In the past few days, autumn rains have been rolling in western China, with occasional heavy precipitation and heavy rain. According to the monitoring of the meteorological department, this year's autumn rain in West China is 13 days earlier than usual. What are the characteristics of autumn rain in West China this year? What is the expected strength? In what areas may the autumn flood occur? On these issues, the reporter interviewed Wang Yongguang, chief of the Climate Prediction Office of the National Climate Center.
Guest: Wang Yongguang, Chief of the Climate Prediction Office, National Climate Center
Reporter: Cui Guohui, reporter of China Meteorological News, Wang Meiying, reporter of Xinhuanet Hao Duo
Reporter: How is the autumn rain in West China this year and what are its characteristics?
Wang Yongguang: According to the National Climate Center's West China Autumn Rain Monitoring Standards, the North and South Districts of the West China Autumn Rain Region have entered the Autumn Rain Period in 2019.
Among them, the southern area (including western Hubei, western Hunan, Chongqing, eastern Sichuan, northern Guizhou, and southern Shaanxi) entered the autumn rainy season on August 27, 13 days earlier than usual (September 9); the northern area (including Shaanxi) Most of the south, southern Ningxia and southern Gansu) entered the autumn rainy season on September 9th, one day later than usual (September 8th).
Although the autumn rain in the Southern District started early this year, there is an intermittent period of precipitation. From August 27 to September 17, the number of days when precipitation reached 50% of the stations was 13 days, and the average daily precipitation at the largest station appeared on September 8 at 16.45 millimeters.
The autumn rain in the North District has been more sustained so far. From September 9 to September 17, more than 60% of the stations in the North District experienced precipitation, and the average daily precipitation at the stations was generally stronger than that in the South District, with the maximum occurring on September 14 at 35.57 millimeters.
Autumn Rainfall in West China Changes from August 27 to September 17
In general, as of September 17, except in some parts of the eastern part of the western China autumn rainfall, precipitation was significantly lower than in the same period of the year, and most of the other regions were significantly higher, including central and southern Shaanxi, eastern Gansu, eastern Sichuan, northern Chongqing, Precipitation in northern Guizhou is 50% to 2 times higher, and local area is more than 2 times higher. Cumulative precipitation centers appear in eastern Sichuan, southern Shaanxi, and northern Chongqing. The cumulative rainfall in these areas has reached 200-400 mm. It is necessary to prevent geological disasters such as debris flows and landslides caused by continuous precipitation.
Map of Autumn Rainfall in West China from August 27 to September 17
Distribution of precipitation anomalies in West China from August 27 to September 17
Reporter: What are the climatic reasons for the early autumn rain in the Southern District and the slightly later in the Northern District this year?
Wang Yongguang: Since late August, the subtropical high in the western Pacific has been strong, and the western extension of the ridge point is significantly west, which is conducive to warm and humid air flowing northward along the periphery of the subtropical high to reach the autumn rain region; the negative anomaly over the altitude field is controlled over Lake Balkhash. Westerly and southerly of the area, the cold air on the west road is frequently active and intersects with the warm and humid airflow in the autumn rain area, creating favorable conditions for precipitation in the Yunguichuan area.
The maintenance of this anomalous circulation situation led to the continuous precipitation process in the southern part of the autumn rain region in western China in late August. The southern region entered the autumn rain period significantly earlier than usual, and the autumn rain in the northern region started almost one day later than usual.
Reporter: The autumn rain in western China is usually a light drizzle, but why sometimes there are short-term heavy rainfall and heavy rain, and even cause autumn floods? How is it this year?
Wang Yongguang: Although the amount of autumn rain in western China is less than that in summer, it lasts for a long time, and the precipitation is uneven, which is likely to cause autumn floods. During this year's southern autumn, there were short-term heavy precipitation and heavy rain events, and local heavy rain events appeared. There were two significant large-scale heavy precipitation processes, which were September 8-11 and September 13-14, respectively. .
Among them, from September 8th to 11th, the rainfall affected a wide range and had a strong intensity, with heavy rains in some areas and heavy rainstorms in some areas. Rainfall in eastern Sichuan, western Chongqing, central and western Guizhou, central and southern Shaanxi exceeded 50 mm, and the local area exceeded 100 mm. Cumulative precipitation over 6 stations including Guizhou Zhijin (234.6mm), Zhenfeng (224.5mm), Guanling (219.6mm), Zhenning (208.8mm), Xishui (207.2mm) and Sichuan Wangcang (220.1mm) exceeded 200 millimeters, and the coverage area of process precipitation above 50 millimeters is 420,000 square kilometers.
Affected by heavy rainfall, some rivers in Shaanxi, Sichuan, Chongqing, Guizhou, Gansu, Yunnan and other places have experienced rising water levels, flooded farmland, severe waterlogging in cities and towns, and suffered local landslides, landslides, and other disasters.
Since September 8, rainstorms have repeatedly occurred in the upper reaches of the Weihe and Hanjiang river basins, and the soil has become saturated. There have been significant flooding processes in the main and tributaries of the Weihe and Hanjiang rivers, and multiple tributaries have experienced alarming floods. It is necessary to closely guard against possible autumn floods.
Reporter: What is the trend of autumn rain intensity in West China in recent years? How strong is expected this year?
Wang Yongguang: In the 11 years since 2000, the comprehensive intensity index of the autumn rain in West China has been positive for 6 years, of which 5 is more than 0.5, which is a strong year; and the weak year with a negative anomaly below -0.5 is only 3 year. The comprehensive intensity index and total precipitation during the autumn rain period have increased slightly since 2000, but are not significant.
Comprehensive Rainfall Intensity Index of West China (from 2000 to 2018)
Autumn Rainfall in West China (2000-2018)
Since 2000, the autumn rain in West China has shown obvious interannual variability characteristics. The occurrence of strong and weak years has no obvious interdecadal characteristics. In the past three years, the intensity was weak in 2016, strong in 2017, and slightly weaker in 2018.
From the perspective of regional differences, in the past 11 years, there have been more strong years in the south and more weak years in the north.
It is expected that there will be more precipitation in the northern region of autumn rain in western China this year, and the rainfall will be 10% to 20% more than usual (136.5 mm). There will be more autumn rain in the Weishui River Basin and the upper reaches of Han River, and autumn floods may occur. Autumn rain in southwestern China is distributed "less in the northwest and more in the southeast", and the rainfall is close to normal (184.4 mm).
Reporter: What are the possible impacts of autumn rain in West China, and how to deal with it?
Wang Yongguang: September is the season for harvesting crops in western China. Overcast and rainy photos have adversely affected crop production. Mature autumn grains are prone to germination and mildew, and immature autumn crops have a slow growth period. Farmers need to strengthen the construction of farmland drainage facilities to reduce the impact of disasters. At the same time, prevent geological disasters such as mudslides and landslides caused by heavy rainfall.
From the perspective of benefiting and avoiding harm, autumn rain in western China is beneficial to ponds and paddy fields in arid areas.
(Responsible editor: Luan Fei)