Storm flood is the main source of flood disaster in China. Under the influence of continental monsoon climate, rainfall is concentrated and intense in most parts of China. Except for northern Xinjiang and southern Hunan, more than 50% of the annual rainfall in most areas is concentrated in May-September. Among them, 70-90% of the areas north of Huaihe River, northwest, southwest, south of South China and most of Taiwan Province Province, and 50-70% of the areas north of Huaihe River to north of South China are concentrated in May-September. There are four rainstorm-prone areas in eastern China: (1) from the southeast coast to the south of Guangxi, including Taiwan Province Province and Hainan Island, the hourly rainfall can reach more than 500 mm; (2) From Liaodong Peninsula, along the Haihe River, Yellow River and Huaihe River basins east of Yanshan Mountain, Taihang Mountain, Funiu Mountain, Wushan Mountain and the middle and lower reaches of the Yangtze River, the 24-hour rainstorm can reach more than 400 mm; There have been records of rainstorms over 600- 1000 mm at the southern foot of Taihang Mountain and the southeast slope of Funiu Mountain. (3) In Sichuan Basin, especially in northwest Sichuan, the 24-hour rainstorm often reaches more than 300 mm; (4) There is heavy rain at the junction of Inner Mongolia and Shaanxi. High-intensity, large-scale and long-term rainstorms often form floods with high peaks and large flows. There are 738,000 square kilometers of land in the eastern region below the river flood level, and 40% of the population, 35% of the cultivated land and 60% of the total industrial and agricultural output value are seriously threatened by floods. However, these areas develop agriculture for one factory and one industry, expand cultivated land, build dikes, reclaim land around lakes and compete for land with water. As a result, flood discharge outlets and flood storage and detention areas are constantly restricted, and natural flood storage capacity is constantly decreasing and shrinking; Coupled with the extensive reclamation and utilization of land in hilly areas, the destruction of forest vegetation, the formation of residential areas, cities and traffic roads, and the changing state of the surface, the conditions of flood generation and confluence are constantly changing, thus increasing the harm of floods.
Affected by climatic and geographical conditions and socio-economic factors, floods in China have the characteristics of wide range, frequent occurrence, strong suddenness and great losses.
1. Wide range. Except for desert, extremely dry area and extremely cold area, about 2/3 of China's land area has different degrees and types of floods. There is a lot of precipitation in the whole year, 60-80% of which is concentrated in the eastern region. The flood season is from June to September, and heavy rains and floods often occur. Mountain torrents and mudslides often occur in mountainous, hilly and plateau areas, which account for 70% of the national territory. Some coastal provinces, autonomous regions and municipalities directly under the central government are hit by floods caused by storm surges every year. The Yellow River, Songhua River and other rivers in northern China sometimes cause floods due to freezing; Snowmelt floods occur every day in Xinjiang, Qinghai, Tibet and other places; Floods caused by reservoir dam break and man-made dam break also occur from time to time.
2. It happens frequently. According to the statistics of Ming History and Qing History Draft, there were 424 floods in the Ming and Qing Dynasties in 543 (1368-1911), involving several counties to 30 counties, with an average of three floods every four years, including more than 30 floods. Since the founding of New China, floods have occurred every year, but the scale is different. Especially in 1950s, there were 1 1 floods every year.
3. Suddenly. Heavy rains with large intensity and wide range often occur in the eastern part of China, and the flood control ability of rivers is low, and the flood disaster is sudden. During the period of 1963, there was still a large area of drought in the south of Haihe river basin at the end of July, and heavy rain suddenly fell from August 2 to 8, causing a rare flood disaster in this area. Debris flow in mountainous areas is more sudden. Once it happens, people often have no time to retreat, causing heavy casualties and economic losses. For example, 199 1, more than 200 people died in the Huaying Mountain mudslide in Sichuan, 199 1, and more than 200 people died in Zhaotong, Yunnan. The same is true of storm surges. For example, from August 3 1 day to September 2 1992, influenced by astronomical climax and typhoon 16, the tidal level in the coastal areas from Shacheng, Fujian to Ruian and Aojiang, Zhejiang Province exceeded the highest level since liberation. The tidal level in Shanghai is 5.04m, and that in Tianjin is 6.14m. Many seawalls were flooded and destroyed.
4. Great loss. For example, in 193 1 year, the Jianghuai flood involved eight provinces of Henan, Shandong, Jiangsu, Hubei, Hunan, Jiangxi, Anhui and Zhejiang, flooded farmland/kloc-0.46 million mu, and the affected population was 5 127 million, accounting for 25% of the total population of the eight provinces at that time, and died. 199 1 year, floods occurred in some rivers such as Huaihe River, Taihu Lake and Songhua River in China. Although under the leadership of the CPC Central Committee and the State Council, the people of all ethnic groups throughout the country have carried out fruitful fighting against floods and minimized disaster losses, the affected area in the country still reached 368 million mu, with direct economic losses as high as 77.9 billion yuan. Among them, the direct economic loss of Anhui Province reached 24.9 billion yuan, accounting for 23% of the total industrial and agricultural output value of the year, and the affected population was 44 million, accounting for 76% of the total population of the province.
Second, the flood disaster losses since the founding of the People's Republic of China
Since the founding of New China, the flood-affected area has averaged 65.438+0.34 billion mu per year, and the affected area is 76 million mu, resulting in tens of billions of direct economic losses.
In the 45 years from 1950 to 1994, the affected area exceeded 1953, 1954, 1956, 1957, 1958. The years when the affected area exceeds 1 100 million mu are 1.954, 1.956, 1.963, 1.964, 1.985 and/kloc respectively.
The losses caused by floods in China since the founding of the People's Republic of China have the following characteristics:
1. Major floods (including major floods and catastrophic floods) occurred in large rivers, and the losses caused by floods were the greatest.
Since the founding of the People's Republic of China, the years of major floods have been: 1954 (Yangtze River and Huaihe River), 1956 (Haihe River and Huaihe River), 1963 (Haihe River and Huaihe River), 1985 (Ile River) and 65438+. In recent years, the flood-affected area in China has exceeded 200 million mu, and the flood-affected area has exceeded 65.438+0 billion mu respectively, which is 654.38+0.5-2.8 times of the multi-year average (see Table 2-654.38+0).
In recent years, the flood-affected area and the disaster-affected area of the catastrophic flood basin accounted for 47-90% of the national disaster-affected area and disaster-affected area respectively. For example, in 1963, the Haihe River and Huaihe River basins were flooded, and the affected areas of Hebei, Beijing, Shandong, Jiangsu, Henan, Anhui and other provinces and cities in the two river basins were168.98 million mu, accounting for 80% and 90% of the national affected areas respectively. During the period of 1985, a serious flood disaster occurred in Northeast China, and the affected areas in Liaoning, Jilin and Heilongjiang provinces accounted for 47% and 53% of the country respectively. This fully shows that the major disaster losses in these years are mainly caused by the major floods in major rivers.
Table 2- 1 Flood-affected area and affected area unit: 10,000 mu.
Affected area
diaster area
Reserve bill
1950 ——1994 average
1954
1956
1963
1985
199 1 year
1994
13 754
24 197( 1.8)
2 1 566( 1.6)
2 1 107( 1.5)
2l 296( 1.5)
36 894(2.7)
28 288(2. 1)
7 8 1 1
16 958(2.2)
16 358(2. 1)
15 7 19(2.0)
13 424( 1.7)
2 1 92 1(2.8)
l7 234(2.2)
Missing data for 1967- 1969.
The Yangtze River and Huaihe River are flooded.
The Haihe River and Huaihe River are flooded.
The Haihe River and Huaihe River are flooded.
Liaohe flood
The Huaihe River and Taihu Lake basins are flooded.
The Pearl River overflows.
Attention; The figures in brackets indicate that the affected area and the affected area in that year are multiples of the average value of 1950 ~ 1994.
2. The flood disaster losses of seven major river basins and coastal rivers in provinces, autonomous regions and municipalities directly under the Central Government account for a large proportion of the total flood disaster losses in China.
According to 1950 to 1 994 (missing 1967- 1969), the total area affected by floods in China is 5,635.54 million mu, and the total area affected by floods is 3,202.37 million mu. Hubei, Hunan, Jiangxi, Anhui, Jiangsu, Zhejiang, Shanghai, Shaanxi, Shanxi, Henan, Shandong, Liaoning, Jilin, Heilongjiang, Inner Mongolia, Fujian, Guangdong, Guangxi, Beijing, Tianjin, Hebei, Hainan, Sichuan and Guizhou in the upper reaches of the Yangtze River. The flood-affected area is 55,535110,000 mu, and the flood-affected area is 3,080.84 million mu, accounting for 99% and 96% of the total flood-affected area in China respectively. Among them, Hebei, Liaoning, Jilin, Heilongjiang, Jiangsu, Zhejiang, Anhui, Jiangxi, Shandong, Henan, Hubei, Hunan, Guangdong, Guangxi, Sichuan, Shaanxi and other 16 provinces (referred to as 16 provinces, the same below) accounted for 86% of the total area affected by floods and the total area affected by floods respectively.
Table 2-2 Flood Statistics Unit and Affected Area Stage: 10,000 mu
project
Entire country
25 provinces, autonomous regions and municipalities directly under the Central Government
16 province
Surface product
It accounts for% of the country.
Surface product
It accounts for% of the country.
1950 to
Affected area
563 554
555 35 1
99
498 880
Eighty-nine
1994
diaster area
320 237
308 084
96
289 030
94
1955 to
Affected area
299 307
296 572
99
265 203
Eighty-nine
1980
diaster area
177 698
168 323
95
162 964
92
198 1 year to
Affected area
264 247
258 779
98
229 448
Eighty-nine
1994
diaster area
142 539
139 76 1
98
124 896
Eighty-nine
Note: ① The 25 provinces, autonomous regions and municipalities directly under the Central Government refer to Hubei, Hunan, Jiangxi, Anhui, Jiangsu, Zhejiang, Shanghai, Shaanxi, Shanxi, Henan, Shandong, Liaoning, Jilin, Heilongjiang, Inner Mongolia, Fujian, Guangdong, Guangxi, Beijing, Tianjin, Hainan, Sichuan, Guizhou, Yunnan and Hebei.
② 16 provinces refer to Hebei, Liaoning, Jilin, Heilongjiang, Jiangsu, Zhejiang, Anhui, Jiangxi, Shandong, Henan, Hubei, Hunan, Guangdong, Guangxi, Sichuan and Shaanxi.
The reasons for this situation are as follows: firstly, the annual rainfall in these areas is large, more than half of which is concentrated in May-September, so floods often occur; Second, these areas account for 35% of the country's cultivated land, 40% of the population and 60% of the total industrial and agricultural output value. In the event of a flood, the loss will be even greater.
3. 198 1 to 1994, among the 5654 1 people who died due to floods, there are 20045 people in Sichuan, Shaanxi, Yunnan, Guizhou and other provinces prone to mountain torrents and mudslides, accounting for about 35%; In Zhejiang, Fujian, Guangdong, Hainan and other provinces, 9999 people were frequently hit by typhoons, accounting for about18%; There are 13500 people in Hubei, Hunan, Henan and Jiangxi provinces with frequent disasters, accounting for about 24%. There were 43,544 deaths in the above-mentioned 13 provinces, accounting for 77% of the national death toll (see table 2-3).
Table 2-3 198 1 to 1994 flood deaths: number of people.
Death toll
Accounted for% of the national death toll
National total
Sichuan Province
Shanxi province
Yunnan Province
Guizhou (province)
Subtotal of four provinces
Guangdong (Hainan)
Zhejiang Province
Fujian Province
San Xiao sheng zhi
Anhui province
Hunan
Hubei province
Henan Province
Jiangxi
Subtotal of five provinces
56 54 1
8 668
4 839
3 669
2 869
20 045
3 406
3 880
2 7 13
9 999
2 596
3 682
2 488
2 286
2 448
13 500
100
15
nine
six
five
35
six
seven
five
18
five
seven
four
four
four
24
This shows that, on the whole, mountain disasters such as mountain torrents, mudslides, landslides, falling rocks and typhoons pose a great threat to people's lives, except for super-standard floods in large rivers, which lead to dam failures of rivers and reservoirs and cause a large number of casualties.
4. Except for Beijing, Tianjin, Hebei, Shanghai, Shandong and Henan, the flood-affected areas and the annual average of the flood-affected areas in other provinces 198 1 994 are greater than 1950/980. From 198 1 to 1994, the national average annual affected area is 18875 mu, and the affected area is10/0/810000 mu, respectively, while the annual average. Among them, 25 provinces, autonomous regions and municipalities directly under the central government increased by 75% and 66% respectively; 16 provinces increased by 73% and 53% respectively (see table 2-4). This shows that since 1980s, floods have done more harm to most areas of China. The main reasons are as follows: First, since 1980s, China's population has increased and its economy has developed rapidly, and flood control construction has lagged behind the speed of population growth and economic development. What's more, the blind development and occupation of the river beach reduces the flood discharge capacity of the river; Second, most of the existing flood control projects were built in the 1950s and 1960s. Many of them have been in disrepair for a long time, operated with diseases, and served for an extended period, and their flood control capacity has been reduced.
Table 2-4 Average Disaster Situation and Affected Area Stage Comparison Unit: ten thousand mu
1950— 1980
198 1- 1994
Percentage after 198 1 year
Average annual disaster
zone
Annual disaster
zone
Average annual disaster
zone
Annual disaster
zone
Average annual disaster
zone
Annual disaster
zone
Entire country
25 provinces, autonomous regions and municipalities directly under the Central Government
16 province
10 690
10 592
9 472
6 346
6 0 1 1
5 820
18 875
18 484
16 389
10 18 1
9 983
8 92 1
77
75
73
60
66
53
Third, the flood disaster prevention system in China
The flood control system of major rivers in China consists of engineering measures and non-engineering measures. About 245,000 kilometers of reinforced dikes and 2,900 kilometers of dampproof dikes have been built nationwide. Focus on dredging rivers, expanding and opening channels for Huaihe River and Haihe River floods to enter the sea, and later regulating Liaohe River, Songhua River and Taihu Lake; 82,848 reservoirs were built with a total storage capacity of 4610.70 billion cubic meters, including 358 large reservoirs with a total storage capacity of 335.7 billion cubic meters; More than 100 flood storage areas have been opened in major rivers, with a flood storage capacity of about12 billion cubic meters; Vigorously promote soil and water conservation, and initially control soil erosion with an area of about 500,000 square kilometers. Digital microwave communication trunk lines from Zhengzhou to Sanmenxia in the Yellow River Basin, Xinyang to Bengbu and Xuzhou in the Huaihe River Basin and newly-built 800-megabit communication systems from Tianjin to Langfang, Beijing and Zhuoxian in the Haihe River Basin have been built. Construction of more than 8,500 hydrological flood stations and 1 1,000 hydrological forecasting stations; A set of flood forecasting system suitable for VAX- 1 1 series computers has been preliminarily established and applied to flood forecasting of large rivers. More than 20 automatic hydrological forecasting systems and about 500 telemetering stations have been built in Sanhua reach of the Yellow River, Jingjiang reach of the Yangtze River, the basin above Zhengyangguan of the Huaihe River, Guanting Gorge of Yongding River, Sanjiangkou area of Liaohe River and Taihu Lake area. There are 299 large reservoirs and 43 key dangerous reservoirs in China, and 150 reservoirs have built automatic hydrological forecasting systems, and there are about 1200 telemetry stations. Eighty-five alarm center transmitting stations and 10428 alarm receiving points have been established in 25 key flood storage and detention areas in the Yangtze River, Yellow River, Huaihe River and Haihe River basins. More than 30 flood control departments have installed equipment to receive Japanese GMS satellite cloud images; Modern means, such as remote sensing, have been used to transmit images about flood control. Flood control headquarters have been established at the central, provincial, prefecture, city and county levels, and the flood control responsibility system with the chief executive responsibility system as the core has been implemented; Mobile flood control teams have been established in key areas; The state has formulated laws and regulations such as the Water Law, the Regulations on Flood Control and the Regulations on River Management, and formulated flood control plans for major rivers. Pilot flood control insurance, and so on.
The flood control system formed by major rivers can make the Huayuankou in the lower reaches of the Yellow River pass the flood flow of 22,000 cubic meters per second, and with the cooperation of Beijindi and Dongping Lake flood storage and detention area, the two major floods in this century, namely ]933 and 1958, can be safely discharged, and the flood control standard is about once every 60 years; The flood control standards of Lanzhou and Ningmeng reach in the upper reaches can reach 1, once every 0,000 years and once every 50 years respectively. The standard of dikes in the main stream of the middle and lower reaches of the Yangtze River, the lower reaches of Hankang and the lake area can reach 10-20 years, with the cooperation of flood diversion and storage areas. It can defend against 1954 flood. With the cooperation of various flood control measures in Haihe River system, rivers in the northern river system can defend against 1939 flood, and rivers in the southern river system can defend against 1963 flood. The flood control standard for each river is once every 50 years. Middle and lower reaches of Huaihe River. It can prevent 55 floods in 1954, which is equivalent to once in 40 years; The lower reaches of Yishu Sihe River can defend against the flood with a return period of 10-20 years. Xijiang River and Dongjiang River in the Pearl River Basin can defend against floods that occur once in 20-50 years. Beijiang levee can defend against the flood of 100 years; The five purse seines in the Pearl River Delta region can defend against the once-in-50-year flood. The main stream of Songhuajiang River can defend against 10-20 year flood; The main stream of Liaohe River can defend against the once-in-20-year flood.