Bracing for heat and humidity amidst new challenges in Tokyo

This article refers to:

A multi-scalar climatological analysis in preparation for extreme heat at the Tokyo 2020 Olympic and Paralympic Games

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 some competitors. Moreover, our work found that solar radiation was a dominant factor in discomfort at the highest WBGT in Tokyo under neutral ENSO conditions [3]. Re-emphasizing these findings helps anticipate the conditions of international events with such long lead times to guide long-term preparedness efforts to mimic competition settings. Specifically for Tokyo, heat acclimation/acclimatization to high humidity conditions may also take longer [5], and thus utilizing outdoor conditions and/or indoor heat chambers can aid in the physiological adjustments. However, because of the dangers of humid heat compared to dry heat, and the risk of dehydration with the physiological heat adaptation of increased sweating, athletes must be prepared to invoke other beneficial actions in addition to acclimat(iza)tion. These may involve pre-game/pre-event cooling, per cooling, individualized nutrition plans, personal/sport-specific heat coping strategies, and extra attentiveness to (de)hydration and to supporting efficient evaporative cooling by using fans. These efforts are particularly important for the sports we found to be most at risk due to their event characteristics (i.e., intensity, duration) and mid-day occurrence of events (e.g., road cycling, tennis, wheelchair tennis, women’s soccer). Recent work [6] has further highlighted the concern for medical personnel working in hot conditions when wearing protective equipment, and thus should also be sure to adopt more appropriate precooling strategies, work-rest schedules, and clothing to minimize overheating. Further, as part of protecting athletes from COVID-19, traveling athletes will likely have minimal opportunity to re-start training in natural heat once entering Japan. While the recent Athlete Playbook (version 3, June 2021; https://gtimg.tokyo2020.org/image/upload/production/mlmqnsphtv47sw0ftwbl.pdf) indicates that athletes are only required to quarantine at their accommodation for the first three days after the day of arrival, these athletes will still likely face strict regulations that will prohibit them from freely partaking in outdoor activities. Given the fluid situation surrounding COVID-19 variants, current regulations may change at the time of athlete arrival, as this depends solely on the level of risk it may bring to the local community. Further, irrespective of the COVID-19 situation, the rainy season in Tokyo may extend until just before the opening ceremony, which could directly impact the effectiveness of outdoor heat acclimatization training sessions (for example, athletes could lose their physiological heat adaptations during quarantine, yet may be less of a concern for athletes testing negative for COVID-19 according to the Athlete Playbook). Hence, athletes who aim to achieve and/or maintain their heat tolerance will be faced with complexity in implementing strategies to optimize their health and performance once entering Japan [2]. Therefore, the need to prime these athletes to withstand heat stress in their home country or in training camps prior to Tokyo may be heightened more for Tokyo 2020 than previous summer games. In summary, weather forecasts, both short-term and long-lead using ENSO, can be an important aspect of athlete preparation. Such information can help athletes plan and appropriately acclimatize or acclimate to local conditions ahead of competition. The 2020 Tokyo Olympics held this year in the midst of the COVID-19 pandemic add an additional layer of uncertainty, making careful planning all the more essential for athlete performance and safety in the heat.