Physical geography of Pucheng county

The general feature of Pucheng landform is mountainous, surrounded by mountains on three sides: north, east and west. The south-central part is flat and wide, and the terrain drops from north to south; Nanpuxi runs through the north and south, the surface runoff is dendritic, the basin is beaded, and the chalk mouth is prominent. The intersection of the two mountains and the watershed of the two water systems are the low hills from Xianyang to Fengling in the north, the junction of Wuyishan and Xianxialing in southwest Zhejiang, the watershed between Qiantang River and Minjiang River, and the watershed between Minjiang River and Poyang Lake. Poyang Lake water system is a tributary of the Yangtze River, so it is also a watershed between the Yangtze River water system and the Minjiang River water system.

The stepped terrain is obvious: from the middle of the county to the east and west edges, there are four landforms: valley basin, hills, low mountains and Zhongshan, with obvious height difference and distinct levels. The formation of this stepped terrain is mainly controlled by lithology except for structural reasons. Granite in the central part of the county has coarse crystals, different weathering forces of internal minerals, developed joints and fissures, and is easy to be weathered and eroded, which has become the main distribution area of valley basins and hills. The volcanic rocks of Nanyuan Formation in the east-west margin are mainly tuff lava with different degrees of silicification. The lithology is dense and hard, and it is not easy to weather. In its distribution area, most of the middle mountains and some low mountains are developed. Quartz schist in metamorphic rocks of Jian 'ou Group and sand shale of Lishan Group. , with hardness and wind resistance between granite and volcanic rock series of Nanyuan Group, has become the main lithology of low mountains.

Beaded basins are scattered all over: the county belongs to Pucheng basin, with valleys and basins arranged alternately, and beaded basins scattered all over the mountains. The main stream Nanpuxi is connected in series 10 valley basins, including Zhongxin, Xianyang, Xunling, Guancuo, Nanpu, Fuling, Li Antang, Linjiang, Yongxing and Shibei, with an area of 4,000-6,000 mu. Small basins of nearly a thousand acres and hundreds of acres are scattered among mountains, and tributaries meander in the basins.

The terrain of chalk mouth is prominent: there are many chalk mouths in the middle mountain area at the junction of Zhejiang and Jiangxi, and in the vertical or oblique mountainous area. Some were formed by fault collapse, and some were ancient estuaries. These chalk holes were called "passes" in ancient times. It is the traffic artery and military hub of Fujian, Jiangxi, Fujian and Zhejiang. The famous ones are Erduguan and Muchengguan in the northwest of Panjin. These chalk holes are also the channels for cold air from the north to invade Pucheng and even the hinterland of Fujian. Pucheng County is located at the junction of seven counties (cities) in Fujian, Zhejiang and Jiangxi provinces, and is known as the "North Gate of Fujian". Pucheng is located at the junction of maritime climate and continental climate, close to continental climate, and is a typical subtropical monsoon humid climate zone. The climate in the region has four distinct seasons, moderate temperature, abundant rainfall, abundant heat resources, obvious dry and wet seasons, and synchronous rain and heat; The annual average temperature is 17.4℃, the annual rainfall is about 1700mm, the annual sunshine hours are 1900 hours, and the frost-free period is about 254 days. Due to the instability of monsoon climate and complex terrain, disastrous climate frequently occurs, such as high temperature heat damage, low temperature cold damage, drought, flood, ice disaster, wind disaster and so on.

spring

Generally, it starts from March 1 every year and ends on May 20th every year, totaling 8 1 day. (If the year and place are not specified, the value is the average of 195 1~ 1980 in Nanpu Town or Chengguan District. The precipitation accounts for about 30% of the whole year, and the sunshine percentage is 30%. The temperature rises gradually, but fluctuates greatly, with late spring cold in 45% years. Generally speaking, before March 15, the daily average temperature was lower than 12℃, and the temperature generally rose around March 18, and it was in a low temperature process around March 25th, and it rose again at the end of March, and "Qingming Cold" appeared around April 2nd.

summer

Generally, it starts from May 2 1 and ends on September 25, lasting 128 days. About 50 days after long summer is the rainy season, and there are often 2~3 rainstorms, which often

Flood disaster. The rainfall from May to June reached 660.6 mm, accounting for 37% of the annual rainfall. From July to August, it entered sunny, hot and hot weather, with an average of 25 days when the highest temperature was above 35℃, and the extreme maximum temperature reached 40.8℃. The rainfall from July to September is 358.7mm, accounting for 20% of the annual rainfall, with extremely uneven distribution, mainly affected by typhoons. 87% of the years are dry, and 23% of the years are severely dry for more than 36 days.

autumn

Generally, it starts from September 26th and ends at1October 30th 165438, lasting 66 days, from hot period to cold period. "The Millennium is divided into autumn nights, and it is cool all night." The rainfall is relatively small, with the monthly rainfall of 10 ~ 1 1.8 mm, accounting for 6% of the annual rainfall. It takes about 10% years to have "continuous autumn rain".

winter

Generally, it starts from 65438+February 1 and ends on February 28th of the following year, which lasts for 90 days. The climate is dry and cold. It is attacked by cold waves twice a year, with an average temperature of 6.2℃ in 65438+ 10, with an extreme minimum of -8.0℃. 1 month, the average relative humidity is 77%, and the extremely low value is 58%. The average first frost date is 165438+ 10 16, and the average final frost date is March 6th. The average annual frost lasts for 32 days, up to 54 days, and the longest continuous frost lasts for 26 days. There are 27.5 days of freezing every year on average, and the continuous freezing has reached 19 days. The average annual snowfall is 7.4 days, the longest continuous snowfall is 7 days, and the deepest snow has reached 28 cm. There has been fog and rain.

In a year, Pucheng's climate has four obvious characteristics.

At the same time of rain and heat, 10℃ was taken as the germination temperature of thermophilic plants, and the accumulated active temperature of 10℃ or more in a year was 5443.6℃, lasting for 250 days. During the same period, rainfall 14 14.6 mm, sunshine 1438.5 hours, and rain and heat match.

Four distinct seasons, abundant rainfall and sunshine. Annual rainfall1780.2mm, annual average temperature 17.4℃, sunshine1893.5h.. Spring and autumn are slightly shorter, summer is the longest, and the four seasons are distinct.

Three-dimensional climate is remarkable: Pucheng terrain is relatively high and low, forming a three-dimensional climate in China. Generally, for every elevation increase of 100 m, the warm period in spring is delayed by 3 days, and the influence date of the first cold air in autumn is advanced by 4 days. The active accumulated temperature greater than or equal to 10℃ decreases 188.9℃, the annual rainfall increases by 72.5 mm, and the frost-free period decreases by 3 days. The above trends are slightly different on different sides of the ridge.

The influence of monsoon is remarkable: Pucheng is a typical monsoon region, with northerly winds prevailing in winter and southerly winds prevailing in summer. As a result, Pucheng has both severe cold and intense heat, with a large daily variation (February 0+February 9, 24.2℃ 19565438+65438). Monsoon also affects the distribution of monthly rainfall. In a year, most of the precipitation is concentrated in the first half of the year, with the most in April-June. In the second half of the year, there is little rainfall and it is often dry. Pucheng's water resources are supplemented by precipitation. The annual average runoff depth is 104 1 mm, and the annual average runoff is 31.210.30 billion cubic meters (4,654 million cubic meters in wet years, 2,988.9 million cubic meters in normal years and 2,300 million cubic meters in dry years).

The uneven distribution of precipitation during the year causes obvious seasonal changes in monthly discharge and water level. The annual runoff from April to June accounts for 58. 1%, from April to September (flood season) accounts for 78.2%, and from April to July accounts for 69.2%.

According to the measured data of Wan 'an Hydrological Station 1956~ 1968, the annual average surface evaporation of Pucheng is 993.5mm ... According to the contour map of the annual average surface evaporation of provincial hydrological station, the annual average surface evaporation of Pucheng is 700~750 mm, and according to the underground hydrological station1971~/.

The average water yield per square kilometer for many years is 6.5438+0.0407 million cubic meters, the per capita water consumption is 965.438+0.52.48 cubic meters, and the average water consumption per mu of cultivated land is 57.3 1 cubic meter.