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Tokyo 2020: The Heat Factor

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Christoph Szubski *
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The 2020 Summer Olympics will take place in the midst of Tokyo’s hot and humid summer period, possibly exposing athletes and visitors to the most challenging conditions ever observed in the modern history of the Olympic Games. By illustrating observational data, this SPORTIFY CITIES report unambiguously demonstrates that, with maximum perceived or feels like temperatures regularly exceeding 45°C, the sheer scale and scope of the heat factor could greatly weaken an athlete’s performance and increase the risk of heat stroke. Hence, this rather neglected climatological aspect could potentially become one of the key defining planning features of an pre-Olympics training preparation cycle for many athletes aspiring to compete at the 2020 Summer Olympic and Paralympic Games.

In all, the report attempts to assess the severity and probability levels of sweltering temperatures during the upcoming Olympic events in Tokyo. It eventually provides athletes, coaches and officials with a selection of suitable regions in the world that could ideally be chosen as training camp locations for heat acclimatization purposes.



Heat and Humidity in Tokyo


The 2020 Olympic Games in Tokyo will be held during the city’s summer period, the hottest and most humid time of the year. In climatology and meteorology Tokyo’s climate is typically classified as ‘humid subtropical’ (based on the regularly used Köppen climate classification system), which is not necessarily a suitable climate zone for holding outdoor sporting events. After all, it has been proven that non-acclimatized athletes tend to under-perform when exposed to extremely high temperatures and high humidity levels.

Given that a large proportion of potential Olympians are not accustomed to subtropical or tropical climate conditions (that is, they mostly reside and train in other climate zones), this report hopes to provide prospective 2020 Olympic athletes with practical knowledge of the temperature and humidity levels in Tokyo. Moreover, it also discusses the implementation of suitable heat acclimatization strategies into their pre-Olympics training and performance diagnostics cycles.

Standard climate diagrams of Tokyo imply that the city offers fairly acceptable ambient conditions for sporting performance, with mean high air temperatures of approximately 30°C being displayed during the peak summer period. By design, however, such climate diagrams only indicate the average values observed over long periods of time (usually over several decades), concealing the wide range in daily temperatures, humidity levels or rainfall. Thus standard diagrams will not provide athletes and coaches with meaningful information on the significance of implementing adequate acclimatization procedures into their pre-Olympic training cycles.

To begin with, athletes who intend to participate at the Tokyo 2020 Olympics are therefore advised to examine the day-by-day and hour-by-hour variation of meteorological raw data during exemplary peak summer periods in Tokyo; that is, the months of July and August are of particular importance to all athletes and coaches.

The graph below, for instance, illustrates the air temperatures and humidity levels monitored at four different times of a day, starting on 24 July and ending on 9 August 2015 – the same calendar days during which the 2020 Olympics will take place. As Tokyo is under a strong and stable influence of subtropical winds originating from the Pacific Ocean during its peak summer season, this graph reflects a plausible trend of air temperatures and humidity levels that could be expected during the 2020 Olympic Games period. The 8am and 8pm values, for instance, are crucial to athletes, as many qualification and elimination contests will be scheduled during morning hours, whereas the main competitions will by and large be carried out in the early and late evening hours. And as for the hundreds of thousands of event visitors who will spend much of their daytime outdoors, the information about temperature levels at 2pm is certainly critical.



Plausible humidity levels and air temperatures over the course of the 2020 Olympics (based on data recorded in 2015)


As demonstrated in the graph above, it is nothing unusual for the morning air temperatures to reach 30°C, while the relative humidity levels are still high, mostly fluctuating between 60 and 8o% (if no rain is reported). In the afternoon the maximum air temperatures – measured in the shade – exceed 35°C on regular basis. And on a typical sunny day in July and August the relative humidity levels in Tokyo remain fairly high, barely dropping below the 50% levels.

In the early evenings, the air temperatures typically drop below 30°C, while the humidity levels start rising rapidly again, reaching values of slightly above 70% during a typical evening with no reported rainfall. Athletes who will have to get up later at night in order to get ready for their events scheduled in the very early morning hours need to be aware of the fact that the night air temperatures barely drop below 27°C and that the humidity levels regularly remain above 80%. By and large, air temperatures and relative humidity levels during Tokyo’s peak summer period starkly resemble the 24-hour meteorological patterns observed in cities located within the tropical climate zone, such as Singapore – as demonstrated in the SPORTIFY CITIES Special Report on sporting and active lifestyle in Singapore (Chapter 12).

These observational data clearly demonstrate that both athletes and event visitors are likely to be exposed to challenging heat and humidity levels throughout their entire competition period. That is, athletes competing during the supposedly comfortable morning hours will, too, be exposed to challenging ambient conditions, given that air temperatures usually rise fairly quickly in Tokyo, reaching almost intolerable levels by 10am. (Given that the sun rises before 5am during Tokyo’s summer, its late morning air temperatures at 10am are comparably higher than in Singapore – the sun typically rises at around 7am in this tropical city in South-East Asia.)

On top of this, the intense solar ultraviolet radiation prevailing during Tokyo’s summer rapidly inflates the heat factor throughout the morning (this performance-affecting aspect of sun exposure is not reflected in the standard air temperature – which is measured by a thermometer located in the shade). The only time of relief appears to be in the early and late evenings; however, after sunset the rising humidity levels usually offset the slightly lower and more comfortable air temperatures.

Again, if non-acclimatized athletes get exposed to such high ambient temperatures and humidity levels, they generally experience a decline in sporting performance due to hyperthermia (and the risk of medical emergencies is increased, too). That is, failed thermoregulation leads to elevated core body temperature, which typically results in impaired cognitive functioning, reduced complex task levels and/or diminished response of the cardio-respiratory system.



‘Feels Like’ Temperatures


As outlined above, Tokyo’s high air temperatures during its summer period will most likely have a significant impact on athletes’ individual performances at the 2020 Olympics. In order to get more accurate information on how an athlete’s body will actually perceive this local heat factor during the upcoming Olympics, other meteorological aspects would need to be factored into the standard air temperatures. For instance, the assessment of the ‘feels like’ or ‘perceived’ temperature (also known as ‘apparent temperature’) would certainly be more telling, as this calculated value also takes into account the humidity levels and wind speed.

Due to the weighty influence of these two meteorological variables – i.e., humidity and wind speed – on tangible temperature levels, a recorded air temperature of 30°C, for example, can be perceived as 30°C in one part of the world, whereas elsewhere it feels more like 40°C. In other words, identical air temperatures recorded at various locations around the globe get perceived differently.

During Tokyo’s summer the ‘feels like’ or ‘perceived’ daytime temperatures regularly exceed the 45°C mark – occasionally, the extraordinary levels of 50°C are reached. Based on these measurable observations, many athletes competing at the 2020 Olympics will most likely face an extreme ambient environment. And the high ‘feels like’ morning temperatures of above 40°C indicate that even athletes participating in qualification and elimination contests (which are typically scheduled during morning hours) will also have to endure harsh meteorological conditions.

Besides, all prospective Olympic athletes should bear in mind that the effects of solar radiation are yet to be factored in. In the European Journal of Applied Physiology – an academic journal – Otani and his colleagues have recently demonstrated that, for instance, endurance exercise performance in a hot environment weakens progressively as solar radiation increases. According to the Australian Bureau of Meteorology, direct sun exposure in the middle of the day could add as much as 8°C to the ‘feels like’ temperatures – that is, on a clear sunny day in Tokyo the already extraordinarily high temperatures could potentially result in perceived temperature levels of almost 60°C (!).

Given such extreme heat conditions and periods of consecutive sunny days during Tokyo’s peak summer period, this information on solar radiation would also need to be taken into consideration before planning and constructing the key 2020 Olympic facilities. In particular, the artificial islands located in the Tokyo bay zone – many Olympic sporting venues and the Olympic village will be built around this key waterfront area – should be designed with vast parkland space consisting of large numbers of subtropical trees so as to provide the largely non-acclimatized event visitors with the much-needed shade and to reduce the extremely high heat levels around the large-scale sporting facilities (particularly, visitors with pre-existing heart conditions are at high risk).



Exemplary average maximum ‘feels like’ temperatures in selected cities observed during the cities’ hottest one-month period in 2015. Only the ‘feels like’ temperatures in Dubai, Singapore and Rio de Janeiro exceed the levels that may prevail during the 2020 Olympic Games in Tokyo.


To help athletes gain better understanding of the dimension of the heat factor facing them during the 2020 Olympics, it is worth matching Tokyo’s feels like temperatures with the observed levels in other cities around the world – as illustrated in the graph above. As most people understandably struggle to make sense of abstract meteorological numbers, such comparative figures can hopefully provide them with real-life reference points. It is, after all, reasonable to assume that peoples’ subjective perception of temperatures experienced in any of the selected cities could possibly enable them to better relate to these rather abstract values.

The graph below displays an exemplary range of maximum feels like temperatures of Summer Olympic Cities of the past four decades. For this comparison, meteorological data of all cities were compiled for any given period during which the specific Olympic Summer Games took place. By nature, temperatures and humidity levels – among other meteorological variables – fluctuate on year-to-year basis, with some geographic locations demonstrating larger variations than others. To minimize the risk of an outlier effect, feels like temperatures for nine consecutive years, from 2008 to 2016, were collected and averaged for this comparison.



Athletes competing at the 2020 Tokyo Olympics are likely to be exposed to the hottest perceived temperatures ever experienced during the modern Summer Olympic Games.


On the whole, the graph offers a fairly reliable picture of the meteorological conditions during recent Olympic Summer Games, with Tokyo displaying the highest feels like temperatures compared to previous Olympic Cities. Although the Games in Atlanta (1996), Athens (2004) and Beijing (2008) were, too, scheduled during the cities’ hot summer periods, their feels like temperatures are no match to the potentially extreme temperatures during the upcoming 2020 Olympics. In fact, no other host city of the Modern Olympic Games, dating back to 1896, demonstrates such challenging heat levels.

It is fair to say, of course, that the weather conditions during the 2020 Summer Olympics could be less harsh than those in 2014, 2015 and 2016, for instance: with average feels like temperatures ranging from 41 to 45°C in three consecutive years, these values are at the higher end of the monitored temperature scale (see graph above). And if a higher number of wet weather systems originating from the Pacific Ocean happen to influence Japan during the 2020 Olympic Games period, the feels like temperatures will possibly drop to as low as 35°C. Yet although this is the best-case scenario one could hope for, the occurrence of such subtropical wet weather systems, on the other hand, would certainly lead to even higher humidity levels.

The upcoming 2020 Paralympic Games in Tokyo will also be held during the summer period, starting on the 25th August and finishing on the 6th September. Yet thanks to the increasing number of wet and slightly cooling low-pressure systems passing through the region in August and September, local temperatures during the 2020 Paralympics are expected to be slightly lower compared to the 2020 Olympic Games levels. That said, the maximum feels like temperatures in Tokyo typically range between 30°C and 43.5°C during late August and early September (see graph below). Hence, the 2020 Paralympics in Tokyo could potentially become the hottest event in the history of the Paralympic Games. To complicate things further at the 2020 Paralympics, the greater likelihood of typhoon events during the late summer season could result in high volumes of rainfall and major interruptions to the schedule.



The graph ranks the five warmest host cities of the Summer Paralympic Games (based on temperatures recorded during a given Paralympics period). With an average maximum feels like temperature of 36°C Tokyo clearly tops this heat ranking.


Taken together, athletes planning to compete at the 2020 Olympics or Paralympics can not count on pure luck. And although this report does not claim to be able to predict the meteorological conditions during the 2020 Olympics, it highlights the potential risk of heat exposure for prospective athletes and visitors alike. To underline the importance of adequate training preparation and heat acclimatization procedures for the Olympic Games in Tokyo, one should therefore recall the 8th of August 2008; on this particular day the maximum feels like temperature observed in Tokyo reached staggering 55°C. In short, potential 2020 Olympics athletes should undertake the necessary climate acclimatization measures.



Acclimatization Measures for Olympic Athletes


In order to be able to perform at the highest possible levels at the 2020 Olympic Games in Tokyo, potential athletes will have to incorporate the heat factor into their pre-Olympics training cycles – that is, the systematic scheduling of hot and humid environments into their training cycles. Furthermore, personalised, time-dependent acclimatization progression will need to be assessed at least one year prior to the Olympics, while taking into account the differing physical requirements of the sports.

To be clear, adequate heat acclimatization procedures are crucial to improving the neuromuscular and metabolic capability of non-acclimatized athletes when performing under hot and humid conditions. In this way, the individual heat tolerance levels can be increased and the risk of sporting under-performance can be minimized thanks to higher efficiency of heat-regulating mechanisms of the body.

Surprisingly, however, among top athletes the implementation of heat acclimatization protocols is not as common as one would expect. According to a survey by Périard and his colleagues only 15% of professional track and field athletes participating at the 2015 World Athletics Championships in Beijing appeared to have incorporated heat-acclimatization training regimes into their preparation cycles in the lead to the championship (again, the heat and humidity levels at the upcoming 2020 Tokyo Olympics are expected to be significantly higher than in Beijing). Given that the large majority of all competing athletes at the World Athletics Championships in Beijing represented countries that are not located in subtropical/tropical climate zones, this high proportion of non-heat-acclimatized competitors (85% of all surveyed athletes) appears rather baffling for this professional sport.



Tokyo’s heat factor will most likely take a toll on athletes competing in outdoor events.


Regarding the suitability of heat acclimatization procedures, the use of generic acclimatization chambers is an acceptable option for athletes competing in individual endurance sports and wanting to get accustomed to heat and humidity conditions; yet their limited space makes them a highly inefficient and restrictive choice for larger national teams, game sports and sports-specific, multi-functional tasks. As a result, their role is largely limited to standardized training assessments on cycle-ergometers, treadmills or rowing machines.

Hence, spending longer periods of time in a naturally hot and humid ambient environment that is identical to the likely meteorological conditions during the 2020 Olympics looks set to become the more effective heat acclimatization procedure in a pre-Olympics training cycle. In this way, individual athletes as well as large teams could get accustomed to the challenging circumstances – that is, the naturally hot and humid environment – and, at the same time, execute sports-specific tasks for longer periods of time. During such acclimatization training camps of two to three weeks – this duration has been considered to be sufficient, according to a recent consensus article published in the academic British Journal of Sports Medicine – information on personalised acclimatization processes would frequently need to be gathered in high-performance laboratories (yet data collection must not be limited to physiological performance diagnostics), helping coaches to establish the most suitable acclimatization patterns for their athletes. In order to boost overall performance levels during such brief heat acclimatization training cycles, however, high-intensity and high-volume sports-specific training sessions should regularly be carried out in a more pleasant environment – that is, in air-conditioned gyms and sport halls.

One of the key challenges for national performance diagnostics analysts and coaches will also be to correctly interpret the latest research findings published in academic journals and to implement personalised acclimatization testing outcomes into their athletes’ real-life training and performance cycles (compared to other research topics on elite sports performance, however, there is still surprisingly little research available that examines the effects of heat acclimatization on sports-specific physiological adaptation processes). On the other hand, thanks to the evolution of wearable technology in the sporting industry, the application of novel, wearable devices that measure relevant thermal variables as well as physiological parameters will certainly become the tools of choice, enabling national teams and their performance diagnostics professionals to gather more personalized information in hot and humid natural environment.

In this regard, it also needs to be underlined that the performance of an athlete must not be confined solely to physiological parameters. To date, however, exercise physiologists have been dominating the research work on heat acclimatization and performance, largely focussing on assessing physiological parameters and applying aerobic, endurance testing protocols. That is, very little is known about the impact of high temperatures and humidity levels on non-endurance sporting tasks and other key components of an athlete’s overall performance. For instance, there appears to be barely any evidence-based information on the effects of hot and humid conditions on a number of relevant aspects of sporting performance, such as mood, irritability, intrinsic motivation, sleep quality, neuromuscular coordination, concentration capability or cognitive capacity – to name a few. And investigations on the adaptation patterns of these crucial factors during longer heat-acclimatization periods are absent, too. Given that research studies have yet to provide clear insights into the relationship between heat exposure and the above-mentioned fundamental elements of sporting performance, nobody should prematurely argue that brief, anaerobic and high-skill sporting tasks remain consistent and unaffected when non-acclimatized athletes are exposed to high temperatures and humidity levels during sporting events. To be clear, non-endurance athletes, too, should implement heat-acclimatization protocols into their pre-Olympics training cycles.

For many top-sporting nations, capital-intensive sports teams and national sports federations with limited budgets, however, the provision of the most efficient acclimatization options for their Olympic athletes will eventually become a logistic and financial issue. For one thing, in most countries with long sporting tradition subtropical climate conditions are absent. For another, if national sports organisations choose to invest into overseas trips for heat acclimatization and training purposes, adequate access to high-quality sporting infrastructure and provision of in-built high-performance diagnostics facilities will need to be guaranteed.

As for the prospective 2020 Olympians who live and train in locations within tropical climate zones, that is, the so-called tropical natives, such costly heat acclimatization trips can be largely avoided. After all, the all-year-round temperature and humidity levels in most parts of the world’s tropical regions typically reach identical or even higher levels that are likely to be experienced during the Tokyo 2020 Olympics period. There has been some speculation, however, that additional artificial heat exposure could perhaps result in enhanced tolerance to hot and humid conditions among athletes who are already naturally accustomed to hot and humid conditions. In this regard, it will be interesting to observe whether the exercise physiology & performance research community can establish such novel acclimatization protocols prior to the 2020 Olympics, potentially giving trained tropical natives substantial performance advantage over heat-acclimatized tropical non-natives. According to Jason KW Lee, an expert on this topic and the Head of the Human Performance Laboratory at DSO National Laboratories in Singapore, there is scope for acclimatization programs of greater exercise intensity or higher heat-humidity in trained tropical natives.



Acclimatization Suitability of Regions around the World


Japan, as the host nation of the 2020 Olympics, will surely be in an advantageous position in terms of providing their top athletes with great heat acclimatization options. The local climate will enable the country’s athletes to carry out some segments of their pre-Olympics training preparation under inhospitable ambient conditions, that is, hot and humid weather. After all, during the fairly long and stable summer period of two months much of the country’s southern and middle region is perfectly suited for training camps and large-scale acclimatization assessments.

Also, the top-tier sporting nation of China is in a formidable position. Many urban locations in the country’s south-eastern region – for instance, the Guangdong province – offer very high feels like temperatures and humidity levels for as long as 3 to 4 months, providing its national Olympic teams with extensive training and high-performance diagnostics options.

In South Korea, and in particular in the region along the Han River, suitable temperatures and humidity levels typically prevail for several weeks during the country’s summer season. That said, Tokyo’s levels of extremely high feels like temperatures can not be reached.

The USA Olympic team is in an enviable position, too; the areas around the cities of Houston and New Orleans demonstrate suitable feels like temperatures during the months of July and August. The provision of high class-sporting facilities in these regions is a further boon for its national teams.

Australia, another top-tier sporting nation, can also claim to have perfect acclimatization options in the northern region of Northern Territory and the north-eastern parts of Western Australia. Darwin, for instance, could serve as a training base throughout the long rain season, during which the feels like temperatures typically range between 40 and 55°C. However, it is not an ideal location choice for the pre-Olympics heat acclimatization period, as the most suitable conditions with high temperatures and humidity levels prevail solely between October and March (whereas the Tokyo 2020 Olympic Games will begin in July).

Brazil, the host country of the 2016 Olympics, too, is in an enviable position. Being largely located in tropical and subtropical climate zones, it has countless training and high-performance diagnostics sites to choose from.

By contrast, all European countries, including Russia, are less blessed with their climate zones. Although the southern regions of the continent show fairly high air temperatures during the European summer, they are, by and large, associated with low levels of humidity. And although the western and central parts of Europe usually experience a number of hot and humid summer days, these heat wave periods are far too short and too irregular to be incorporated into Olympic preparation cycles in any meaningful way. In Russia, only the city of Sochi, located at the Black Sea, reaches feels like temperatures of above 40°C. Yet its limited number of high temperature days, typically prevailing between the end of July and mid August, makes Sochi a rather unsuitable heat acclimatization location during the pre-Olympics period.

In all, it becomes evident that at the Tokyo 2020 Olympics the sporting nations located in non-sub-tropical climate zones as well as national teams with limited financial resources – and especially the mostly low-budget Paralympic national teams – could end up being in a disadvantageous position compared to the countries mentioned above. For the affected sporting teams it is therefore highly recommended to arrive two to three weeks ahead of the Games so as to at least enable their athletes to acclimatize to the local subtropical climate in a timely manner.

National Olympic Committees, coaches, high-performance diagnostics experts and Olympic athletes representing the better-off countries, that is, countries located within subtropical climate zones, will, on the other hand, need to strike a balance between regular performance development of their athletes and efficient acclimatization measures. Much of the pre-Olympics training preparation cycle will surely be carried out in more pleasant temperatures and humidity levels, assuring the maximization of an athlete’s performance. But simultaneously, personalized heat and humidity acclimatization periods consisting of various optimal durations will have to be implemented into training cycles without jeopardising the athletes’ overall performance evolution.

Regular acclimatization testing procedures should also include the personalised assessment of the most relevant sports-specific physical conditions, food and fluid intake requirements as well as the most suitable cooling options. Although this report does not discuss the effectiveness of conventional on-site strategies for reducing athletes’ core temperatures under hot and humid conditions, such as cooling, fluid intake or clothing, it needs to be pointed out that all prospective Olympians can, of course, adopt a series of measures to reduce the heat-related risk of performance decline during the 2020 sporting event. Devoted national coaches who feel comfortable applying scientific knowledge into practice should therefore be referred to some excellent scholarly work on this topic that has over the years been conducted by Samuel N Cheuvront (Natick, Massachusetts, USA), Jason KW Lee (Singapore) and Rob Duffield (Sydney, Australia).



Key Performance Factor


Preparations for the 2020 Olympics will undoubtedly pose challenges to all involved sporting team members, not least because heat-acclimatization procedures will need to be tailored specifically to the physical requirements of each sports. Yet if managed successfully, it could prove to be one of the defining features of individual performance during the most sweltering Olympic Games in modern history.



The majority of the 2020 Olympics competitions will take place on one of the artificial islands, such as Odaiba, located around the Tokyo Bay. The lack of trees and the proximity to water will aggravate the heat factor and increase humidity levels.


Again, this report aims to outline, illustrate and discuss the probable heat conditions during the Tokyo 2020 Olympics for mainly two reasons. For one thing, athletes should be provided with this crucial information a couple of years prior to the Games so that this knowledge and personalised acclimatization datasets can be incorporated into pre-Olympics training preparation cycles. For another, the event organisers will need to come up with a well-thought-out competition scheduling so as to reduce the levels of discomfort for both athletes and spectators. Likewise, the provision of large numbers of resting zones containing air-conditioning areas and sun protective features will most certainly have to become an essential element of the newly built sporting infrastructure.

This report does not intend to paint a bleak picture of the meteorological situation. Rather, it is an informative overview of the likely temperatures and humidity levels during the 2020 Olympics, which should be circulated among professional athletes, coaches, National Olympic Committees and event organisers. And yet, it is probably only a matter of time before national sports organisations and the international media start addressing this subject of heat exposure, which could potentially become one of the most-discussed topics ahead of the 2020 Summer Olympic Games.



This report was published in July 2016; it has been updated with additional data analyses.


For Reference Citations:
Szubski C.: Sweltering heat at the 2020 Olympics in Tokyo. Sportify Cities Report. 2016.






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