Detailed explanation of the chief forecaster of the National Climate Center

Why is the global rainstorm concentrated at 40 degrees north latitude

  Author: Our reporter Zhang Yaxiong and Yuan Yufei

  Since June, there have been heavy rains in many parts of the world (China, Germany, the United States, etc.). Why do heavy rains in the northern hemisphere usually occur near 40 degrees north latitude?

Is it possible that the intensity of global extreme precipitation events will increase in the future?

How to mitigate the impacts of climate change?

What should the public do?

The reporter interviewed Chen Lijuan, chief forecaster of the National Climate Center.

  Reporter: Since June, why the heavy rain in the northern hemisphere has been around 40 degrees north latitude, and which weather and climate system dominates the respective precipitation?

  Chen Lijuan: We know that there are a total of six wind belts on the earth's surface, three in each of the northern and southern hemispheres. They are symmetrical about the equator. They are the low-latitude trade wind belt, the prevailing westerly wind belt, and the polar easterly wind belt.

The prevailing westerly belt is mainly located in the mid-latitude area, also known as the "mid-latitude westerly belt". The main affected latitude ranges from 30 degrees to 60 degrees north and south latitudes, of which 40 degrees to 60 degrees north and south latitudes are the main affected areas.

The continental area corresponding to 40 degrees to 60 degrees in the northern hemisphere is relatively large and has a large population. The impact of abnormal weather and climate is large, and the degree of attention is also high.

  The circulation in the mid-latitude westerly zone varies greatly. Sometimes the zonal type is dominant, the circulation is relatively straight, the exchange of cooling and heating is not violent, and the weather and climate characteristics are stable; sometimes the meridional type is dominant, with large grooves and ridges. It can guide the violent convergence of the north-south cold and warm air flow, resulting in severe weather.

Since June of this year, the mid-latitude circulation in the northern hemisphere has staged a "prank" activity involving large troughs and ridges, as well as the synergy of the intensity and location of the subtropical high.

  According to the monitoring of the National Climate Center, from late June to early July, the large troughs and ridges in the westerly belt of the northern hemisphere have very clear activities, showing a four-wave pattern. Among them, there is a high-pressure ridge in northern Europe, eastern Russia, western North America, and northern Atlantic Ocean. In the center, affected by the high-pressure internal sinking airflow, the temperature in most of Europe, eastern Russia, and western North America was abnormally higher than usual, resulting in high temperature and heat waves.

On the other hand, the subtropical high system is stronger than usual, and it expands significantly to the north. It cooperates with the circulation of the westerly zone and further causes abnormal weather and climate.

  From late June to early July, the East Pacific Subtropical High and the North American Westerly High ridge combined together to form a very strong blocking high, exacerbating the extreme high temperatures in Canada and the northwestern United States.

In mid-July, the North American subtropical high expanded northward, leading low-latitude water vapor to the eastern United States, where it converged with cold air guided by the low-pressure trough east of the North American high-pressure ridge, resulting in heavy precipitation in the eastern United States.

  The heavy precipitation process in Europe was jointly affected by the Mediterranean cyclone activity and the continued strong ridge of high pressure in the westerly belt. Among them, the heavy precipitation process from July 13 to 15 which caused serious casualties in Germany and other places was mainly due to the northward movement of the cyclone system from the lower Mediterranean. , Transporting a large amount of warm and humid water vapor northward, and being blocked by the high pressure system over the northeastern Atlantic Ocean to northern Europe, forming a cut-off low pressure, the water vapor convergence is abnormally strong, and a process of heavy precipitation occurs.

  The "July 20" rainstorm and flood disasters in Henan, China were jointly affected by the West Pacific Subtropical High and typhoon activities: In mid-July, the West Pacific Subtropical High was stronger and northerly, and Henan was at the western edge of the subtropical high. Convective and unstable energy was sufficient, and tropical regions Typhoon activities have entered a period of frequent occurrence. Typhoon No. 6 "Fireworks" developed simultaneously in the Northwest Pacific and Typhoon No. 7 "Chapaca" in the South China Sea. This strengthened the transportation of water vapor from the Northwest Pacific, South China Sea and the Bay of Bengal, and provided heavy rainfall in Henan. A sufficient source of water vapor.

At the same time, the strong northerly West Pacific Subtropical High and the continental high pressure in Central Asia have made the atmospheric circulation situation relatively stable, further extending the duration of heavy rainfall in Henan and other places.

  Reporter: As the seasons go by, how will precipitation change?

  Chen Lijuan: With the passage of the seasons this year, the subtropical system will be seasonally weakened and southward. The water vapor transport conditions will correspondingly weaken, and the heavy precipitation in the westerly zone of the northern hemisphere will also seasonally weaken.

  Studies have shown that with the increase in global average surface temperature, extreme precipitation events in most land areas in mid-latitudes and humid tropical regions are likely to increase in intensity and frequency; precipitation between wet and dry regions and between wet and dry seasons The difference will increase.

  Reporter: Does global warming have a direct impact on this year's heavy rainfall and other heavy rainfall processes?

How should the relevant impact be reduced?

  Chen Lijuan: A large number of studies have confirmed that in the context of climate change, because the warming atmosphere can hold more water vapor before it is saturated, the risk of extreme heavy precipitation is greatly increased when the precipitation conditions are favorable.

  The contribution rate of global warming to this year's extreme heavy precipitation process needs further study, but global warming has increased the probability of extreme heavy precipitation, which is widely recognized.

  We have only one earth, and the atmosphere knows no borders. In the face of global warming, no country or government can be spared. The whole society needs to attach great importance to it, strengthen the ability to respond to climate change, and mitigate the impact.

  The first is to actively adapt to the climate and strengthen disaster risk management.

  Actively adapting to climate change and vigorously strengthening disaster risk management are important means to reduce climate risk and ensure climate security.

It is necessary to actively adapt to the impact of global warming on my country’s natural ecosystem and economic and social development, improve the ability to adapt to climate change, especially to respond to extreme weather and climate events, strengthen monitoring, early warning and prevention, and improve key areas such as agriculture, forestry, and water resources. And the level of adaptation to climate change in ecologically fragile areas.

  The second is to make scientific use of climate and rationally develop climate resources.

  Make full use of climate resources such as light, heat and water, develop the climate potential of agricultural production, rationally develop and utilize climate energy such as wind and solar energy, especially the overall planning of marine productivity development and offshore wind power; promote economic and industrial layout according to climate characteristics and laws Be scientific, and promote the harmonious development of man and nature, and the coordinated development of economy, society and resources and environment.

Incorporate climate resources into major systems such as resource and environmental ecological management and control, natural resource assets and liabilities, and explore the establishment of urban scale control and industrial adjustment systems based on climate carrying capacity assessment.