of the Games, we would like to take this opportunity to provide an update on the atmospheric-ocean dynamics affecting Tokyo in summer 2021, and what these changes (as well as new COVID-precautions) mean for preparedness efforts for the athletes, coaches, clinicians, and volunteers (note: spectators are not allowed and are therefore not a concern). With a focus on the El Niño Southern Oscillation (ENSO), our 2020 paper assessed how summertime ENSO conditions affected Tokyo’s summertime wet bulb globe temperature (WBGT) using 35 years of data from 1981–2016. Depending on the atmospheric patterns within/over the Pacific Ocean, the summertime WBGT levels in Tokyo can vary by 3.95°C [3]. In late summer 2020, neutral ENSO conditions were present; last summer was warmer than average by +0.27°C across Japan according to the Japan Meteorological Association (https://ds.data.jma.go.jp/tcc/tcc/ products/gwp/temp/jun_wld.html). These neutral conditions were followed by a negative phase La Niña throughout the boreal autumn and winter. The ENSO pattern shifted back to a neutral phase in summer 2021, which is favored to remain all summer in the northern hemisphere [4]. Based on our work, there was only one year (1986, Quartile 3) where La Niña preceded a neutral year. This quartile represents WBGT levels in the second-highest quartile, with an average daytime WBGT of 28.1°C (range: 29.7–28.2°C) [3]. Moreover, this occurred in a period (pre-1990s) when the ENSO teleconnections (ability to influence weather in other areas) differed. Thus, there is no climatological analogy from which to extrapolate a possible pattern. In this case, standard local climatology may be the best guide, particularly because neutral conditions cause temperatures, winds, and rainfall in the tropical Pacific region to be near their long-term averages. With respect to sea surface temperatures in the Tokyo region, these temperatures are expected to be 0.5–1.0°C (July–Sept) above normal based on the APEC climate center multi-model deterministic forecast (www.apcc21.org/main.do) (note: for the Tokyo area, average water temperatures are 25.7°C for August). Hence, water temperatures for water events should remain below the maximum allowable level of 31°C. Combining standard climatology and current model predictions, athletes, coaches, and officials are well-aware of the heat and humidity expected in Tokyo from the end of July through September 2021. For example, daily average maximum air temperatures of 31.1°C should be expected across the venues coinciding with high relative humidity of ~62–72% (and high dew point temperatures ranging from 22–24°C) [3]. Our 2020 work further showed that these ambient conditions are variable within metropolitan Tokyo depending on facility location, with added solar radiation leading to maximum WBGTs that are commonly over the “cancel activity” threshold of 32.3°C based on the American College of Sports Medicine. The average daily WBGT levels are expected to range from 25.7–29.1°C, with daily maximum values expected to reach 33–34°C midday [4]. Such extremes may be new exposures levels never experienced for TEMPERATURE 2021, VOL. 8, NO. 3, 206–208 https://doi.org/10.1080/23328940.2021.1960104