Why doesn't it rain heavily in Yunnan?

Yunnan climate

I. Types

Yunnan is located in the low latitude plateau, with a special geographical position and complex terrain. Due to the influence of atmospheric circulation, winter is controlled by dry continental monsoon, and summer is dominated by humid maritime monsoon, which belongs to low latitude mountain monsoon climate. The climate types in the province are rich and diverse, including seven climate types: north tropical, south subtropical, middle subtropical, north subtropical, south temperate, middle temperate and plateau climate zone.

Second, the characteristics

The climate in Yunnan is characterized by low latitude climate, monsoon climate and mountain plain climate. Its main performance is:

(1) The regional differences and vertical changes of climate are very obvious, which are closely related to the latitude and altitude of Yunnan. From the latitude point of view, its location is only equivalent to the geographical latitude from Leizhou Peninsula to Fujian, Jiangxi, Hunan and Guizhou. However, due to the high terrain in the north and low terrain in the south, the height difference between north and south is 6663.6 meters, which greatly aggravates the temperature difference caused by latitude factors in the whole province. This combination of high latitude and high altitude, low latitude and low altitude is consistent, that is, the increase of latitude in the horizontal direction coincides with the increase of altitude in the vertical direction. On the one hand, the vertical temperature change in the whole province is 1 km, which is equivalent to the horizontal change of 1400 ~ 2500 km in the whole country; On the other hand, the temperature difference between eight latitudes in the horizontal direction of the whole province is equivalent to the annual average temperature difference between Hainan Island in the south of China and Changchun in the northeast, showing a variety of climates with hot, warm and cold zones. Except Jinsha River Valley and Yuanjiang River Valley, the annual average temperature in all places rises from north to south, averaging about 5 ~ 24℃, forming a general trend of high in the south and low in the north, and the temperature difference between north and south is about 65438 09℃. The starting and ending time of each season in different regions of the province can be more than 5 months different from the north and the south, and different regions have different seasons in the same period. For example, in April, central Yunnan is still warm in spring, southern Yunnan is already hot in summer, and northern Yunnan is still cold in winter.

Due to the influence of topography and different weather systems, the zonal distribution law of temperature in the whole province often appears special circumstances. These special circumstances also reflect the regional differences and vertical changes of climate. For example, it is hot in the north and cool in the south: Yuanmou in the north is hotter than JD.COM in the middle, and JD.COM is hotter than Jiangcheng in the south. Especially in the vertical distribution, due to the mountainous territory, the river bed is constantly eroded, forming a high mountain and deep valley. No matter in the north, middle and south, from the valley to the top of the mountain, there are differences in climate types caused by altitude rise. Generally, the temperature will drop by about 0.6℃ every time the height rises 100 meter. "One mountain is divided into four seasons, and ten miles is different from the sky", which is a portrayal of various climate types in Yunnan and shows the characteristics of "three-dimensional climate". The climate of "four seasons like spring, rain into winter" is mainly at the altitude of 1500 ~ 2000 meters.

(2) The annual temperature difference is small and the daily temperature difference is large. Because it is located in the low latitude plateau, the air is dry and thin. The amount of solar heat obtained in different places not only increases or decreases with the change of solar altitude angle, but also is influenced by clouds and rain. There are many rainy days in summer, the sun is covered by clouds, and the temperature is not high. The average temperature of the hottest day is about 19 ~ 22℃, which is lower than that of Beijing and Harbin. Winter is controlled by dry warm air flow, with sunny days, abundant sunshine and high temperature. The average temperature in Leng Yue is above 6 ~ 8℃. The annual temperature difference is generally 10 ~ 15℃, and the temperature is low in rainy days. Judging from the daily temperature change, it is cooler in the morning and evening and hotter at noon, especially in winter and spring, and the daily temperature difference can reach 12 ~ 20℃.

(3) The precipitation is abundant, with distinct wet and dry conditions and uneven distribution. The annual precipitation in most parts of the province is 1 100 mm, but due to the control and influence of different atmospheric circulation in winter and summer, the distribution of precipitation in seasons and regions is extremely uneven. 80 ~ 90% of the rainfall is concentrated in the rainy season of 5 ~ 10 every year, especially from June to August, accounting for about 60% of the annual rainfall. In the rainy season, there are often low temperatures and floods, which affect the growth and harvest of crops. The dry season is from June 165438+ 10 to April of the following year. At this time, the weather is sunny and warm, windy and dry, with little rain and snow. The precipitation only accounts for 10 ~ 20% of the whole year, or even less, so spring droughts often occur, affecting crop growth, and forest fires often occur this season. Precipitation is very uneven in geographical distribution. The annual precipitation in Jiangcheng, Jinping, Ximeng and other places can reach 2200 ~ 2700 mm, which is one of the rainy areas in China. People are often worried about too much rain. The least places, such as Binchuan, are only 584.1mm. People often look up at the sky and sigh that there is too little rain. Moreover, in a small area, due to the change of altitude, the precipitation distribution is uneven.

Yunnan has a long frost-free period. The southern border is frost-free all year round; The frost-free period of Wenshan, Mengzi, Simao, Lincang and Dehong in the south is 300 ~ 330 days. Kunming, Yuxi, Chuxiong and other places in the central region need about 250 days; The colder Zhaotong and Diqing can reach 2 10 ~ 220 days. Yunnan has good lighting conditions, 90 ~ 150 kcal per square centimeter per year, second only to Tibet, Qinghai, Inner Mongolia and other provinces and regions.

The advantage of this climate feature in Yunnan is that it is suitable for the growth of various crops, but the disadvantage is that the dry season and rainy season are too concentrated and the regional distribution is uneven, which is easy to cause disasters.