Geography composition (400 ~ 600 words) is urgent.

Distribution of disasters in Chongqing Meteorological disasters are the most common natural disasters, which have the greatest impact on people's lives, property and social development. Due to the influence of specific natural environment and atmospheric circulation, the weather in Chongqing is complex and changeable, and meteorological disasters occur frequently. Drought, flood, wind and hail, high temperature, cold damage, fog damage, snow disaster, debris flow and lightning disaster often occur. Especially drought, flood, wind and hail. Drought is the main meteorological disaster in Chongqing. Not only frequent, but also serious harm. There is a big drought every three years and a small drought every year. Drought is divided into spring drought, summer drought, summer drought, autumn drought and winter drought according to seasons. The frequency of spring drought in Chongqing is generally between10% and 30%, and it is higher in Tongnan, Rongchang, Dazu, Bishan, Yunyang, Wanzhou, Kaixian, Liangping and Zhongxian in the central and eastern parts, accounting for 40% to 50%. Youyang and Xiushan counties in the southeast are located outside the Sichuan Basin, and the spring rains are the earliest in the city, so the frequency of spring drought is the lowest, generally less than 10%. Summer drought is the most influential, with the frequency of 70% ~ 80%, and the frequency of severe summer drought is about 30%. Mainly occurred in the east and counties along the river. Summer drought is often accompanied by high temperature and heat, which not only seriously affects industrial and agricultural production, but also causes drinking water difficulties for people and livestock, and even an epidemic situation. The drought from mid-September to165438+1October is called autumn drought. It mainly affects the sowing of spring sowing crops. But it is beneficial to the growth of late autumn crops. The most harmful is the combination of autumn drought and summer drought, which often causes great losses to agricultural production. The drought from February 65438 to February of the following year is called winter drought. Rainstorms and floods are also frequent disasters in Chongqing. Heavy rain usually occurs in April ~ 10, the earliest in mid-March and the latest in mid-kloc-0/0. The most concentrated period is from late June to mid-July. In Wanzhou, Kaixian, Liangping and Yunyang areas in the northeast of Chongqing, due to the inter-valley flow in the Yangtze River basin, the frequency of rainstorm and flood is the highest, with an average of more than 7 times a year. The weather systems that produce heavy rain mainly include plateau vortex, southwest vortex (including basin vortex) and Jianghuai shear line. The rainstorm caused by southwest vortex is the strongest and most harmful. According to its causes, flood disasters can be divided into transit floods (floods caused by upstream rainstorms), local floods (floods caused by local rainstorms) and floods caused by a mixture of the two situations. Floods and mudslides caused by heavy rains are particularly harmful and often endanger people's lives and property. The loss caused by a rainstorm and flood can reach more than 654.38+0 billion yuan. Hail gale is another serious meteorological disaster in Chongqing, which is caused by small-scale weather system. The most common weather conditions are the gravity wave before the cold front and the hail line produced by the cold wave before the front. Its distribution is more in the mountains than in the plains, and less in the west than in the east. According to statistics, there are many hailstones in Qijiang and Fengjie, with an average of 3 times a year, and the longest hail in Fengjie can reach 9 times. Wanzhou, Wuxi, Jiangjin and Kaixian have an average of 2 ~ 3 times a year, Xiushan, Hechuan and Yongchuan have an average of 1 ~ 2 times a year, and other counties and cities have an average of 1 times. Hail in the city mostly occurs from February to 65438+ 10, with the most hail from mid-April to mid-May and mid-July to early August, accounting for more than 60% of the whole year. The maximum diameter of hail can reach 15 cm, and the maximum duration of hail can reach 60 minutes. Gale can be divided into cold wave gale and thunderstorm gale. Cold waves and strong winds mostly occur in spring and autumn, with the most in April, accounting for 66% of the total cold waves and strong winds. Thunderstorm and gale are mainly in summer, accounting for about 665,438+0% of gale days, which is the main form of gale. They mostly appear in the afternoon to midnight in summer, and last for a short time, but the wind is strong and destructive. The average windy day in the city is less than 4 days, mostly in Yamaguchi valley. Cold wave and freezing injury are weather processes in which strong cold air erupts southward on a large scale. The average number of cold waves in most districts and counties in the city is between 2 and 3 times a year, and there are 3 to 4 times in Wushan, Chengkou and Fengjie in the northeast, while the average number of strong cold waves in Yunyang, Wanzhou, Shizhu, Fengdu, Fuling, Kaixian and Liangping counties along the river is less than 2 times a year, and the number of strong cold waves is even less. This is related to the geographical location of Chongqing in Sichuan Basin, where cold air is not easy to invade. Freezing damage occurs frequently in Chengkou, Qianjiang, Youyang and Xiushan counties with higher terrain. Snowfall and freezing damage are similar in distribution. The average annual snowfall days in Qianjiang, Xiushan and other counties are above 10 days, while those in Chengkou and Youyang are above 20 days. However, there are not many disasters caused by snow. Cold damage and continuous rain mainly affect and endanger agricultural production. The first cold injury in Chongqing is the low temperature in spring, the temperature is mostly below 65438 02℃, the frequency of occurrence is 30% ~ 40%, and the time periods are mostly around the fright, vernal equinox and Tomb-Sweeping Day. In particular, the "late spring cold" around the vernal equinox and Tomb-Sweeping Day is the most serious, which often causes extensive damage such as rotten seeds and seedlings. Second, the frequency of low temperature in autumn is lower than that in spring. The occurrence time is mostly from late September of 10 to early October of 10, which is the main disaster affecting the yield of double-cropping late rice. Early frost often causes freezing damage to crops. There is also low temperature in summer, but the intensity is weak. Lightning disaster is a disaster directly caused by atmospheric lightning. Chongqing is one of the areas with the most thunder and lightning in China, which causes casualties and property losses every year. With the development of society, this kind of loss is becoming more and more serious. Therefore, lightning protection has been paid more and more attention. Lightning strikes may occur in Chongqing all year round, but mainly from April to 65438+ 10. Winter thunder is rare, with light intensity and harm. In addition, there are geological disasters, forest fires, crop diseases and insect pests caused by meteorological factors, which also occur in Chongqing. Among them, landslides and mudslides caused by heavy rains and floods are more common and have caused serious consequences. Forest fires often occur in the season of long sunshine and high temperature. Under suitable meteorological conditions, they are mostly caused by human factors or lightning strikes. Spontaneous combustion of trees is rare. Crop diseases and insect pests are mostly caused by hot and humid weather after warm winter, mainly wheat and rice.

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