Meteorology in the study area

The climate types in northern China are complex, from the cold and sub-cold regions of the Qinghai-Tibet Plateau in the southwest to the middle and warm temperate regions in the northwest and north China, and then to the cold temperate regions in the Daxinganling region in the northeast, spanning multiple climatic zones. Combined with the physical geography and climatic conditions in northern China, it can be divided into three climatic zones: the alpine climate zone on the Qinghai-Tibet Plateau, the continental climate zone in northwest China and the monsoon climate zone in east China.

First, the Qinghai-Tibet Plateau alpine climate zone.

It mainly includes the Qinghai-Tibet Plateau, Kunlun Mountain and Tianshan Mountain. Due to its own geographical conditions, the climate temperature in this area is low, the annual temperature difference is small, the daily temperature difference is large, and the solar radiation and vertical zoning are obvious. Half of the Qinghai-Tibet Plateau has an annual average temperature below 0℃, while other areas such as Yarlung Zangbo River, Hemangu and Qaidam Basin are relatively warm, with an annual average temperature of 3 ~ 5℃. The temperature in Qinghai-Tibet Plateau changes obviously with altitude, but it varies from place to place. Generally, the temperature drops by 0.4 ~ 1.20℃ every time it rises 100 m. The Qinghai-Tibet Plateau is high in altitude, the air is thin and clean, and the atmospheric distance through which solar radiation passes is short, so the solar radiation is less weakened. The total solar radiation is the highest in China, with an annual total of 4,000-7,000 MJ/m2, which is 2,000-3,000 MJ/m2 larger than that in the eastern part of the same latitude. The geographical distribution of precipitation in Qinghai-Tibet Plateau is uneven. From more than 4,000 mm in the southeast of Tibet to Lenghu Lake in the northwest of Qaidam Basin, the annual average precipitation is gradually decreasing. The precipitation in the cold lake is only 17.6mm, and the maximum precipitation is about 200 times of the minimum precipitation.

Second, the northwest continental climate zone

Northwest arid region can be further divided into warm temperate continental climate subregion and middle temperate continental climate subregion, and each subregion can be further divided according to the degree of wetness. Northwest arid areas mainly include Tarim Basin, Junggar Basin, Hexi Corridor, Inner Mongolia Plateau and some loess plateaus. It is a typical continental arid and semi-arid climate environment, with less precipitation, large evaporation, large temperature difference between day and night, large sandstorm in spring and extremely cold and dry in winter. The precipitation in the arid area of northwest China decreases from southeast to northwest, and from mountainous area to plain. Due to the climatic conditions formed by special geographical location, precipitation is mainly concentrated in high mountain areas, such as Qinling Mountains, Qilian Mountains, Altai Mountains and Kunlun Mountains. The average annual precipitation is mostly 600 ~ 800 mm, which is called "wet island" in arid areas. The central part of the basin is extremely dry and lacks rain, and the precipitation is generally less than 50 mm, which gradually decreases from the piedmont to the central part of the plain. The evaporation in northwest China is large and the relative humidity is small. The annual evaporation in most areas is above 1500 ~ 2000 mm, and the regional distribution of annual evaporation is opposite to precipitation. The temperature in northwest China varies greatly. The areas with annual average temperature below 0℃ are distributed in the vast Altai Mountain, Tianshan Mountain, Karakorum Mountain, Qilian Mountain and Pamir Plateau, and the annual average temperature in the basin is generally 0 ~ 10℃. It is characterized by high temperature in summer, severe cold in winter, and large annual and daily temperature differences. The northwest wind is strong, mainly northwest wind, mainly northeast wind in southern Xinjiang; The number of windy days above Grade 8 is 50 ~ 75 days.

Third, the eastern monsoon climate zone.

The monsoon climate zone in the eastern part of northern China mainly includes Huanghuaihai region, Guanzhong basin, Northeast Plain and its eastern coastal areas. The climate has obvious seasonal variation, which is influenced by the alternation of winter and summer monsoon. Summer is hot and rainy, and winter is cold and rainy. Huanghuaihai belongs to the semi-arid monsoon climate subregion of warm temperate zone, and the average annual precipitation is generally 500 ~ 600 mm; There is a lot of precipitation in coastal areas, about 600 ~ 650 mm. Xinji, Nangong and Hengshui areas in Jizhong Plain are affected by the sinking of Mount Tai and Yimeng Mountain and the northward airflow, and the precipitation is reduced, with an average precipitation of less than 500mm for many years, which is a low-value precipitation area in the plain area. The precipitation is unevenly distributed during the year, and 80% of the precipitation in the whole year is concentrated in the flood season from June to September, which is often dry in spring and waterlogged in autumn. Precipitation changes greatly every year. In most areas, the precipitation is less than 400 mm in rainy years and more than 800 mm in rainy years. The annual average temperature is 10 ~ 15℃, and the annual temperature difference is large. The annual minimum temperature is-1.8 ~ 1.0℃, and the maximum temperature is above 40℃. The water surface evaporation is 900 ~ 1400 mm, and1~ is relatively stable in February, and gradually increases in March, obviously increases in April ~ May, reaches the maximum in June ~ September, and begins to decline after 10.

The northeast monsoon climate zone mainly includes the northeast plain (Songnen Plain, Liaohe Plain and Sanjiang Plain) and the eastern coastal areas, belonging to the humid and semi-humid monsoon climate subregion in the middle temperate zone, with long and cold winter, strong wind in spring and short and warm and humid summer. The annual average temperature is -5 ~ 10℃, and the temperature difference between north and south is as high as 15℃, and the temperature changes greatly during the year. Winter lasts for 6 ~ 7 months, the monthly average temperature is -6 ~ 30℃, summer is short, and the average temperature in July is around 20℃. The annual precipitation is 400 ~ 1000 mm, which varies greatly among regions. There is a lot of precipitation in mountainous areas, generally 600 ~1000 mm; There are few plains, generally 400 ~ 600 mm, northwest winds and north winds prevail in Nenjiang Plain and the northern section of Xiaoxing 'anling Mountain, and southwest winds and south winds prevail in Songhua River Basin, with relatively high wind speed. Guanzhong basin belongs to the sub-region of warm temperate semi-humid monsoon climate, with four distinct seasons, hot and rainy in summer, cold and rainy in winter, and rainy in spring and autumn. Annual average temperature 10 ~ 15℃, annual extreme maximum temperature 35 ~ 42℃, minimum temperature-10 ~- 16℃. The annual rainfall is 540 ~ 750 mm, mostly concentrated in July ~ September, and the relative humidity is 72%.