Characteristics of natural disasters in my country,

Our country has a vast territory. Its northwest is located in the hinterland of Eurasia, the largest continent in the world, its southeast is adjacent to the largest water surface in the world, the Pacific Ocean, and its southwest is the highest plateau in the world, the Qinghai-Tibet Plateau. Such extremely complex geographical conditions make my country's climate characterized by strong monsoon, continental and type diversity. Compared with other countries at the same latitude in the world, this characteristic of our country's climate is very unique.

Monsoon climate is significant

my country is located in the southeast of Eurasia. Facing the vast ocean, the huge thermal difference between the sea and the land makes the characteristics of my country's monsoon climate more obvious. The main manifestations are significant changes in the prevailing wind direction in winter and summer, and significant seasonal changes in precipitation as the monsoon advances and retreats.

In winter, mainland my country is mainly controlled by polar continental air masses or modified polar continental air masses. There are mostly high-pressure ridges at high altitudes between 80 and 90°E, while high altitudes along the coast are often large troughs. The cold air continues to move southward, strengthening the cold high pressure on the ground (Mongolian high pressure), and the warm ocean is mostly controlled by low pressure. Airflow continuously flows from high pressure areas to low pressure areas, causing northwest, north and northeasterly winds to prevail in the lower troposphere in winter in my country. The cold high pressure on the polar continent and its accompanying polar front or sub-cold front are the main control system of my country's weather in winter. The weather and climate are characterized by low precipitation, low temperature and dryness. In particular, cold waves or strong cold air weather processes last for a long time and have a wide range of impacts. The accompanying strong winds and cooling are very harmful to industrial and agricultural production.

In summer, most of mainland my country is controlled by tropical and subtropical oceanic air masses and tropical continental air masses. There is a low-pressure trough in the upper air at 70-80°E, a shallow ridge along the coast, and a surface pressure system. The Eurasian continent is dominated by the Mongolian low pressure, which, in conjunction with the high pressure over the ocean, causes southwesterly, southerly and southeasterly winds to prevail in the lower troposphere in my country in summer. At this time, in addition to the polar cold air and its accompanying cold fronts that can still affect North China, continental thermal low pressure, subtropical high pressure, tropical low pressure, tropical cyclones, easterly waves, etc. have become the main systems affecting my country's weather. The weather and climate are characterized by high temperature, humidity and rain. This climate characteristic of rainy and hot weather in the same season provides good conditions for agricultural production in my country. High temperatures combined with heavy rainfall have made my country the main rice producing area in the world. Rice cultivation in my country can reach as far north as Mohe in Heilongjiang Province, and from a small area in the northeast to One crop per year, three crops per year in North and Central China, two crops per year, and three crops per year in South China all benefit from the climate characteristics of rain and heat in the same season. However, continuous heavy rains or local heavy rainfall often cause large-scale or severe local floods in summer in my country. The violent winds and rains carried by tropical cyclones have a great impact on fishery production and maritime transportation, and even cause losses of life and property. Wind disasters and floods are often caused near the landing site (sometimes deep inland).

The arrival of the summer monsoon is marked by a sudden increase in rainfall. Generally, the summer wind and rain belt appears in the northern part of the South China Sea in early May and moves to the coast of South China in mid-May. Then, it slowly pushed northward and stagnated in southern China in late May. It suddenly pushes northward in early June and reaches the middle and lower reaches of the Yangtze River in mid-June. This is the beginning of the Meiyu period. The plum rain generally lasts until early July. Then, the summer monsoon affects the area north of the Huaihe River, and North China and Northeast China enter the peak of the annual rainy season in late July, which lasts until early August. Starting from mid-to-late August, the summer monsoon rain belt quickly retreated southward, and rainfall decreased rapidly across the country (except for the southeastern coastal areas affected by tropical cyclones). From mid-September to early October, it stagnated in the central and eastern areas of the Yangtze River and Huaihe River, forming a relatively rainy belt. Due to the influence of topography, Western China often experiences continuous autumn rains and is also a relatively rainy area. In September and October, northern China and central China mostly experience crisp autumn weather. In mid-October, the rainband retreated to southern China. Whether the start and retreat times of the rainy season in various parts of my country are normal or not are directly related to the advance and retreat times of the summer monsoon.

Interannual differences in the onset, retreat and maintenance time of the summer monsoon determine my country’s interannual summer precipitation conditions and the distribution of drought and flood areas. Statistics show that in years when the summer monsoon is strong, the rain belts quickly push to the north. It is rainy in the north. The plum rain period in the middle and lower reaches of the Yangtze River is short, and severe drought occurs. On the contrary, the rain belts in the middle and lower reaches of the Yangtze River are stagnant, with excessive rainfall and floods. Drought appears in the north, such as in 1999. Therefore, the characteristics of the monsoon climate, especially the abnormal changes in winter and summer monsoons, make my country one of the countries with the most frequent meteorological disasters in the world. Drought, heavy rains, floods, low temperature and cold damage are the main meteorological disasters in my country. According to statistics from 1950 to 1999, the average area affected by disasters such as drought, wind, hail, and low temperature frost in my country is more than 38 million hectares every year.

Look at my country’s climate type based on the classification of heat indicators

my country is located in the southeast of Eurasia, the largest landmass in the world, facing the Pacific Ocean, the largest ocean in the world, with complex terrain , a vast territory. It starts from the Altun Mountain in the west and ends at the Ussuri River in the east, spanning 63 longitudes. It starts from Mohe in the north and ends at Zengmu Shoal in the South China Sea. The latitude difference between north and south is 49 degrees. Therefore, my country's climate is very complex and diverse. From a thermal perspective, our country spans the equatorial zone, tropics, subtropics, temperate zones, mountains, plateaus and cold climates from south to north. 87% of the country's land area is temperate, subtropical and tropical.

China is located in the east of Asia, on the west coast of the Pacific Ocean. The territory starts from Zengmu Shoal (near 4° north latitude) in the south to Heilongjiang Shang near Mohe (more than 55° north latitude), with a distance of about 5,500 kilometers from north to south; from the Pamir Plateau (near 73° east longitude) in the west to Heilongjiang and Uzbekistan in the east The confluence of the Suli River (more than 135° east longitude) is about 5,000 kilometers apart from east to west. The land area is about 9.6 million square kilometers, the eastern and southern continental coastlines are more than 18,000 kilometers, and the water area of ​​inland seas and coastal seas is about more than 4.7 million square kilometers. China borders 14 countries and 8 countries by sea: it borders North Korea in the northeast, Russia, Kazakhstan, Kyrgyzstan, and Tajikistan in the northeast and northwest, Mongolia in the north, Afghanistan and Pakistan in the west, and Afghanistan and Pakistan in the southwest. It borders India, Nepal, and Bhutan, and to the south are Myanmar, Laos, and Vietnam.

1) There are many types, covering almost all types of natural disasters in the world. Among various types of disasters, floods, droughts and earthquakes are the most harmful.

(2) Disasters occur with high frequency, intensity, and severe losses. There is a saying in my country that "famine occurs at the age of three, decline occurs at the age of six, and famine occurs at the age of twelve." According to historical statistics, in the 2155 years from 206 BC to 1949, there were 1029 floods and 1056 major droughts in Japan. Floods and droughts occurred almost every year, and disasters that disabled more than 10,000 people occurred every 10 to 20 years. Appear once. In the past 40 years, there have been an average of 75 droughts, 5.8 floods, 6.9 typhoons, and 2.5 freezing disasters every year, all far exceeding the world's average frequency. In the past 40 years, the area affected by crop disasters in a typical year ranged from 40 million to 47 million hectares, with a population affected by disasters of approximately 200 million, the number of deaths due to various natural disasters ranging from 1,000 to 10,000, and direct economic losses of more than 50 billion yuan. In the four years from 1989 to 1992, the average annual loss was about 1/4 of the global average annual loss of US$50 billion in the early 1990s.

(3) The spatial and temporal distribution is wide, and the geographical combination of disasters is obvious. The spatial distribution and regional combination of natural disasters in my country are strongly related to regional differences in natural and socioeconomic environments. In terms of macroscopic distribution, droughts that mostly occur in spring and autumn are mainly distributed in the northwest, the Loess Plateau and North China; heavy rains and floods that mostly occur in summer are mainly distributed in the vast eastern monsoon area, concentrated in the seven major rivers watershed; forest fires are mainly distributed in the northeast and southwest forest areas, mostly occurring in the winter and spring dry seasons; earthquakes are mainly distributed in the active tectonic belts of the southwest, northwest and north China; low-temperature freezing damage and ice and snow disasters are particularly prominent in the Qinghai-Tibet high cold current area; typhoons , Storm surges mostly occur in the southeastern coastal areas. In the southwest, earthquakes and heavy rains caused clusters of landslides, collapses, mudslides, and flash floods. The spatial distribution of natural disasters also shows a certain degree of yoke. For example, changes in the strength of monsoons lead to floods in the south and drought in the north, or drought in the south and floods in the north, as well as the phenomenon of floods first and then drought or first drought and then floods in an area. According to statistics from the National Meteorological Administration, the average frequency of various meteorological disasters has shown an increasing trend. It was 19.56 times in the 1950s, 26.20 times in the 1960s, and 28.18 times in the 1980s.