Why is there such a big difference between the banks of Huaihe River?

North of Huaihe River is warm temperate zone, south of Huaihe River is subtropical zone, and the climate on both sides of Huaihe River is quite different.

In fact, the first is the climate dividing line. As far as the hot zone is concerned, it is the dividing line between the northern warm temperate zone and the southern subtropical zone;

In the division of water, it is the dividing line between the arid and semi-humid climate in the north and the humid climate in the south;

In the division of rainy season and dry season, it is the dividing line between spring drought and summer rain climate in the north and spring rain, plum rain and summer drought climate in the south.

In fact, the most fundamental reason is the subtropical high (the most important weather indicator affecting summer in China: in hot and rainy summer, the subtropical high pushes northward and meets the rain brought by local cold air, bringing high temperature). The northernmost edge it can reach is the Qinling Mountains and the Huaihe River, and it has gradually retreated to the south. ......

Climate dividing line ① The average temperature in June 5438+1October north of Qinling Huaihe River Line was below 0℃, and in June 5438+1October south of Qinling Huaihe River Line was above 0℃; ② The annual precipitation in the north is below 800 mm, and that in the south is above 800 mm; ③ The temperature zone in the north belongs to warm temperate zone, while the temperature zone in the south belongs to subtropical zone; ④ The northern part belongs to semi-humid area and the southern part belongs to humid area.

The dividing line of river hydrological characteristics is in the north of Huaihe River in Qinling Mountains-small water volume, short flood season, large sediment concentration and ice age; South of Huaihe River in Qinling Mountains-large amount of water, long flood season, small sediment concentration and no ice age.

The dividing line of soil types is fertile cinnamon soil (yellow soil) north of Huaihe River in Qinling Mountains. There are many barren red soils south of Huaihe River in Qinling Mountains.

The boundary of natural vegetation types is temperate deciduous broad-leaved forest north of Huaihe River in Qinling Mountains. South of Huaihe River in Qinling Mountains-subtropical evergreen broad-leaved forest.

The dividing line of agricultural production is in the north of Huaihe River in Qinling Mountains-the farming system is three crops every two years or one crop every year, the cultivated land is mainly dry land, and the main crops are wheat, corn, cotton and peanuts; South of Huaihe River in Qinling Mountains-The farming system is two or three crops a year, with paddy fields as the main cultivated land and rice, wheat, cotton and rape as the main crops.

However, this transition and change is completed through a fairly wide belt. We can't see any changes in climate, agriculture, natural landscape, etc. on both sides of the Huaihe River, which are more than ten or twenty kilometers apart. In fact, because the Huaihe River area is mainly a plain area, the cold and warm air flow between the north and the south is unimpeded, and it is really impossible to produce a clear north-south dividing line. Take "orange crossing Huaihe River, turning north into bitter orange" as an example. Due to the strong cold air in the central and southern parts of eastern China in winter, it often brings fatal low temperature to citrus. Therefore, even on the banks of the Yangtze River south of Huaihe River, except for some favorable areas, citrus cultivation generally has no economic value.

The Qinling Mountains to the west of the north-south boundary block the cold air in the north in winter, so Lingnan is a typical subtropical zone (it can grow citrus and other subtropical index plants that can't grow on both sides of Huaihe River at the same latitude) when it is a typical warm temperate zone to the north of the ridge. However, the Qinling boundary is not a line. Because the southern slope of Qinling Mountain is subtropical only at an altitude of 1000 meters, and the width between the contour lines of the two slopes of Qinling Mountain, that is, the width of the boundary zone, is about 90- 1 10 km. Moreover, in history, the north-south boundary zone moved north and south with climate change. If global warming continues, the subtropical northern boundary may even move northward to the middle and lower reaches of the Yellow River in the future.