Subtropical climate distribution in China

China's subtropical climate zone is located between 25 and 35 north latitude, and it is divided according to the climate of planetary wind system. It is an arid area controlled by subtropical high. However, due to the difference between land and sea and the change of temperature and pressure field caused by the uplift of the Qinghai-Tibet Plateau, the monsoon circulation changed the circulation system of the near-surface planetary wind system, changed the arid continental climate into a humid subtropical monsoon climate, and changed the arid desert landscape into a humid evergreen broad-leaved forest landscape. After thousands of years of human activities, this area has become a densely populated and economically developed area in China. The average annual precipitation in this area is generally 800 mm~ 1600 mm, which is 1~2 times more than that in North China and richer than that in Southwest China. The distribution of precipitation decreases from southeast to northwest. The annual precipitation in hilly areas of Zhejiang Province is 1200mm ~ 180mm, that in Nanling mountain area and hilly areas of the south of the Yangtze River is about 1500 mm, and that in the middle and lower reaches of the Yangtze River is about1200mm. The influence of topography on precipitation is also remarkable. Generally, there are more mountains than flat land, and there are more windward slopes than leeward slopes. For example, Tunxi in Anhui is very close to Huangshan, and the precipitation in Huangshan is 700 mm more than that in Tunxi (Tunxi 1507.8 mm, Huangshan is 2263.9 mm). The annual precipitation of Luoxiao Mountain and Xuefeng Mountain can exceed 1800 mm.

Summer rain is the most, followed by spring rain, autumn rain is worse, and winter rain is the least, but winter rainfall can also account for more than 10% of the annual precipitation. The middle and lower reaches of the Yangtze River are areas with high proportion of winter rain and abundant spring rain in China. This seasonal distribution of precipitation is closely related to the geographical location of the middle and lower reaches of the Yangtze River and the atmospheric circulation process.

The middle and lower reaches of the Yangtze River lie in the east of the Qinghai-Tibet Plateau. In winter, the north-south jet of the westerly belt meets over this area, forming a relatively stable shear line. Coupled with the influence of Nanling Mountains, a relatively durable quasi-static front in South China appeared on the ground, with frequent cyclones and extremely rainy weather. In most areas, the average precipitation in 65438+February and 65438+1October is about 40 mm~50 mm, and it is 60 mm in February. Since March, the warm and humid air flow in the south has strengthened and the precipitation frequency has increased. In late March, Gannan first entered the spring rain period, and the spring rain gradually extended to the northwest, southwest and northeast. In most areas, the spring rain doesn't end until early and middle June. There is a lot of precipitation and a long rainy period in the hilly areas of the south of the Yangtze River. In most areas, the spring rain begins in early April and ends in late May, and the rainy season lasts for 60 days. There are more spring rains in this area, and the proportion of spring rains in Changsha and Nanchang is about 40%, which is more than summer rain. In Nanjing, Shanghai, Wenzhou and other places, spring rain accounts for about 25% of the annual precipitation.