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sayThe “high temperature heat wave” seems to be just an adjective expressing heat, but it is just a few degrees hotter and a few days hotter. In fact, it is a “silent killer”, which causes a lot of casualties every year and is one of the most dangerous natural disasters.
World Health Organization (WHO) data shows that from 2000 to 2016, the number of people affected by heat waves increased by approximately 125 million people. In addition, the number of casualties caused by high-temperature heat waves is also growing much faster than all other extreme weather events (such as freezing, drought, floods and storms)[ 1].
The number of casualties caused by various types of meteorological disasters and their growth rate during 1991-2000 (blue) and 2001-2010 (purple)| Report on “Global Climate 2001-2010, Ten Years of Extreme Climate Events”
However, despite the high temperature and heat wave impact on life and health, it has not attracted enough attention. There are many and complicated reasons.
Lack of unified definitions and health assessment standards
At present, there is a lack of a unified definition of high temperature heat waves in the world, and various countries and regions are free to choose according to the local climate environment[3]< /span>.
For example, the World Meteorological Organization recommends that high-temperature heat waves be defined as weather processes with a daily maximum temperature above 32°C and lasting more than 3 days. Chinese MeteorologyThe bureau stipulates that the weather process in which the daily maximum temperature exceeds 35°C for more than 3 consecutive days is called a heat wave. Hong Kong, China, does not have the concept of heat waves. When the Hong Kong Observatory issues local hot weather warnings, it will use two custom indicators: hot days (the highest daily temperature ≥ 33℃) and hot night (the lowest daily temperature ≥28℃).
Because there is currently no uniform definition of high temperature heat waves in the world, there is no unified standard to measure the impact of high temperature heat waves on human health. Different evaluation systems in different regions have different evaluation errors, and there may even be a systematic underestimation [3-4].
Humidity: an important factor that is overlooked
Although most meteorological departments use temperature to define high-temperature heat waves, “humidity” is also an important factor affecting human perception. Different humidity makes high temperature heat waves can be divided into dry heat type and sultry type high temperature[5].
For example, Urumqi, located in a temperate semi-arid climate zone, and Guangzhou, located in a subtropical climate zone, are also at 32°C. The former has a relative humidity of only 30%, while the latter can approach 80%. The corresponding human experience is very different of. This is why some northerners have only discovered in the south that the same temperature is hot and unbearable, as if they were in a sauna. So sultry high temperature is also dubbed “Sauna days”.
Under the dual influence of climate change and urbanization, in recent years, northern cities such as Beijing and Xi’an have also begun to experience high-temperature and high-humidity “sauna days.”
So, in order to more comprehensively evaluate the high temperature heat wave, the national meteorological departments of the United States, Germany, Canada and other countries will build a comprehensive human “heat index” based on the three meteorological factors of temperature, wind speed and relative humidity, and release high temperature. Alert [6].
High temperature heat wave warning issued by the National Weather Service on July 18, 2019 | National Weather Service
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Hot night in the city: not yet alert
Everyone often thinks that the ambient temperature will naturally decrease after sunset, but in fact, there is also a “hot night” phenomenon caused by the urban heat island effect in the city-high-rise buildings in the city will absorb heat during the day, because Their specific heat capacity (indicating the ability of objects to absorb heat or dissipate heat) is high and heat dissipation is slow, so the duration of high temperature in the city at night It will be longer and the temperature will drop slowly.
According to the latest findings of the Hong Kong research team, areas with strong urban heat island effects and poor ventilation have higher relative health risks[7]. And when continuous hot nights appear, it will exacerbate the risk of heat death [8-9]. The latest health data of the Hong Kong Hospital Authority also shows that under continuous hot nights, the night admission rate and the number of ambulances are increasing, which indirectly shows that the impact of hot nights on health should not be underestimated.
At the same time, it is worth noting that Different areas of high temperature distribution during the day and night in the city[10]. At present, in the early warning system of related high-temperature heat waves, various measures often only consider the daytime situation, and ignore the nighttime situation.
Hong Kong high temperature distribution area during the day (left) and night (right) | References [10]
At present, the public is generally not aware of hot nights. In the continuous hot nights caused by high temperature heat waves, many elderly people still do not turn on the air conditioners or electric fans at night, or even sleep without opening the windows. These are all possible. Causes heat stroke.
Heat waves have a delayed effect on health
The health problems caused by high temperature heat waves are often not as obvious as other meteorological disasters. Its impact on the human body is a cumulative process, especially for patients with chronic diseases such as hypertension and heart disease, there is a delay effect of 3 to 5 days or even longer.
For example, the high temperature heat wave in the summer of 2003, although the temperature in Paris, France has shown a downward trend after August 14, but the number of deaths did not immediately decrease, but continued after the high death toll on the 5th, until August 19 The number of days has fallen to the same level as in previous years.
The number of deaths and the average daily temperature of the high-temperature heat wave in Paris in the summer of 2003 | References[11]
On the one hand, such a delay effect makes it difficult to assess health effects, and on the other hand, it also makes the public insufficiently aware of the health risks of heat waves-thinking that if the temperature drops, there will be no health risks.
The heat wave will aggravate air pollution and indirectly damage health
Continuous high temperatures under heat waves and changes in cloud cover may exacerbate photochemical pollution in the atmosphere, especially increase photochemical oxidants, such as sulfur dioxide and ozone. Therefore, Continuous high temperature and windless weather can easily induce air pollution and exacerbate the threat to human health.
For example, on May 1st this year, Beijing experienced high temperatures above 30°C, and on the other hand, it exhibited a complex high pollution situation. The concentration of ozone and PM 2.5 exceeded the national air quality standard by 2 to 3 times.
At present, although the weather forecasting and air pollution forecasting services of various countries are gradually improved, the global high-temperature early warning system does not combine the two to conduct a comprehensive assessment and carry out a composite meteorological disaster warning.
In view of this, the World Meteorological Organization proposed in 2019 the latest comprehensive city service guide, hoping to strengthen weather forecasting, extreme meteorological disasters and air pollution warning, and comprehensive environmental health assessment [12].
Complex extreme weather events affect all aspects of society
In addition to air pollution, different meteorological conditions and meteorological forms caused by climate change, combined with high temperature heat waves, composite extreme meteorological events(Compound Extremes) for energy, transportation, construction,Various aspects of social life such as agriculture and tourism have caused varying degrees of impact [13].
For example, in May 2018, there have been 16 consecutive days of high temperature heat waves in Hong Kong. At the same time, due to the lack of rain for a long time, the ponds have dried up and bottomed out, directly threatening the supply of drinking water.
The pond is dry and bottomed out | Wikimedia Commons, Hydrosami / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)< br>
In July 2019, the continuous high temperature heat wave raised the temperature in Europe to 40°C. Due to the radiant heat also soaring, trains in many places in the UK and France were forced to delay due to concerns about rail deformation and damage to railway cables. Or cancel [14].
In September 2019, due to the continued high temperature and dryness, Australia has erupted for 5 months and a protracted wildfire. The fire burned an area of 170,000 square kilometers, resulting in the death of more than 1 billion animals and 34 deaths. Over the past 20 years, such large-scale wildfires have erupted more and more frequently in Australia [15].
Due to continued drying, wildfires broke out in Australia for 5 consecutive months | 80 trading 24 / CC BY-SA (https://creativecommons.org/ licenses/by-sa/3.0)
At present, high temperature heat waves have brought many profound impacts to the human world, and the Intergovernmental Panel on Climate Change (IPCC) predicts that,< strong>In the future, high temperature heat waves will continue to wreak havoc, and the frequency will become higher and higher, and the intensity will become stronger and stronger [16] . We must face the existence of high temperature and heat waves, and be prepared to live in a world where the climate is getting hotter and more extreme.
References:
[1] WMO. (2020) Climate Change and Human Health: High Temperature and Health: Public Health Recommendations, World Meteorological Organization (WMO), Geneva, Switzerland; http:// origin.who.int/globalchange/publications/heat-and-health/zh/
[2] Ma W, Zeng W, Zhou M, et al. (2015). The short-term effect of heat waves on mortality and its modifiers in China: An analysis from 66 communities. Environ Int, 2015, 75: 103-109. DOI:10.1016/j.envint.2014.11.004
[3] WMO, & WHO. (2015). Heatwaves and Health: Guidance on Warning System Development, WMO-No. 1142. WMO, WHO. http://www.who.int/globalchange/publications/heatwaves -health-guidance/en/
[4] Huang Cunrui, He Yiling, Ma Rui, Su Yanan, (2018) The health effects of high temperature heat waves: from impact assessment to coping strategies, Journal of Shandong University (Medical Edition) Vol. 56 Issue (8): 14-20. DOI: 10.6040/j.issn.1671-7554.0.2018.160
[5] Weather Network (2019) Illustrated Weather, Meteorology Beijing Column, 2019, Issue 7, http://www.weather.com.cn/life/2019/ 05/3193515.shtml
[6] Li Wenqin (2011). High temperature science five: What is a high temperature heat wave? Meteorological Science (2011) http://www.cma.gov.cn/2011qxfw/2011qqxkp/2011qkpdt/201110/t20111026_124192.html
[7] Goggins, WB, Chan, EYY, Ng, E., Ren, C., et al. (2012). Effect Modification of the Association between Short-term Meteorological Factors and Mortality by Urban Heat Islands in Hong Kong. PLoS ONE, 7(6), 1-6. doi: doi:10.1371/journal.pone.0038551
[8] Wang, D., Lau, KK-L., Ren, C., Goggins, WB, III, et al. (2019). The impact of extremely hot weather events on all-cause mortality in a highly urbanized and densely populated subtropical city: A 10-year time-series study (2006–2015). Science of The Total Environment, 690, 923-931. doi: https://doi.org/10.1016/j.scitotenv.2019.07.039< /span>
[9] Liu, J., Hansen, A., Varghese, B., Liu, Z., et al. (2020). Cause-specific mortality attributable to cold and hot ambient temperatures in Hong Kong: a time-series study, 2006–2016. Sustainable Cities and Society, 57, 102131. doi: https://doi.org/10.1016/j.scs.2020.102131
[10] Shi, Y., Ren, C., Cai, M., Lau, KK-L., et al. (2019). Assessing spatial variability of extreme hot weather conditions in Hong Kong: A land use regression approach. Environmental Research, 171, 403-415. doi: https://doi.org/10.1016/j.envres.2019.01.041
[11] Vandentorren, S. and P. Empereur-Bissonnet, 2005: Health impact of the 2003 heat-wave in France. Extreme Weather Events and Public Health Responses, W. Kirch, B. Menne and R. Bertollini, Eds., Springer , 81-88.
[12] WMO, (2018), Guide for Urban Integrated Hydro-meteorological, Climate and Environmental Services, Vol. 1: Concepts and Methodology, World Meteorological Organization (WMO), Geneva;
[13]IPCC (2018). Managing the Risks of Extreme Events and Disasters to Advance, Climate Change Adaptation, Special Report of the Intergovernmental Panel on Climate Change (IPCC), https ://www.ipcc.ch/site/assets/uploads/2018/03/SREX_Full_Report-1.pdf
[14] Economic Reference News (2019) Heat wave continues Extremely high temperature “scorching” European economy, 2019-07-30,
[15] Chris Dickman (2020) More than one billion animals killed in Australian bushfires, 8 January 2020, https://www.sydney.edu.au/news-opinion/news/2020/01/08/australian-bushfires-more-than-one-billion-animals-impacted.html
[16] IPCC (2019). SPECIAL REPORT: GLOBAL WARMING OF 1.5 ºC, the Intergovernmental Panel on Climate Change (IPCC), https://www.ipcc.ch/ sr15/chapter/chapter-3/
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