Secondly, the geography of China has obvious differences between the north and the south. The interannual variation is usually expressed by the ratio of runoff variation coefficient (Cv) to the measured maximum and minimum annual average runoff. The region with the largest runoff variation coefficient in China is North China. The area with the smallest Cv value is the Yili River Basin in Xinjiang, which is controlled by the westerly belt all the year round. The Km value of the northern river with large Cv value is also large, and the Km value of the southern river with small Cv value is also small. The Km value of rivers with large catchment area is also smaller than that of rivers with small catchment area; The Km value of the main stream is less than that of the tributaries.
3. Under the influence of latitude, land and sea location and topography, the climate of China is from dry to wet from northwest to southeast, and from cold to hot from north to south. This distribution law of water and heat determines that the geochemical process of soil and weathering crust in China is gradually strengthened from northwest to southeast and from north to south. The Qinghai-Tibet Plateau and the northwest alpine region are strong uplift areas since Quaternary, and weathering and pedogenesis are in the initial stage. Broken weathering crust and young alpine soil developed. In the arid inland area of northwest China, the lack of water hinders the smooth progress of geochemical process. Soluble salts such as lime and gypsum are preserved in soil and weathering crust, forming saline weathering crust and saline dry soil. There is a little more rainfall in semi-arid areas, and the soil weathering crust has obvious calcification process, and carbonate weathering crust, grassland calcareous dry soil and semi-dry moist soft humus soil have developed.
4. The zonality law of horizontal distribution latitude of vegetation in China can be divided into two situations: east and west. The zonality of vegetation distribution in the eastern humid area has changed, forming vegetation zones with different latitudes from north to south. The cold temperate coniferous forest is located in the north of Daxing 'anling, with a large area of Larix gmelinii forest and sometimes mixed with Pinus sylvestris var. mongolica. Mongolian forest and temperate coniferous broad-leaved forest belt, including Changbai Mountain and Xiaoxing 'an Mountains. The deciduous and broad-leaved mixed forests such as Acer negundo and Tilia amurensis are distributed in humid habitats, while Mongolian oak forests are distributed in well-drained and sunny habitats, with occasional patches of Korean pine forests. However, Korean pine is mostly mixed with mixed forests, especially in the northern part of this zone. There are many kinds of oak forests in the deciduous broad-leaved forest in warm temperate zone. The transitional subtropics include evergreen broad-leaved forests, including Batai Mountain area and Huaiyang hilly area. It is dominated by evergreen oak forest, with wet trees in the east and drought-tolerant trees in the west. Subtropics is an evergreen fruit tree producing area in China, which mainly produces citrus, loquat and bayberry. Economic trees include tung trees and tea trees. South Asia tropical rain forest evergreen broad-leaved forest belt, latosol contains tropical trees such as Euphorbiaceae and Podocarpaceae. Tropical monsoon forest and rain forest belt in China are relatively small, and semi-evergreen monsoon forest is distributed in tropical open valleys or hilly latosol. Evergreen tree
To sum up, China has a vast territory with obvious differences between the north and the south. The zonal differences in the distribution of meteorology, climate, hydrology, soil and vegetation in China reflect the obvious differences between the north and the south.