It's rude to be hotter! Is it really normal to be so hot this summer?

I don't know if you have noticed that every year, some people say that this year is the hottest year. This year is no exception. Since the beginning of summer, the country has entered a continuous high temperature mode of "steaming up and baking down". Whether commuting to get off work or traveling, many people have to endure the "scorching" of the sun, which is unbearable.

How hot is this year?

As global warming intensifies, global heat waves and their complex meteorological disasters become more prominent. Combined with the ENSO events in the equatorial central and eastern Pacific, extreme weather becomes more frequent, more intense, and has a wider impact. At the same time, with the transition from El Niño to La Niña, the interannual characteristics become more complex.

In 2022 (La Nina), the high temperature in the south was particularly significant. In 2023 (El Nino), six high temperature processes occurred in North China, Huanghuai and other places. 2024 is the year after El Nino and the transition year of the ENSO cycle. La Nina will appear in late summer and early autumn, and high temperatures in North China, Huanghuai and other places will show new characteristics. From June 8 to 16, North China and Huanghuai experienced the first regional continuous high temperature process, which was characterized by early occurrence, wide range and strong extremes.

From April to June 2024, my country's weather and climate were abnormal, with high temperatures, heavy precipitation, and frequent extreme weather. The national average temperature was 17.3°C, 1.2°C higher than the same period of previous years, the highest value since 1961. The national average precipitation was 243.9 mm, 17% higher than the same period of previous years, the third highest in history.

The high temperature areas in the country mainly appeared in most parts of Xinjiang, the southern part of North China and the Huanghuai area, Hainan and parts of the southwest region. From June 8 to 16, a total of 168 national meteorological stations reached or exceeded the extreme high temperature threshold, of which 20 stations reached or exceeded the historical extreme value.

This year, the first high temperature process in North China and Huanghuai was 4.7 days earlier than usual and lasted for 9 days. The number of high temperature days in southeastern Hebei, western Shandong, eastern Henan, and northern Anhui was more than 5 days. The extreme maximum temperature generally reached 38℃~40℃ in most parts of Huanghuai, southern Hebei, and southern Shanxi, and exceeded 40℃ in southeastern Hebei, northwestern Shandong, and central Henan. The high temperature of 35℃ and above in 8 provinces and cities in Beijing, Tianjin, Hebei, Shanxi, Shandong, Henan, Anhui, and Jiangsu affected an area of ​​about 754,000 square kilometers, affecting a population of about 370 million people, of which the range of 40℃ and above reached 166,000 square kilometers. There were 225 national meteorological stations with daily maximum temperatures exceeding 40℃, with the highest reaching 43.4℃ in Wen County, Henan on June 13.

In terms of the intensity of the daily maximum temperature, from April 1 to July 7, a total of 26 stations in Beijing, Tianjin, Hebei, Shanxi, Shandong, Henan, Anhui and Jiangsu exceeded 42°C (one station exceeded 43°C), and 228 stations exceeded 40°C (accounting for 32.6%). In 2023, from May 28 to early July in North China, Huanghuai and other places, there were 6 high temperature heat waves, 17 stations exceeded 42°C, and 4 stations exceeded 43°C (the strongest was 43.7°C in Pingshan, Hebei), and 165 stations exceeded 40°C (accounting for 23.6%).

In the past 10 years (2014-2023), there have been 10 regional high temperature processes in North China and the Huanghuai region (see the attached table), and regional high temperature processes are prone to occur in June. Judging from the comprehensive extreme index, the high temperature process from June 18 to 26, 2022 is the most extreme, and the high temperature process from June 21 to July 4, 2023 is the second most extreme.

Appendix: High temperature events in North China and Huanghuai regions during the first half of the year

(2014-2023)

Which year was the hottest?

In recent years, large-scale heat wave events in China have shown an increasing trend. As global warming intensifies, high temperature weather in China in recent years has shown the characteristics of earlier first-start date, increased frequency, more cumulative days, wider impact range, and stronger comprehensive intensity.

The date of the first occurrence of regional high temperature weather processes in the country is advanced at a rate of 2.5 days per decade. From 1981 to 1990, the earliest high temperature weather process occurred on average on June 24, and from 2011 to 2020 it was advanced to June 7; the first regional high temperature process of the year will occur on May 28, 2023, 16 days earlier than usual. The frequency of regional high temperature processes in the country is increasing, with an average of 3.3 times per year from 1981 to 1990, and an average of 4.1 times per year from 2011 to 2020.

The cumulative number of days with high temperature processes in the country has shown a significant increase, with an average increase of 4.8 days per decade (Figure 1). At the same time, the average impact range has continued to expand, with an average impact of 258 stations from 1981 to 1990 and an average impact of 328 stations from 2011 to 2020. The average intensity of regional high temperature processes has increased at a rate of 6.2% per decade (relative to the average intensity from 1991 to 2020).

Figure 1961-2023 Cumulative number of days of high temperature processes in the whole country

The root causes of extreme heat events

The period from mid-to-late June to early July is usually the period when high temperatures are most concentrated in North China. At this time, the rainy season in North China has not yet begun, and the water vapor transport is weak. The dry heat type is the main type of high temperature, with high temperature and low humidity, which is prone to continuous high temperature weather. The main reasons are the stable control of the continental high pressure system; the synergistic effect of warm ocean water in key areas and the impact of human activities such as global warming and urbanization.

Since the 1950s, most regions of the world have observed an increase in the frequency and intensity of extreme high temperatures. my country has also experienced rapid warming, with extreme high temperatures intensifying, increasing in number, and lasting longer. In particular, the urban effect has exacerbated the intensity and duration of high temperatures. Human activities have had a discernible impact on these observed long-term changes.

From 1981 to 2000, the average number of high-temperature days in Beijing, Tianjin and Hebei from June 1 to July 4 was 4.8 days, but from 2001 to 2023, the number of high-temperature days increased to 6.3 days, a 32% increase over the previous period. In the future, as global warming intensifies, my country's risk of extreme high temperatures will further increase, with more and stronger high-temperature heat wave events that last longer and cover a wider range.

Global warming and El Niño events are important climate backgrounds for a series of extreme high temperatures in my country. Against the backdrop of global warming, average temperatures are rising and high temperatures are becoming more frequent. Since the mid-20th century, the extent of climate warming in my country has been significantly higher than the global average during the same period, and the increase in extreme high temperature events may have become the new normal. In addition, the El Niño event that began in May 2023 is now coming to an end, but its delayed impact will continue, and it is likely to turn into a La Niña event in the summer of 2024. El Niño/La Niña events affect global atmospheric circulation through sea-air interactions and lead to climate anomalies around the world, including my country.

The periodic atmospheric circulation anomaly is the direct cause of the regional high temperature weather. The high temperature in eastern my country is mainly affected by the subtropical high pressure in the western Pacific and the warm high pressure in the westerly belt. In the area controlled by the warm high pressure, the downward airflow prevails, the sky is clear and cloudless, it is not easy to form clouds and rain, the solar radiation is strong, and the near-ground heating is strong. Under the condition of abnormally strong and stable high pressure system, it is very easy to form persistent high temperature weather.

Author: Zhou Bing, Chief Climate Service Expert of National Climate Center

Editor: Wang Xue