What are the characteristics of the 6.22 super-historical rainstorm and flood in Hunan?

Recently, Hunan Provincial Defense Office organized provincial meteorological and hydrological departments to comprehensively analyze the heavy rainfall process from late June to early July. Due to the frequent confluence of cold and warm air, continuous heavy rainfall occurred in most areas of Hunan from June 22 to July 2 (hereinafter referred to as "June 22"), which eventually led to catastrophic floods in Xiangjiang River Basin, Zishui and Shui Yuan and Dongting Lake areas, causing huge disaster losses to Hunan.

Since the beginning of this year (65438+1 October1July 12), the cumulative average precipitation in the whole province has been 105 1.5 mm, which is a little more than the average of 9 15.9 mm/kloc in the same period over the years. Since the flood season (April 1 to July 12), the cumulative average precipitation in the whole province is 743.2 mm, which is more than the average of the same period in previous years 16. 1%. Since June 1 entered the main flood season, there have been many days of heavy rains in the province, especially from June 22 to July 2, when unprecedented heavy rains and floods occurred.

The weather cause of this rainstorm and flood is mainly caused by the interaction between the northern cold vortex and the subtropical high. The position of the western Pacific subtropical high is relatively stable. The rain belt of Meiyu front formed in Hunan on the 22nd swings, and the water vapor channel is relatively stable. Hunan is located on the edge of subtropical high, on the strong water vapor conveyor belt, and has a continuous water vapor supply. At the same time, the cold vortex system in the north maintained for a long time, and the cold air continued to spread southward at the back of the cold vortex, and the cold and warm air frequently met over the south, leading to continuous heavy rain in Hunan.

The rainstorm belt swings back and forth in Hunan in three stages. It was located in north-central Hunan on June 22-24, moved to south-central Hunan on June 25-28, and moved to north-central Hunan on July 29-2.

This rainstorm and flood has six basic characteristics:

1, cumulative rainfall. In June, the total rainfall in the whole province reached 407. 1mm, which was 1.7 times of the average rainfall in the same period of many years, 23mm more than the maximum rainfall of 65438+June 0954 and 70mm more than 65438+June 0998. On June 22nd, the average rainfall in the whole province was 270mm, of which the rainfall from June 29th to July 2nd reached117mm. From the distribution of river basins, Xiangjiang River was 326.3mm, Zishui River was 345.8mm, Yuanjiang River was 248.6mm, Lishui River134.3mm, and Lishui River was 248.6mm.. In terms of city and state distribution, the largest is 452.0mm in Changsha, followed by 387.0mm in Yueyang and 375.7mm in Loudi. Yiyang, Xiangtan and Shaoyang also reached 363.9 mm, 322.3 mm and 365,438+02.8 mm respectively. 83 counties, 59 counties and 23 counties have rainfall exceeding 300 mm. The maximum rainfall at the cumulative point is 824.0mm at Yuquan Station in daweishan town, Liuyang City, followed by Hanpo Station in Gugang Town, Liuyang City, 7 19.0mm, and Sandu Water Station in Guanzhuang Town, Yuanling County, 690.0mm.

2, the duration is long. It rained for 20.5 days on June 30th, and the "June 22nd" process lasted until July 5th, and it rained for 25 days. Among them, the concentrated rainfall duration on "June 22nd" was 1 1 day, which was 195 1 year (1day, July17-26th, 2002), and the regional rainstorm (≥

There is a lot of rainfall during this period. The rainfall intensity in many places is particularly high, and the maximum rainfall 1 hour, 3 hours and 6 hours are 1 57mm respectively (July 1 day in Longhui county 1-2 hours, and July1day in Ningxiang county189mm).

4. The scope of influence is wide. The heavy rainfall on June 22nd covered most of the province, including 88,000 square kilometers with rainfall exceeding 300mm, mainly including the lower reaches of Xiangshui River, Zishui River Basin, Yuanshui River Basin and East Dongting Lake area. The rainfall area of over 500mm is 8,000 square kilometers, mainly including the lower reaches of Xiangshui River, Zhexi Reservoir in Zishui Basin, Wuqiangxi Reservoir in Shui Yuan Basin and Miluo River Basin in Lake Area. The water levels in Xiangshui, Shui Yuan, Zishui and Dongting Lake areas have risen in an all-round way, and there has been a rare "three parallel rivers" flood.

The water level of the river is very high. Affected by heavy rainfall, there were basin floods in Xiangjiang River and floods in Zishui and Yuanjiang River. Xiangjiang River, Zishui River and Yuanjiang River meet in Dongting Lake at the same time, forming a flood in Dongting Lake, which is rare for many years. Among them, the entire Xiangjiang River, Yuanjiang River and Zishui River, except Lengshuijiang to Xinhua River, all half of the dikes in Dongting Lake area exceeded the guaranteed water level. The province exceeded the police 104 stations, of which 29 stations exceeded the insurance, and 13 stations exceeded the history.

At 0: 12 on July 3rd, Xiangshui Changsha Station reached the peak water level of 39.5 1m, exceeding the warning water level of 3.5 1m, which was 0.33m higher than the measured historical highest water level of 1998, and the flood return period was once in 50 years. Floods exceeding the measured historical highest water levels of 0. 14m, 0.59m, 0.7 1m occurred in Laobutou Station in Lingling District, Qiyang Station in Qiyang County and Guiyang Station in Qidong County, respectively, and the flood return period reached once every 30 years, 50 years and 50 years. The flood peak water level of Xiangtan Station of Xiangjiang Control Station is 41.23m, which is the third in the history and the highest since 1.995. The flood peak water level of Zishui Taojiang Station is 44. 13m, which is only 0.02m away from the highest water level in history. The return period of flood is about once every 30 years. The peak water level of Taoyuan Station in Shui Yuan is 45.43 meters, and the flood return period is about once every 30 years.

There are many tributaries such as Lianshui, Liuyang River, Laodao River and Weishui River in the lower reaches of Xiangjiang River, Fuyi Water, a tributary of Zishui, and Zhushui, a tributary of Shui Yuan, which have been flooded. Among them, the floods in Loudi Station of Lianshui, Xiangxiang Station, Langli Station of Liuyang River, Luohanzhuang Station of Laodao River and Ningxiang Station of Weishui exceeded the measured history by 2.6 1 m, 0.0 1 m, 0.75 m, 1.63 m and 0.23 m respectively, and the flood return period reached 65,438 respectively. A flood of 1.36 m exceeding the measured history occurred at Xinning Station of Fuyishui, with a recurrence period of 50 years. A flood exceeding the measured history of1.54m occurred at Dangping Station of Yanzhu Bamboo Water.

6. The flow into the lake is very large. In the "Four Rivers" of Xiangzi Ethan, Xiangshui, Zishui and Shui Yuan were almost flooded at the same time, and the flood peak encountered a bad combination in Dongting Lake. The total flow into the lake reaches 865,438+0,500 second cubic meters, which is the maximum flow into the lake since the data are available. In contrast, the maximum flow into the lake is 65,438+0,954 and 65,438+0,998. As a result, the water level in Dongting Lake area rose rapidly, and the flood control levees in line 347 1 km in Dongting Lake area exceeded the warning water level, and the levees in line 1/2 exceeded the guaranteed water level. Because the discharge of the Three Gorges Reservoir has been reduced many times, it is beneficial for Dongting Lake to leave the library, reaching a maximum of 49,400 cubic meters. The flood peak water level of Chenglingji Station still reaches 34.63m, exceeding the warning water level by 2.13m, exceeding the guarantee by 0.08m, ranking the fifth in historical measurement.

Doing a good job in flood control and fighting is a prepared battle, and it is necessary to have foresight and nip in the bud.