Characteristics of Rainstorm and Flood Disaster in

Meteorological and Environmental Research 2018, 9(3) ：75 -78 , 82Characteristics of Rainstorm and Flood Disaster in Shaoyang City and Flood Protection CountermeasuresTang Zuoyang1, Lv Weiwei2, Lv Xiaohua1", Tang Yaqiong1, Tan Dequan11. Shaoyang Meteorological Office, Shaoyang 422000, China；2. Xinshao Meteorological Office, Xinshao 4229CX), ChinaAbstract Based on ground meteorological observation data at 10 representative stations of Shaoyang City during 1951 -2017 and rainfall data at over 220 automatic weather stations during 2005 -2017, statistical analysis on rainstorm and flood disaster in Shaoyang was conducted. Occurrence characteristics and rule of rainstorm and flood disaster were found, and disaster situation was evaluated and analyzed. The results showed that (1) there was almost local rainstorm and flood in Shaoyang City every year, with strong seasonal characteristic. (2)The loss caused by rainstorm and flood disaster was the most serious in various meteorological disasters. (3) Rainstorm and flood disaster generally had the sudden and devastating characteristics. Via the analysis and research on rainstorm and flood disaster, defense measure and countermeasure of rainstorm and flood were proposed, which could provide scientific decision basis for party and government leading flood relief, and had important guidance significance for preventing and mitigating disasters by government agencies.Key words Rainstorm；Flood disaster；Urban flood control；Flood control measures and countermeasuresDOI 10.19547/j. issn2152 -3940.2018.03.017Flood is one of main disasters in China's cities. In China, most cities are built in the waterfront, and they all have the problems of flooding and waterlogging after the rainfall. Ac­cording to incomplete statistics, the flood incident with more than 0.1 million deaths could occur per 15 years, while the flood incident with more than 1million deaths could occur per 60 -70y e a rs11. In the past 60 years, due to uneven tempo­ral-spatial distribution of rainfall, rainstorm and flood disaster occurred frequently in Shaoyang City, which brought extreme­ly serious impact on economy in Shaoyang City especially ag­ricultural production and eco-environment. Therefore, it is very important to study the characteristics and countermeas­ures of rainstorm and flood disaster in current domestic disas­ter research[2_5], and it is also important topic of disaster pre- vention and decision services by meteorological departments at all levels. In recent 20 years, a lot of analysis and research on rainstorm and flood disaster were conducted by domestic scholars or professionals, and fruitful results were achieved. But the research was not deep enough on the whole, with cer­tain limitation. Huang Zhaoying et al.[6] comprehensively and objectively analyzed the impact characteristics and type of rainstorm and flood on road traffic, and constructed mathe­matical models of objective statistics on destructed length of road base and the affected rural paddy area by the flood. Based on rainstorm and flood data in Ningxia over50 years, Li FengqinC7]summarized occurrence rule and characteristics of rainstorm and flood disaster and its influence on industrial and agricultural production from the aspects of total rainfall occur­rence times and occurrence period of heavy rainfall. Based on Meiyu data of Jiangsu Province over 50 years, Tian Xinru *Received：March 15, 2018 Accepted：May 7, 2018* Corresponding author. E-mail：syqxtlxh@ et al.[8] carried out disaster risk analysis and post evaluation on Meiyu and flood disaster by mathematical statistics. Started from actual demand of flood and drought prevention and con­trol ,Xu Xiangyang et al.[9] proposed the necessity of con­structing assessment system of flood and drought disaster loss, and analyzed and described the structure, function and effect of the system in detail. According to rainstorm charac­teristics and rule in Tianjin City and urban drainage operation rules of water conservancy department in flood season, Xie Yiyang et al.[10] used mathematical model of urban ponding and waterlogging disaster in Tianjin to simulate various types of rainfall processes. Meanwhile, shallow quantitative assess­ment on rainstorm inducing urban waterlogging disaster was conducted. But there was less research on zoning and de­fense countermeasures of rainstorm and flood disaster. There­fore, there are a lot of new problems that deserve our discus- sion on prevention and control measures of urban rainstorm and flood disaster. For example, one short-term or continuous strong rainfall weather occurred in the low-lying region of urban and rural areas and the place where the terrain was obliterate. Because that strong rainfall could not be quickly discharged, it caused urban street ponding, excessive farmland ponding, and oversaturation of soil moisture, thereby bringing serious disaster for agricultural production, even inducing local land­slides, flash floods, river flooding, and reservoir dikes dam­age, and causing large loss on the people's life and property and the national economy. The rainstorm of Shaoyang in 1996 caused serious waterlogging in whole urban district of Shaoy­ang. Due to mountain torrents by rainstorm on June 19, 2001, heavy casualties in Suining were caused. Therefore, it is urgent to study the rule and characteristics of rainstorm and flood disaster, and find the most economic and effective pre­vention and control countermeasures, which is also urgent76Meteorological and Environmental Research 20182.2 Temporal-spatial distribution characteristics of rainstorm (1) There were 1 625 times of single-station rainstorm and 132 heavy rainstorm in Shaoyang City in 67 years, in which there were 107 times of regional rainstorm (m ore than 5 sta­tions) from 1960 to 2017. There were 58 times of rainstorm in whole city every year, and the earliest rainstorm occurred on February 1, 1983, while the latest rainstorm occurred on De­cember 18, 2002.(2) Temporal distribution of rainstorm and heavy rainstorm in Shaoyang City was very uneven. The most rainstorm or heavy rainstorm occurred in 1994, and there were 67 rainstorm stations (daily rainfall of 50.0 -99.9 m m ), while there were 11 stations of heavy rainstorm. The least rainstorm or heavy rain­storm occurred in 1963, and there were only 10 times of rain­storm, without heavy rainstorm. Rainstorm and heavy rain- storm in Shaoyang concentrated in June, which accounted for 27.1% and 38.3% in whole year. By analyzing daily changes of heavy rainstorm and rainstorm, it was found that heavy rain­storm and rainstorm in Shaoyang mainly concentrated in night, namely 20 ：00 -08 ：00.(3) Heavy rainstorm or rainstorm times in Shaoyang City was positively proportional to annual rainfall at representative station. Dongkou where annual average rainfall was the most had the most heavy rainstorm or rainstorm days in Shaoyang City, and there were 75 d of heavy rainstorm days and more than 206 d of rainstorm days. Annual average rainfall in Cheng- bu was the least，its corresponding rainstorm or heavy rain­storm days was the least ， and they were respectively 120 and 5 d (Fig. 1). For whole city, rainstorm was more in the south­west and less in the northeast both in frequency and intensity.(4) Rainstorm was the most in June, followed by May, and there was no rainstorm in January (F ig.2).Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sept. Oct. Nov. Dec.MonthFig. 2 Total rainstorm days in each month of 1951 -2017need of disaster prevention and reduction by meteorological departments and local governments at all levels, and has very important economic and social significance for social and eco­nomic development, constructing social harmony, protecting peopled life and property safety, eco-environment construc­tion ,the construction of intelligent city.1Data source and methods1.1Data source Rainstorm and flood data at 10 nationalbasic stations and reference stations of Shaoyang City during 1951 -2017 and 24 h of rainstorm data at 228 automatic weather stations of Shaoyang City during 2005 -2017 were used.1.2 Standard and methods The rainstorm in this paper in­dicates heavy rainfall occurred in short time. According to the stipulation by Central Meteorological Observatory, taking 20：00 as the boundary of a day(20 ：00 - next 20 ：00), it is called rain­storm when 24 h of total rainfall is 50-100 mm (not containing 100 m m )，heavy rainstorm when 24 h of total rainfall is 100 -250 mm (not containing 250 m m ), and extremely heavy rainstorm when 24 h of total rainfall is ^250 mm. Flood refers to local standard of Hunan. Slight flood, the following two items, reaching any one of them. (1) Total rainfall in any 10 days of April - September is 200 -250 m m ； (2) total rainfall during April - September is 20% - 30% more than that in the same period of the past years. Moderate flood, the following two, reaching any one of them. (1) Total rainfall in any 10 days of April - September is 251 -300 m m ； (2) total rainfall during April - September is 30% - 40% more than that in the same period of the past years. Severe flood, the following two, reaching any one of them. (1) Total rainfall in any 10 days of April - September is more than 301 m m ； (2) total rainfall dur­ing April - September is 40% more than that in the same period of the past years. Using mathematical statistics and normaliza­tion ,the related disaster risk index and disaster risk rating were calculated.2 Rainstorm and flood characteristics in Shaoyang City2.1 General situation of rainstorm and floodShaoyangCity belongs to typical middle subtropical monsoon humid cli­mate zone. Average rainfall in whole city is between 1 204 (Chengbu) mm and 1 506 (Dongkou) mm, and temporal-spa­tial distribution of rainfall is extremely uneven. The most annual rainfall was 2 130.8 mm in Xinshao in 1991, while the least an­nual rainfall was 859.4 mm in Shaodong in 1994. The rainfall mostly concentrated during March - August, occupying 70% of annual rainfall, and rainfall during April - June was especially concentrated, accounting for 42% of annual rainfall. Rainstorm mainly concentrated during April - August, while heavy rain­storm more than 100 mm mainly concentrated during June - August. Due to the influence of geographical terrain, Dongkou County is one of centers with abundant annual rainfall in whole province. Rainstorm is easy to cause flood disaster, and flood is accompanied with rainstorm.nq 3§63.S U U 一 xS U -S -300§u a %c x o uopomls^*_3S篆 o m l GOno)3UOQ一nqsuoTo m l s.2xs5191n gU rdn o a t i S tc hea of d a y s r mo r S t p f | S >.a 3pm j c n s u l ^0'0'<±>0'沙 a n l 7 6 5 4 3 21p//s ^p s J c n s u l^Tang Zuoyang et al.Characteristics of Rainstorm and Flood Disaster in Shaoyang City and Flood Protection Countermeasures773 Historical disaster situation and charac­teristics of rainstorm and flood in Shaoyang City3.1 H istorical disaster situation o f rainstorm and flo o d Rainstorm and flood disaster frequently occurred in Shaoyang City. According to yearbook data of Shaoyang, 74 times of flood occurred in recent 300 years, once every 4 years. And there was flood disaster in 24 years of 1950 -2016, about once every 3 years. Due to abrupt occurrence of flood in mountain area, although duration was short, it brought serious loss for people's life and property and national economy. A total of 41 people died in the flood of the city in 1988, hurting 125 people. The largest flood disaster occurred in Shaoyang in middle dek- ad of July, 1996, and the flood disaster had regional and dev­astating features. At 02：00 on July 18, the highest water level of flood peak at Linjinmen Hydrological Station of Zijiang River stream was 222.21 m, which exceeded alert level by 8.21 m and created the highest water level in Shaoyang. 196 towns in 3 districts, 1city and 8 counties suffered from different degrees of disaster, and farmland and some houses in urban district were submerged, in which 71 towns suffered serious disaster, accounting for 36.2%. In 7.04 million people, 5.160 5 million people were affected, accounting for 73.3%, 0.688 3 million people were surrounded by flood, 0.422 3 million people were urgently transferred, and 82 people died in the flood. 0.137 7 million houses were collapsed, 1524. 73 km2of agricultural crops were affected, and direct economic loss was 7.5billion yuan, in which direct economic loss of water facilities was 0.087 3 billion yuan. The flood in Shaoyang was caused by long-time rainstorm, inducing that agricultural crops in riverside and low-lying areas were submerged. Serious flood disaster in the history was caused by rainstorm with large intensity and long duration, as well as bad flood control measures. Rain­storm and flood often destroyed dike, house, road, bridge, submerged agricultural crops, erodes soil, and induced debris flow and landslides due to large intensity. It not only caused se­rious loss of agricultural production but also harmed life safety of human and animal, and was a kind of especially serious nat­ural disaster.3.2 Characteristics of rainstorm and flood disaster Rain­storm and flood always occurred in Shaoyang City year after year, and typical cases included regional flood in whole city during July 12 -18, 1996, extraordinary flash flood in Suining on June 19, 2001, extraordinary flash flood in Xinshao on May 31,2005, debris flow disaster induced by 6. 25 rainstorm of Longhui in 2006, rainstorm and flood disaster on May 25, 2014, regional flood and disaster in last dekad of June, 2017.Via the analysis on above 6 cases, rainstorm and flood disaster in Shaoyang City had below characteristics and rules.(1) High occurrence frequency and strong seasonal char­acteristic. Rainstorm and flood disaster almost occurred every year, and generally appeared from late spring to summer (M a y-J u ly).(2) Short time and strong abrupt occurrence. Local rain­storm and flood often caused the disaster in short time, only needing several hours and even 1hour. The flood flowed into the river, causing that water level of urban river quickly rose.(3)Ferocious intensity, large truculency, and serious casualties. The heavy rainfall forming flood mostly had fero­cious intensity, and any thing was destroyed where the flood came, which destroyed large-range farmland and house, with very serious casualties.(4) Large local rainstorm intensity and regional unfixity. Seen from rainstorm and flood disaster in the past years, high- intensity rainfall was direct cause for the disaster. But local in­tensity of rainfall was large, with regional unfixity. Especially in mountain area, rainfall with high intensity could occur in every area, and its accurate forecast was difficult.(5) Urban rainstorm flood was often formed by heavy rain­fall in mountainous area. After rainstorm flood appeared, the flood flowed from creek to river and tributary to stream, which was pretty fast. It made urban river water quickly rise and caused urban flood disaster.4 Countermeasures of urban flood preven­tion and drainageFlood disaster is one of main natural disasters in China’s cities. Most cities in China are built in waterfront, with relatively low terrain, and they face flood and waterlogging problem after the rainfall. According to related data, more than 500 cities need flood control in China, and many cities suffer serious threatening from river flood to different degrees. Therefore, ur­ban flood control and drainage situation is severe, and it should fully respond to the flood and make countermeasures, to ear­nestly and effectively solve problem. So, each city need estab­lishing effective flood prevention measures and making flood control countermeasures to promote urban flood control and drainage ability.4.1 Control heat island effect and protect clim ate envi­ronment It should strictly control urban large-scale energy consumption and heat discharge, advocate energy saving and emission reduction, and protect atmospheric environment, thereby avoiding climatic and environmental change induced by a slice of urban heat island effect, and reducing frequent occur­rence of rainstorm flood.4.2 Perfect the plan and supervise it in place The gov­ernment department should perfect emergency plan of urban flood control and drainage. According to the plan, it should check and dredge all drainage pipe network in urban district be­fore flood period, and maintain the facilities, to ensure perfect drainage system, normal device operation and unobstructed drainage. The cities at all levels should strictly do a good job of rescue and emergency preparation. In flood season, it should advance vacating drainage to increase the amount of storage, increase river drainage and drainage speed, enhance the ca­pacity of flood discharge, and reduce the rising speed of the water level according to early warning and prediction of rain sit­uation, water situation and rainstorm.4.3 S cientific and rational layout to avoid rainstorm and flood disaster In the flooded or low-lying areas, it could heighten and reinforce river embankments, lay drainage pipe with large diameter, or conduct local relocation, to defend, ex-elude and relieve flood.4.4 Establish sponge c ity and enhance the a b ility of re­sponding to rainstorm and flood disaster It should estab­lish sponge city. Under the premise of ensuring urban drainage and flood prevention safety, it could realize the accumulation, penetration and purification of rain water in urban region to the maximum extent, and increase water seepage ground. By en­larging green land area, and constructing water seepage road and square, it makes rainwater seep into the ground, eases runoff velocity of ground rain water, reduces abrupt accumula­tion of rain water, promotes the utilization of rain water re­source and eco-environment protection. In construction process of sponge city, it should plan the systematic characteristic of natural rainfall, surface water and groundwater, coordinate each link of water recycling, and consider the complexity and long-term.4.5 Determine new and scien tific flood prevention and drainage standard, and build urban flood control embank­ment Urban flood prevention and drainage should use nation­al standard as basic guarantee. According to occurrence rule of flood disaster in the past 100 years, separate standard and specification could be compiled by combining specific situation of each city, and urban flood control embankment preventing rainstorm and flood should be built. It should notice the matc­hing of flood prevention and drainage standard, and properly improve flood drainage standard. The flood drainage standard has been made in some cities, such as 20-year flood drainage standard and random exclusion of 24-h rainstorm in Shanghai C ity；24-h rainstorm drainage standard in Heilongjiang Prov­ince, 10-year flood drainage standard in county-level city and 20-year flood drainage standard in city-level city.4.6 Enhance the supporting o f flood prevention and drainage fa cilitie s, perfect river way management, improve operation a b ility of the fa cility It should enrich urban flood control and drainage facilities, especially there should be ade­quate amount of flood drainage facilities to ensure that the city is not flooded. In the conditional place of old urban district, original rain and sewage combined pipe network should be changed into rain and sewage diversion system, and design ability of flood drainage pump station should be improved. De­sign scale of urban sewage treatment plant should consider the rain water amount from old urban district where rain and sew­age are difficult to separate. Old urban district has narrow road, and simple common ditch could be used to solve small underground pipeline layout space. Flood prevention and drain­age facilities must be built in the development of new urban dis­trict according to the related specifications and standards, to solve the flood problem outside and inside.4.7 Establish prediction and m onitoring system of urban flood prevention and drainage Urban flood disaster is often caused by short-time heavy rainfall or more process rainfall in low-lying area. In recent years, urbanization process of rapid development induces significance changes of urban hydrological characteristics：urban house buildings are dense, concrete coverage increases, rain water penetration decreases, and the function of rain water retention and regulation declines；the de­velopment of urban underground facilities is generally im­proved ,and diverse urban economy types and highly dense as­sets cause fragile urban comprehensive disaster tolerance, making that total amount of disaster loss under the equal haz­ardous conditions inevitably increases. Therefore, water con­servancy sector should joint with meteorological and hydrologi­cal departments to establish the prediction and monitoring sys- tem adapting to urban flood prevention and drainage.4.8 Enhance m eteorological and hydrological forecast and prediction Urban flood disaster is generated by local and regional heavy rainfall. It requires that meteorological depart­ment advances to accurately forecast climatic trend of heavy rainfall process. According to the prediction and forecast by meteorological department, hydrological department could ac­curately predict urban flood water level, to defend rainstorm and flood disaster.5 Conclusions and discussions(1) Rainstorm and flood disaster is one of natural disas­ters with the most serious loss in China, and government at all levels and each department should actively and jointly respond to and prevent it.(2) Rainstorm and flood disaster in each region all had common characteristics, with strong seasonal characteristics and ferocious intensity.(3) Rainstorm causing urban flood had large local intensity and regional unfixity.(4) The construction of sponge city could better respond to the occurrence of rainstorm and flood disaster.(5) Risk evaluation and zoning research of rainstorm and flood disaster were very favorable for making flood prevention countermeasure, which needed further research.(6) The establishment of prediction and monitoring system for urban flood prevention and drainage was an important work of defending rainstorm and flood disaster in Shaoyang City.References[1 ] GAO QH, MA ZJ, ZHANG YC, et al.Risk assessment of naturaldisasters [ M ]. 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Investigation and analysis of rainstorm and flood in Ningxia[J].Ningxia Journal of Agriculture and Forestry Science and Technology,2004(5) ：54 -56. (in Chinese).(T o page 82)lightning risk in Meizhou region roughly showed the trend of "center higher than around, south higher than north, and west higher than east".Seen from comparative analysis on risk zoning result and each factor, they had better corresponding relationship, illustra­ting that risk zoning method had certain rationality. Zoning re­sult reflected the relationship between lightning disaster risk and natural factor of lightning, fragility and vulnerability of disaster bearing bodies. For example, Meijiang District was in high risk area, and main causes were as below. On the one hand, its natural geography o f M surrounded by the mountains, and Mei­jiang River across the urban district" caused high lightning fre­quency. On the other hand, as central urban district of Meizhou City, it had more population, dense building and large econom­ic value. Natural lightning in Pingyuan, Jiaoling and Dapu was relatively less, adding relatively reduced population, building, economic value, it was low risk area of lightning. Above risk zoning result showed that assessment result tallied with actual situation, and evaluation method had certain scientificity.3 ConclusionsBy analyzing CG lightning density, lightning current intensi­ty, annual thunderstorm days, lightning disaster frequency, construction area per capita and GDP per capita in Meizhou re­gion during 1999 -2016, lightning risk zoning in Meizhou region was conducted, and results were as below.(1) Annual average CG lightning density in Meizhou re­gion showed the trend o f11 high in the center, low around, south higher than n orth", while average lightning current intensity had contrary distribution characteristic.(2)Lightning disaster risk in Meizhou region roughly showed the trend of 11 center higher than around, south higher than north, west higher than east". 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