I don’t know if you have noticed that every year someone says this year is the hottest year.
This year is no exception. Since the beginning of summer, all parts of the country have entered a continuous high temperature mode of “steaming above and baking below”. 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 Niña), high temperatures in the south will be particularly significant. In 2023 (El Niño), six high temperature heat waves will occur successively in North China, the Huanghuai region and other places.
2024 is the year after El Niño and also the transition year of the ENSO cycle. La Niña 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, the first regional continuous high temperature process occurred in North China and the Huanghuai area, 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℃, 1.2℃ higher than the same period of previous years, the highest since 1961.
The national average precipitation was 243.9 mm, 17% higher than the same period last year and the third highest in the same period in history.
The high temperature areas across the country mainly appeared in most parts of Xinjiang, between southern North China and the Huanghuai region, 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 values.
This year, the first high temperature process in North China and the Huanghuai region occurred 4.7 days earlier than usual and lasted for a total of 9 days.
The number of days with high temperatures in southeastern Hebei, western Shandong, eastern Henan, and northern Anhui is more than 5 days.
The extreme maximum temperature generally reached 38℃~40℃ in most parts of the Huanghuai region, southern Hebei and southern Shanxi, and exceeded 40℃ in southeastern Hebei, northwestern Shandong, central Henan and other places.
The area affected by high temperatures of 35°C and above in eight provinces and cities including Beijing, Tianjin, Hebei, Shanxi, Shandong, Henan, Anhui and Jiangsu is about 754,000 square kilometers, affecting a population of about 370 million people. Among them, the area with temperatures of 40°C and above reaches 166,000 square kilometers. There are 225 national meteorological stations with daily maximum temperatures exceeding 40°C, with the highest reaching 43.4°C in Wen County, Henan Province 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 (with 1 station exceeding 43°C), and 228 stations (accounting for 32.6%) exceeded 40°C.
In 2023, from May 28 to early July, six high-temperature heat waves occurred in North China, Huanghuai and other places, with 17 stations exceeding 42°C, 4 stations exceeding 43°C (the strongest was 43.7°C in Pingshan, Hebei), and 165 stations exceeding 40°C (accounting for 23.6%).
In the past 10 years (2014-2023), there have been ten 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 indicators of extremeness, the high temperature process from June 18 to 26, 2022 is the most extreme, followed by the high temperature process from June 21 to July 4, 2023.
Regional high temperature process in North China and Huanghuai during the first half of the year (2014-2023)
Which year was the hottest?
In recent years, large-scale heat wave events in my country have shown an increasing trend. As global warming intensifies, high temperature weather in my country 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 high temperature weather in the national region is being advanced by 2.5 days per decade.
From 1981 to 1990, the earliest high temperature weather process occurred on average on June 24, while from 2011 to 2020 it was advanced to June 7; the first regional high temperature process of the year occurred on May 28, 2023, 16 days earlier than usual.
The frequency of high temperature processes in the country has shown an increasing trend, with an average of 3.3 times per year from 1981 to 1990, increasing to an average of 4.1 times per year from 2011 to 2020.
The cumulative number of days with high temperature processes across the country has shown a significant increasing trend, increasing by 4.8 days every decade on average (Figure 1).
At the same time, the average impact range continues to expand, with an average of 258 stations affected during 1981-1990 and an average of 328 stations affected during 2011-2020.
The average intensity of regional high temperature processes increases 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
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, the water vapor transport is weak, and the main high temperature is dry heat. The temperature is high and the humidity is low, and continuous high temperature weather is prone to occur.
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.
Between 1981 and 2000, the average number of high-temperature days in Beijing-Tianjin-Hebei from June 1 to July 4 was 4.8 days, but during the same period from 2001 to 2023, the number of high-temperature days increased to 6.3 days, an increase of 32% over the previous period.
In the future, as global warming intensifies, my country's risk of extreme high temperatures will further increase, with more frequent, stronger, longer-lasting and wider-ranging heat wave events.
Global warming and the El Niño event are important climate backgrounds that cause a series of extreme high temperatures in my country.
Against the backdrop of global warming, average temperatures are rising and hot weather is 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 and intensification of 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 lagged effects will continue and there is a high probability that it will turn into a La Niña event in the summer of 2024.
El Niño/La Niña events affect the global atmospheric circulation through ocean-air interactions and lead to abnormal climate in various parts of the world, including my country.
The periodic atmospheric circulation anomaly is the direct cause of the regional high temperature weather.
The high temperatures in eastern my country are mainly affected by the subtropical high pressure in the western Pacific and the warm high pressure in the westerly belt. In areas controlled by warm high pressure, downward airflow prevails, the sky is clear and cloudless, it is not easy for clouds to form and rain, the solar radiation is strong, and the near-ground heating is strong. Under the conditions of an abnormally strong and stable high pressure system, it is very easy to form continuous high temperature weather.