1. Geological conditions
Chongqing has developed sedimentary strata, complex geological structure and rich mineral resources. The basement is composed of pre-Sinian shallow metamorphic sandstone and slate, and the pre-Sinian metamorphic rock series is partially exposed in Xiushan and Youyang. Above the basement, it is covered by metamorphic strata from Sinian to Quaternary. Jurassic strata dominated by red clastic rocks are the most developed and widely distributed; Lower Paleozoic strata are mainly sulfate rocks such as dolomite and limestone, which are mainly distributed in the southeast of the city. Magmatic rocks are basic rocks formed in the early Paleozoic Caledonian, and only sporadically exposed in the northeast of Chengkou County.
Crustal changes mainly experienced 10 tectonic movements, among which Jinning movement, Indosinian movement, Yanshan movement and Himalayan movement were the strongest. Chongqing Ⅲ structural units mainly include Dabashan Depression Fold Belt, Southeast Chongqing Depression Fold Belt, Central Sichuan Platform Arch and Chongqing Depression Fold Belt, all of which belong to Yangtze paraplatform. Only a few areas north of Chengkou are the North Dabashan geosyncline fold belt of Qinling Fold Belt System. The fold direction in Chongqing is mostly northeast, followed by northwest and north-south, and less east-west. Most of the folds are comb-shaped folds of narrow anticline and wide syncline, followed by trough-shaped box-shaped folds of wide syncline and narrow syncline. There are only a few short axis backs, synclines or holes in the southwest of the city, and there are folds turning southwest near Chengkou County. The deep faults in Chongqing include Huayingshan deep fault, Qiyaoshan deep fault and Chengkou-Fangxian deep fault, which control the tectonic framework and landform. Due to the complex geological structure, many mountains, steep slopes and rivers cutting vertically and horizontally, Chongqing has serious geological disasters, with dangerous rock collapse and landslide being the most serious, followed by karst collapse and debris flow, ranking first among major cities in China.
2. Types of landforms
Chongqing is located in the hilly area in the southeast of Sichuan Basin, and there are many structural systems in the city, including the southeast Sichuan-Hubei-Hunan-Guizhou uplift belt, the west Sichuan-central fold belt, the middle Sichuan-east Chongqing fold belt, the south Sichuan-north Guizhou structural belt with syncline structure and the Dabashan arc fold fault zone in northeast Chongqing. Each structural system is composed of different rock strata, with very different structural characteristics and development rules, which shapes complex and diverse landforms. Generally speaking, it has the following four characteristics:
(1) The terrain is undulating and the layered landform is distinct. The terrain in the east, southeast and south is relatively high, and the highest point is Bashan Mountain and Eling Mountain, with an altitude of 2796.8 meters. Most of them are mountainous areas above 1500 meters. The lowest point is the Wushan Yangtze River, and the western part is low-lying, mostly hills with an altitude of 300 ~ 400 meters. The Yangtze River crosses the Wushan Mountains, forming Qutang Gorge, Wuxia Gorge and Xiling Gorge, namely the Three Gorges of the Yangtze River. Due to the different stages of landform development and the intermittent large-scale uplift of neotectonic movement, a 7-level layered landform of 300 meters to 2400 meters is formed in the area, which gradually decreases from north to south to the Yangtze River basin.
(2) There are various types of landforms, mainly mountainous areas. There are eight types of landforms in Chongqing, including Zhongshan, low mountain, high hill, Zhongshan, low mountain, gentle mountain, platform and flat dam.
(3) There are obvious regional differences in landform combination, mainly in hills. The western part of Huaying Mountain-Bayue Mountain is hilly, the parallel ridge and valley area between Huaying Mountain and Fangdou Mountain, the Daba Mountain area in the north, and the Wushan-Dalou Mountain area in the east, southeast and south.
(4) Karst landforms are widely distributed. In the eastern and southeastern regions, karst landforms are widely distributed, and underground and surface karst forms are well developed. The unique karst canyon landscape in eastern Sichuan is developed in the anticline belt mountain area. There are typical karst landscapes such as stone forest, peak forest, depression, residual hill, sinkhole, karst cave, underground river and canyon in the karst mountainous areas in the east and southeast.
Table 1- 1 Statistical Table of Main Geomorphological Areas in Chongqing (end of 2007)
Figure 1-2 Schematic Diagram of Topography Distribution in Chongqing
(2) parent material and soil type
Soil is a historical natural body, which is the product of the comprehensive action of climate, topography, parent material, biology, hydrology and human activities. Under the specific geological, geomorphological, climatic, hydrological and vegetation conditions, there are various soil types in Chongqing. According to the results of soil investigation, Chongqing * * * (Figure 1-) has 8 categories, 16 subcategories, 37 soil genera and1/4 soil species.
Figure 1-3 Schematic diagram of soil types distribution in Chongqing
Soil is mainly restricted by geological structure and stratum distribution. From the plane distribution of soil in Chongqing, purple soil develops in purple parent rock distribution area, limestone soil develops in limestone distribution area, and newly accumulated soil develops in newly alluvial parent rock. Triassic albite sandstone and Triassic, Silurian, Ordovician, Cambrian argillaceous limestone, yellow-green sandy shale and limestone developed into yellow soil. From the vertical distribution, the general trend is from low to high: newly accumulated soil-purple soil-yellow soil or limestone soil-yellow brown soil-mountain meadow soil.
1. Paddy soil
Paddy soil is widely distributed in valley terraces, hills, flat dams and erosion dams below the elevation of 1500m in Chongqing. Paddy soil in Chongqing is divided into three sub-categories, namely, flooded paddy soil, waterlogged paddy soil and latent paddy soil. Among them, flooded paddy soil with high fertility accounts for more than 80% of paddy soil; Secondly, water-holding paddy soil accounts for about 10% of paddy soil. Latent paddy soil is a typical low-yield paddy soil, accounting for only 5.8% of paddy soil. This kind of soil is mainly distributed in deep valleys and low-lying dams with poor irrigation and drainage conditions, which are mainly cold, soaked and toxic. Paddy soil has moderate pH value, good soil structure and relatively harmonious water, heat, gas and fertilizer. If there is water source guarantee and supporting irrigation and drainage facilities, high and stable yield farmland can be built.
2. Purple soil
Purple soil is the most widely distributed soil in Chongqing, and it is also the main soil for dry farming. Widely distributed in hills, low mountains and flat dams between 500 and 800 meters above sea level in Chongqing. Geographically, the hilly areas in the west, Fuling, Nanchuan and Fengdu in the middle and Yunyang, Zhongxian, Wanxian and Kaixian in the east are distributed in blocks in the middle and low mountains, most of which are within 800 meters above sea level. Purple sand and mudstone are widely distributed, so purple soil is particularly concentrated.
3. Loess
Yellow soil is mainly distributed in the middle and low mountains and hills at an altitude of 500 ~ 1500m and the second, third, fourth and fifth terraces along the Yangtze River and its tributaries. About 1/4 is cultivated land, which is an important dry grain and cash crop soil in Chongqing, and most of the rest is woodland, which is also one of the typical phosphorus-deficient soils.
4. Lime soil
Limestone soil is mainly distributed in the low anticline exposed by limestone strata below 1500 meters above sea level and in the valley area of Zhongshan, with a small amount distributed in Zhongshan. In terms of regional distribution, it is mainly distributed in Fuling, Wanzhou, Qianjiang and other areas in central and southeastern Chongqing.
5. Newly accumulated soil
Neoaccumulation soil is the main agricultural dry land soil along the rivers in Chongqing, which is developed in Quaternary strata. Mainly distributed in the Yangtze River, Jialing River, Wujiang River, Fujiang River, Daning River and other low-grade land along the Yangtze River, and most of them have been reclaimed as cultivated land, which is agricultural land with high fertility level.
6. Yellow brown soil
Yellow brown soil belongs to the soil type of vertical zone in mountainous soil. It is generated and developed under warm, cool and humid biological climate conditions, so the soil-forming process is high, which is different from yellow soil and brown soil, and has the development characteristics of yellow soil and brown soil at the same time. It is mainly distributed in Zhongshan, Chengkou, Wushan, Kaixian, Fengjie and Wuxi, with an altitude of1.500m.. Mostly woodland and grassland.
7. Red soil
Red loam is a typical low-yield soil type, with deep soil layer, thin plough layer, heavy texture, poor permeability, low effective nutrient content, weak fertilizer supply capacity, difficult farming, narrow suitability and low yield. It is mainly distributed in the dam area in the middle of Xiushan County, the Meijiang River Valley in the south, the Hong 'an-Yajiang River Valley and the western valley.
8. Mountain meadow soil
Mountain meadow soil is mainly distributed in the peak-cluster depression of Daba Mountain Plateau in the east of Chongqing at an altitude of1800 ~ 2,700 meters, and the gentle and low-lying areas in the middle and upper karst mountains at an altitude of 1400 meters in Fuling, Fengdu, Wulong, Pengshui and Youyang. The soil is acidic or slightly acidic, the texture is heavy to light sticky, and the content of nutrients such as organic matter and phosphorus is high. Therefore, the forage grass is rich, the coverage rate is above 80% ~ 90%, and the plants are as high as 30 ~ 40 cm, which is a good field for animal husbandry.
(3) Climate
Chongqing's climate is in the transitional zone between south temperate zone and subtropical zone, and belongs to subtropical humid monsoon climate. Agricultural climatic resources are abundant, and agricultural climatic conditions are superior, especially the agricultural three-dimensional climate, which has the characteristics of hot summer and warm winter, light and heat in the same season, long frost-free period, abundant rainfall and humid and cloudy. The annual average temperature is 19.0℃, and the annual total rainfall is 1439.2 mm, which is suitable for agriculture in all seasons and conducive to the comprehensive development of agriculture, forestry and animal husbandry.
(1) It is warm in winter and full of heat in early spring. There is little difference in temperature between north and south latitudes in Chongqing, but the vertical difference is obvious because of the great difference in terrain height. The distribution of annual average temperature in China is as follows: flat dam hill in the valley 17.5℃ ~ 19.0℃, area at an altitude of 400 ~ 600 meters 16.5℃ ~ 17.5℃, area at an altitude of 600 ~ 800 meters14. 800 ~ 1000m altitude 14.0℃ ~ 15.0℃, Zhongshan 1000m altitude 14℃ altitude (Figure 1-4). The active accumulated temperature in Chongqing decreases with the elevation. Annual average accumulated active temperature > 0℃ is 6000℃ ~ 6900℃ in Pingba hilly area and below 6000℃ in mountainous area; The annual average active accumulated temperature in Pingba hilly area is ≥ 10℃ between 5100℃ and 6200℃, and less than 5100℃ in mountainous area; The annual average active accumulated temperature ≥ 15℃ in Pingba hilly area is between 4500℃ and 5300℃, and below 4500℃ in mountainous area. Stable through the active accumulated temperature 10℃ ~ 20℃, the flat dam hilly area is between 3700℃ ~ 5000℃, and the mountain area is less than 3700℃.
Figure 1-4 Schematic diagram of annual average temperature distribution in Chongqing.
(2) Sufficient precipitation and high air humidity. Chongqing is located in the middle and upper reaches of the Yangtze River with abundant precipitation, with an annual precipitation of 986 ~1439 mm. There is a lot of night rain, and the total amount of night rain accounts for 60% ~ 70% of the total annual precipitation. Night rain and sunny days are beneficial to plant photosynthesis, but the air is humid and the annual average relative humidity is as high as 80% (Figure 1-5).
Chongqing has weak solar radiation and short sunshine time. Solar radiation and sunshine hours are the least in China, with annual solar radiation of only about 3390 MJ/m2 and sunshine hours of 856.2 hours (Figure 1-6). Because of weak solar radiation, less light, humid air and small temperature difference between day and night, it is not conducive to the growth of dry matter of crops and the accumulation and coloring of sugar in fruits, but more beneficial to the growth and development of stem and leaf plants.
(4) Light, heat and rain should be matched in the same season. The seasonal distribution of light energy, heat energy and rainfall varies greatly, but they match each other in the same season. The resources are concentrated in the warm season, accounting for about 65% of the total in the whole year from May to September. Agricultural climate resources in warm season are obviously superior to those in cold season.
(5) The vertical distribution of agro-climatic resources is quite different. In a certain range, precipitation increases with height, temperature decreases with height, annual sunshine hours decrease with height, summer drought decreases with height, and cold (freezing) damage increases with height. Therefore, agriculture is a three-dimensional layout and all-round development.
(6) Agrometeorological disasters are frequent. There are mainly summer drought, low temperature in spring and autumn, rainstorm and flood, gale and hail. Hail mainly occurs in mountainous areas in late spring, early summer and midsummer, and gale and hail often appear together (Figure 1-7). Cold waves occur three times a year, and strong cold waves occur 1.5 times a year. Summer drought occurs once every 3 to 5 years, and the western and northern regions are more important. The summer drought in 10 occurs about 6-8 times, usually accompanied by continuous sunny, hot and high temperature weather, especially in the central region (Figure 1-8).
Figure 1-5 Schematic diagram of annual precipitation distribution in Chongqing
Figure 1-6 Schematic diagram of annual sunshine hours distribution in Chongqing
Figure 1-7 Schematic diagram of hail disaster distribution in Chongqing
Figure 1-8 Chongqing Drought Index Analysis and Distribution Diagram
(4) Hydrology
Chongqing has many rivers, dense water networks, huge hydropower reserves and great development potential. The average annual total amount of water resources is about 500 billion cubic meters, and the water area per square kilometer ranks first in the country. The theoretical reserve of hydropower resources is 654.38+04382800 kilowatts, and the exploitable capacity is 7.5 million kilowatts. The total installed capacity of exploitable hydropower per square kilometer in the city is three times of the national average, and the development of hydropower resources is leading the country.
1. Surface water
Chongqing runoff is completely replenished by atmospheric precipitation, and its interannual variation and intra-annual distribution are positively correlated with precipitation in the same period. At the same time, affected by the terrain, there are great differences between regions. According to the statistics of Chongqing for many years, the annual rainfall in most areas is between 1000 ~ 1200mm, with an average annual rainfall of 99.57 billion cubic meters. There are many rivers and water networks in this city. Except the Yangtze River and its main tributaries, Jialing River and Wujiang River, there are 10 rivers with a basin area of over 3,000 square kilometers, and 436 rivers with a basin area of over 30-50 square kilometers. The main rivers are Yangtze River, Jialing River, Wujiang River, Fujiang River, Qujiang River, Qijiang River, Yulin River, Longxi River, Laixi River, Furong River, Anzhu River, Daning River, Xiaojiang River and Renhe River. Among them, except Renhe River which pours into Hanshui River, the rest belong to the Yangtze River system. The main stream of the Yangtze River crosses the whole city from west to east, forming a water system of five tributaries and several small and medium-sized rivers in the north-south direction (Figure 1-9).
Figure 1-9 Schematic diagram of water system distribution in Chongqing
2. Groundwater
Groundwater in Chongqing is replenished by atmospheric precipitation and controlled by geological structure, topography and spatial distribution of water content. Due to the complex geological structure and hydrogeological environment in China. There are three types of groundwater in Chongqing: carbonate fissure karst water, clastic pore fissure water and bedrock fissure water. According to statistical analysis, the annual total amount of groundwater in Chongqing is 65.438+0.49 billion cubic meters, of which 78% is carbonate fissure cave water, 65.438+06% is clastic pore fissure water and 6% is bedrock fissure water.