◎Our reporter Fu Lili
A few days ago, according to media reports, the National Disaster Reduction Committee Office and the Emergency Management Department released the national natural disaster risk situation to the public, showing that the drought in the middle and lower reaches of the Yangtze River will continue or develop.
Why is this drought so ferocious, how long will it last, and how should we respond scientifically?
"According to the annual distribution of precipitation and the analysis of the characteristics of historical droughts and droughts in the region, it is preliminarily judged that the drought in Hunan, Jiangxi and other places in the middle and lower reaches of the Yangtze River will continue until March next year. Urban water supply is safe." On November 7, Lu Juan, director of the Flood Control, Drought and Disaster Reduction Center of the China Academy of Water Resources and Hydropower Science, said in an exclusive interview with a reporter from Science and Technology Daily.
Atmospheric circulation continues to be abnormal in some areas and even "empty plums"
"The large-scale drought this year is mainly caused by the continuous abnormality of atmospheric circulation." Lu Juan introduced that in the Yangtze River Basin, the subtropical high is an important weather system that affects its droughts and floods.
The inner area of the subtropical high is controlled by strong downdraft and tends to be sunny and less rainy, while the northern edge of the subtropical high is prone to strong precipitation as the place where the cold and warm currents meet.
Lv Juan said that usually, from early June to mid-July each year is the "Meiyu" season in the middle and lower reaches of the Yangtze River, but in June this year, due to the suppression of the "westerly trough" in the northeast, the western Pacific subtropical high was delayed northward, and its northern The edge is stable on the coast of South China, causing the plum rain that should have fallen in the middle and lower reaches of the Yangtze River to fall to South China, and even "empty plums" appear in some areas.
In July and August, the subtropical high in the western Pacific rapidly moved northward and extended westward. At the same time, the continental subtropical high abnormally located over the Arabian Peninsula to Iran extended eastward and northward. The upper, middle and lower reaches of the Yangtze River Basin have high temperature, fine heat and little rain.
Entering September, the autumn rains in Western my country quickly eased the drought in the Sichuan and Chongqing regions. Affected by the western Pacific typhoon, most of the water vapor in southern China was taken away. There was still not much effective precipitation in the middle and lower reaches of the Yangtze River, and the drought continued to develop.
"This year's drought in the Yangtze River Basin started in mid-to-late June, and it has been more than 4 months now. In addition to the autumn and winter seasons with less rain, the situation of continuous drought in summer, autumn and winter has basically taken shape." Lv Juan believes.
Drought in the main flood season in the Yangtze River Basin is not uncommon
In people's impressions, the Yangtze River Basin is relatively abundant in water resources, so this year's continuous high temperature and drought have led to the phenomenon of anti-drying in the flood season, which has attracted much attention.
"Actually, it is not uncommon for the Yangtze River Basin to encounter droughts during the main flood season. The Yangtze River Basin is a typical drought-prone area in my country, and regional droughts of varying degrees occur basically every year." Lu Juan said.
The data shows that since 2000 alone, several summer droughts have occurred in the Yangtze River Basin, among which the more typical ones are 2006, 2013, and 2019.
But Lv Juan also said that this year's drought should also show some characteristics that are different from those in the past.
For example, drought affects a larger spatial range, covering the entire upper, middle and lower reaches of the Yangtze River, which also brings certain difficulties to the regulation of water volume in the basin; the drought starts early and lasts longer; the severity of the drought is severe, and the middle and lower reaches of the Yangtze River The water inflow from the measured stations such as Hankou, Datong, and Jiujiang reached the lowest level in the same period since the measured record.
The water level of the main stream of the Yangtze River, Dongting Lake and Poyang Lake was 5.4-7.2 meters lower than the same period of the previous year, which was the lowest in the same period since the actual measurement record.
Then there is the wider impact.
In the past, drought generally affected agricultural production, drinking water for rural people and livestock, and urban water supply. This year, the drought has extended to many aspects such as shipping, energy, and forest fire safety.
"What is urgently needed is whether the existing water storage capacity of rivers, lakes and reservoirs can meet the water demand before the flood season next year, and the pressure on water security for industrial and agricultural production and residents' domestic life in the river basin has increased sharply, especially in some areas. Difficulties and challenges." Lu Juan emphasized.
Drought brings many thoughts and inspirations
In 2022, the drought in the Yangtze River Basin will have many adverse effects on life, production and ecology, and it has also caused people to think and enlighten a lot.
How should science respond in the future?
Lv Juan suggested that for government departments, it is necessary to focus on how to strengthen the response measures during the drought period and improve the emergency response capacity of drought resistance.
It is necessary to change the past practice of drilling wells, pulling water, and supplying water for drought relief in the past. During the drought period, the water volume of various water conservancy projects and regional water resources allocation projects between the left and right banks of the river basin, the main and tributaries, and the upstream and downstream of the river basin shall be jointly dispatched; Especially in areas where large and medium-sized water conservancy projects are difficult to cover and where drought-resistant infrastructure is weak, a number of small-scale reservoir projects, emergency drought-relief wells, and water diversion projects should be built according to local conditions, so as to improve the supply capacity of emergency backup water sources.
For scientific researchers, it is necessary to consider how to promote drought risk management and realize the integrated management of normal and emergency states.
It is necessary to break through the technical bottleneck of the whole chain of drought "monitoring → forecasting → early warning → rehearsal → planning", and to understand the problems of "where is the drought", "how much is the drought", "how long is the drought" and "how to do it", in order to realize the digitalization of drought disaster scenarios and intelligentization Simulation and precise decision-making.
"For the public, it is necessary to consider how to save and protect water, start from oneself, and protect the natural and ecological environment like protecting eyes." Lu Juan said.