For the past few days, my country has experienced continuous high temperature weather. At present, the high temperature event has lasted for more than a month, affecting more than 900 million people. According to the monitoring of the National Climate Center, in June this year, the global average temperature was about 0.4 °C higher than normal, the highest since 1979. High temperature and heat wave events occur frequently in the northern hemisphere in summer. So, what is the recent high temperature extreme in my country and the northern hemisphere? What is the reason for the persistent high temperature? Will the high temperature continue in the future?
According to the monitoring of the National Climate Center, since June this year (as of July 12), the average number of high temperature days in my country has been 5.3 days, which is 2.4 days more than the same period in normal years, the most in the same period in history since 1961. There are 10 to 20 high temperature days in southern Shaanxi, Henan, southern Hebei, central and western Shandong, Anhui, Jiangsu, Zhejiang, central and northern Hubei, Chongqing, central and southern Xinjiang, and western Inner Mongolia, among which eastern and southern Henan, Anhui More than 20 days in northern, northwestern Hubei and southeastern Xinjiang, Luohe (33 days), Yongcheng (31 days), Wugang (31 days), Wuyang (31 days), Shenqiu (31 days), Xiang City (30 days) and Huaxian, Shaanxi (31 days), as well as Xinjiang Shanshan (36 days), Naomao Lake (33 days) and other places have more than 30 high temperature days, and Xinjiang Turpan and Tuokexun have 42 days. Compared with the same period of the previous year, the number of high temperature days in the above-mentioned areas is generally 5 to 10 days longer, among which most of Henan, northern Hubei, southeastern Shaanxi, central and northern Anhui, southern Shandong, and northwestern Jiangsu have more than 10 days.
Since June 13, my country has experienced the first regional high temperature weather process this year, with a wide range, long duration, strong extremes and great impact. As of July 12, the high temperature event has lasted for 30 days, covering a land area of 5.021 million square kilometers and affecting more than 900 million people.
A total of 71 national meteorological stations across the country have the highest temperature exceeding historical extremes, among which Hebei Lingshou (44.2°C), Gaocheng (44.1°C), Zhengding (44.0°C) and Yunnan Yanjin (44.0°C) have a daily maximum temperature of 44°C above.
Affected by the high temperature weather, since June 13, the electricity load of seven provincial power grids including Hebei, Shandong, Henan, Shaanxi, Gansu, Ningxia, Xinjiang and the northwest power grid has reached a record high. Due to high temperature and low rainfall, soil moisture in eastern Zhejiang, western Henan, southern Shaanxi, southern Gansu, and northern Sichuan was deviated, and drought conditions continued or developed in some areas. Since July, many people in Zhejiang, Jiangsu, Sichuan and other places have been diagnosed with heat stroke, and there have been deaths.
Since the beginning of the 21st century, the typical years of large-scale sustained high temperature events in my country are 2003, 2013, and 2017. Overall, this year’s high temperature event started earlier than the above-mentioned three years, and the duration and number of historical extreme stations are currently less than these three years. Although the scope of influence and the highest temperature at a single station are not as good as those in 2017, they have exceeded those in 2003. and 2013.
According to the monitoring of the National Climate Center, in June this year, the global average temperature was about 0.4°C higher than normal, the highest since 1979, with more than 2°C higher in northern Russia and western Europe. The daily maximum temperature in Spain, France and Italy exceeded 40°C, and many cities in France, Spain, the United States and Japan set new high temperature records. The temperature in Tokyo, Japan exceeded 35 ℃ for 5 consecutive days; the high temperature warning in the central and eastern United States affected about 125 million people, more than one-third of the US population; the extreme heat in the German state of Brandenburg caused forest fires due to extreme high temperature exacerbating drought. Compared with the same period in history, this high temperature and heat wave event in Europe, East Asia, and North America at the same time period broke the historical extreme value, and the impact range is wide, but the degree of impact is not as high as that of the 2003 high temperature event.
Since the beginning of the 21st century, high temperature and heat waves in the northern hemisphere have become more frequent in summer. From June to August 2003, most of Europe experienced a high temperature and heat wave that was rare in the past decades and even hundreds of years. The temperature as high as 38°C to 45°C caused nearly 21,000 deaths, and nearly 15,000 in France alone. People died from the heat.
From June to July 2017, many countries in North America, Europe and Asia suffered from extreme high temperature weather. The daily maximum temperature in Phoenix in the western United States reached 47°C; forest fires were caused by persistent high temperature weather in Portugal, Spain and the Russian Far East; India and Pakistan also experienced persistent high temperature heat waves.
On June 10, 2019, a record-breaking high temperature heat wave occurred in the western United States. The local temperature in San Diego, California, reached as high as 45°C, breaking the local high temperature record; there were many forest fires in Northern California, and about 45 million people in the western United States were affected by the high temperature heat wave.
From July to September 2020, the southwestern U.S. was the hottest and driest period on record, with severe fires in California and western Oregon, destroying more than 8,500 buildings and 41 deaths; Aug. 16, death The temperature in the valley was as high as 54.4 °C; on September 6, the temperature in Woodland Mountain reached 49.4 °C, the highest temperature in history in the Los Angeles area.
From June to July 2021, there will be a wide range of persistent high temperature weather in North America. Among them, British Columbia, Canada, set a record for the highest temperature in the country for 3 consecutive days within a week, resulting in more than 700 deaths.
The sixth assessment report of the United Nations Intergovernmental Panel on Climate Change (IPCC) pointed out that in the last 50 years, global warming has occurred at an unprecedented rate since the past 2000 years, and the instability of the climate system has increased. United Nations Secretary-General Guterres called it “Red Alert for All Humanity”. Global warming is the climate background for the frequent occurrence of high temperature and heat waves in the northern hemisphere, and the abnormal atmospheric circulation is the direct cause of the frequent occurrence of high temperature and heat waves in many places around the world since June. Since June this year, over the subtropical regions of the northern hemisphere, the western Pacific subtropical high pressure belt, the Atlantic high pressure belt and the Iranian high pressure have all strengthened in stages, thus forming a large-scale global warm high pressure belt.
Under the control of the warm high-pressure zone, the prevailing downdraft is conducive to the warming of the ground. In addition, under the action of the large-scale high-pressure zone, the air is relatively dry, and it is not easy to form clouds, which also makes it easier for solar radiation to reach the ground, resulting in frequent high temperature occurrences , and the intensity is strong, resulting in sustained high temperature and heat wave events in many parts of the northern hemisphere.
Specifically in my country, the ongoing La Niña event has provided important climatic background conditions for the occurrence and development of high temperature in the south since June this year. In particular, the development of the mid-latitude warm high pressure belt has strengthened in July, resulting in a wide range of high temperature weather. According to statistical analysis, in the summer of the following year for most La Niña events, the western Pacific subtropical high (referred to as the subtropical high) tends to move northward. Since late June this year, the subtropical high has moved northward, especially after the typhoon “Siamba” moved northward in early July, the subtropical high has strengthened to the west, and the Iranian high has been extended to the east. Combined with the mid-latitude continental high, a stable formation has formed over my country. The warm high pressure belt, which in turn caused a wide range of high temperature weather. In addition, due to the water vapor carried by the subtropical high, the humidity in the central and eastern regions of my country is relatively high, making the body temperature higher.