Wind and hail disaster

Wind hail refers to disasters caused by strong convective weather such as hail, thunderstorm, strong wind and tornado. Due to the wide range of disasters, high frequency and heavy local area, the accumulated disaster losses are relatively serious, accounting for about 10% of the total natural disaster losses in China.

(2) Causes and characteristics

1. Reason

The wind and hail disaster is the product of strong thunderstorm clouds. In the mature stage of storm clouds, lightning and formation precipitation are generated. Due to the drag of precipitation such as rain or hail, downward airflow is generated in the cloud, which spreads around when it rushes to the ground, resulting in gust. The updraft in storm clouds can reach more than 60m/s, which can support hail particles with a diameter of 15 ~ 20mm or more. A tornado is a rotating funnel-shaped cloud that extends from the bottom of the storm cloud to the ground. When it reaches the ground, it will cause a strong whirlwind.

2. Features

1) has strong locality. Generally, the horizontal scale of strong thunderstorm clouds is about 10 km, and the life span is about several minutes to 1 hour. The horizontal scale of multicellular colony or zone is 10 ~ 100 km, and its life span can reach several hours to 10 hour. Generally, the width of disaster areas ranges from tens of meters to thousands of meters, and the length ranges from hundreds of meters to dozens or even dozens of kilometers.

2) Short duration. The wind and hail usually last 1 ~ 15 min, and a few last more than 30min.

3) The occurrence and development of strong thunderstorm clouds are influenced by cold (warm) fronts, eddies, shear lines and other weather systems, which can invade one after another with the movement of weather systems and cause disasters.

4) The occurrence time is concentrated, influenced by the ground thermal conditions, and mostly occurs from afternoon to midnight.

5) The frequency of occurrence is high, and wind and hail disasters are the most common meteorological disasters in China.

(3) Temporal and spatial distribution of wind and hail disasters

From a national perspective, the occurrence of wind and hail disasters is relatively concentrated in April-June. In South China (Guangdong, Guangxi, Qiong, Fujian and other places)1~1February, there were wind and hail disasters, accounting for about 60% of the total in March and April, and the disaster situation was also serious. The occurrence period of wind and hail disasters in the middle and lower reaches of the Yangtze River is from February to 10, and the peak period is from March to April. The wind and hail disasters in Yunnan-Guizhou-Sichuan area occurred from March to 10, and concentrated from March to May. The wind and hail disasters in the three northern regions (North China, Northwest China and Northeast China) mainly occur from May to September, with the highest peaks in North China and Northwest China from May to June, and the highest peaks in Inner Mongolia and Northeast China from June to July.

(d) Measures to mitigate wind and hail disasters

1) continuously improve the accuracy of wind and hail disaster prediction. With the improvement of science and technology, a storm weather monitoring network combining weather radar, meteorological satellite and ground monitoring has been established in various places, which greatly improves the forecasting level of severe weather caused by wind and hail and effectively reduces the losses caused by disasters.

2) Strengthen the division of wind and hail disasters. Wind and hail disasters have strong regionality and relatively fixed frequent areas. Dividing disaster-prone areas into key disaster prevention areas can take the initiative to prevent disasters.

3) Strengthen the artificial hail suppression test. Take artificial intervention measures to change the development process of storm clouds and weaken disaster-causing factors such as strong winds and hail. The main measures are: sowing silver iodide and other catalysts in the cloud, and using rockets to launch explosions to affect hail clouds.

4) Establish a reasonable structure of agriculture, forestry and animal husbandry in areas prone to wind and hail disasters. For example, increase forest coverage and arrange planting crops to avoid the windy and hail season.