What is the geographical environment of Yulin City?

Yulin City is located in the northernmost part of Shaanxi Province, bordering Gansu and Ningxia in the west, Inner Mongolia in the north, Shanxi across the Yellow River in the east and Yan 'an City in Shaanxi Province in the south. Geographical coordinates: 36 57 ′ ~ 39 35 ′ n,107 28 ′ ~11kloc-0/5 ′ e The administrative division of Yulin City is triangular. The easternmost part of Yulin is Duanzhai Village, Huangfu Township, Fugu County, the northernmost part is Liujiapo Village, Gucheng Township, Fugu County, the westernmost part is Liumaoyuan Township, Dingbian County, and the southernmost part is Tiejiao Town, Baimayao Township, Dingbian County. The maximum length from east to west is 309 kilometers, and the maximum width from north to south is 295 kilometers, with a total area of 43,578 square kilometers, accounting for about 2 1% of Shaanxi Province, ranking first among 10 prefecture-level cities in Shaanxi Province.

Yulin city belongs to the north-central part of Ordos platform of North China platform and depression of North Shaanxi platform in geological structure unit. The northeast is close to Dongsheng platform, which is an ancient platform. There is no magmatic rock formation and magmatic activity, and there are few earthquakes. The terrain is inclined from west to east, with an average elevation of 1600- 1800 m in the southwest and 1000- 1200 m in other places. The highest point is Wei Liang in the south of Dingbian, with an altitude of1907m, and the lowest point is the Qingjian Wuding River entering the Yellow River estuary, with an altitude of 560m.

Geomorphology can be divided into three categories: beach area, loess hilly and gully area and beam hilly area. Generally, it is bounded by the Great Wall, and the northern part is the sandy beach area on the southern edge of the Mu Us Desert, with an area of about 158 13 square kilometers, accounting for 36.7% of the area of Yulin City. The managed beaches are lush; Haizi (lakes) are dotted. The south is the hinterland of the Loess Plateau, with ravines and hills and ridges criss-crossing. Soil erosion has been initially controlled and the ecological environment has been greatly improved. The area is about 22,300 square kilometers, accounting for 5 1.75% of the area of Yulin city. Beam-shaped hilly areas are mainly distributed in the cradles of Wuding River, Dali River, Yanhe River and Luohe River in the southwestern mountainous areas of White. It covers an area of about 5,000 square kilometers, accounting for 1 1.55% of Yulin City. The high terrain, wide beam plateau, staggered beams and streams, and deep soil layers have gradually controlled soil erosion and contact.

Yulin City is one of the areas with high sunshine value in China. The sunshine hours in Shaanxi Province are the longest, with an average annual sunshine hours of 2593.5 ~ 29 14.4 hours, the highest in the northeast and the lowest in the south. There is more sunshine in May-August in a year, and less sunshine in 12- February of the following year. The average sunshine percentage is 59 ~ 66%, and there is little difference in Yulin. It is the largest in winter (12 ~ 65438+ the following year 10 month), and gradually decreases from spring to summer to the minimum in late summer and early autumn (July-September), and increases rapidly from Mid-Autumn Festival to winter.

The temperature in the four seasons is obvious, the temperature in spring is higher than that in autumn, the temperature in spring is fast and unstable, and the temperature in autumn is fast. Winter is controlled by the cold air mass in the north, with high air pressure, clear weather and high clouds. In winter, the average temperature is -7.8 ~ 4. 1℃, and the temperature change gradient is large, and the gradient direction is from southeast to northwest. 65438+1frozen from the end of October to the beginning of April of the following year. In general, the depth of frozen soil is 1 ~ 1.2m, and the temperature rises obviously after spring, with an average daily temperature increase of about 0.2℃. However, due to the continuous southward invasion of Siberian polar dry and cold air mass, the temperature in spring is very unstable, and sudden snowfall may occur in some areas in mid-May. In summer, affected by continental air mass and subtropical high, the temperature is high and the weather is hot. The average monthly temperature is above 20℃, and the average number of days with the highest daily temperature ≥30℃ is 22 ~ 68 days. The temperature gradient is small, and the gradient direction is from near east to west; In autumn, under the attack and stable control of polar air mass, the temperature drops rapidly, especially in June10 ~165438+10, with an average daily temperature drop of 0.27℃.

There are 53 rivers flowing into the Yellow River in Yulin City, all of which are short and small. The larger rivers are mainly four rivers in Sichuan: Huangfuchuan, Qingshuichuan, Gushanchuan, Shimachuan, Kuyehe, Tuwei, Jia Luhe and Wuding. The rivers that flow into the Yellow River are based on the erosion of the Yellow River, and the flow direction is from northwest to southeast (the upstream flow direction of the Wuding River is three folds), and the tributaries are dendritic, increasing from downstream to upstream. The lower reaches of larger rivers are bedrock canyons with large slopes and few short straight tributaries. The valley in the middle reaches is generally wide, the floodplain terraces are developed, the rivers are wide and shallow, and the larger tributaries are mostly concentrated in the middle reaches. The upper reaches are mostly developed in ancient river valleys and streams, and rivers form loess canyons (some of the bottoms cut into bedrock), with large slopes and many outposts. The flow direction is controlled by the direction of valleys and streams in ancient topography, and there are many tributaries, but they are generally straight. ?