What are the hydrological characteristics of rivers in Gansu Province?

1) From the geographical distribution of precipitation, Longnan, Gannan, Qilian Mountains and other rocky mountain forest areas are semi-humid areas, with normal annual precipitation above 600mm; most of the Yellow River Basin east of Lanzhou is semi-arid In this area, the annual precipitation is generally around 400mm. The precipitation to the west of Lanzhou and the Hexi Corridor is below 100-300mm, which is an arid area and an extremely arid area. Although the climate in Hexi is extremely arid, agricultural production is relatively stable due to the Qilian Mountain glaciers and reservoir regulation and a developed irrigation system, and it is known as the granary of Gansu. Most of the central and Hedong areas are rain-fed agricultural areas. If the limited precipitation is evenly distributed in important seasons of agricultural production, although the amount of water is insufficient, it can solve basic agricultural production problems; under conditions of scarce precipitation and long-term drought, the interannual variation of precipitation is very large, and the spatiotemporal distribution is extremely Uneven, resulting in the coexistence of local drought and flood disasters in short periods of time. Although the Longnan region receives more rainfall, it is also prone to drought due to the steep mountain slopes, deep ravines, thin soil layers, and severe soil erosion. (2) Evaporation Another main feature of the dry climate in Gansu Province is the large evaporation capacity of the water surface, and the evaporation is greater in places with less precipitation. The evaporation capacity of the water surface is generally greater than that in eastern areas at the same latitude. This is also the reason for the drought and water shortage in Gansu Province. An important reason. However, in Zhangye, located in the middle of the Hexi Corridor, due to the confrontation between the Qilian Mountains and the northern mountains of the corridor, its water surface evaporation capacity is smaller than that of the arid desert grassland area of ??Inner Mongolia in the east at the same latitude; the evaporation capacity of the water surface in the west of Jiuquan is smaller than that of Xinjiang in the west and Inner Mongolia in the east at the same latitude. feature. The overall spatial change trend of water surface evaporation capacity is opposite to that of precipitation, gradually increasing from southeast to northwest, while also decreasing with increasing altitude. The annual water surface evaporation capacity near Minshan Mountain in the southeast is less than 700mm, and the annual water surface evaporation capacity north of Dunhuang-Anxi is more than 2000mm. The places where the annual water surface evaporation capacity is less than 700mm are: Minshan, Dieshan, Taizishan and other few peaks, as well as Gannan Dayu Forest Farm and Taohe Yeliguan Forestry; the areas where the annual water surface evaporation capacity is greater than 2000mm are Jingtai-Minqin Zhongquanzi- The arid desert area east of the Anxi-Dunhuang line. The annual evaporation in the Longnan and Gannan Plateau is less than 400mm; the annual evaporation in the Longzhong and Longdong areas east of Lanzhou is between 400-500mm; in the Hexi region, except for the Qilian Mountains, the annual evaporation is basically equal to the actual precipitation, and the annual evaporation in the Qilian Mountains is less than 300mm. (3) Runoff, except for southern Longnan, generally has less precipitation and a smaller runoff coefficient. The topographic uplift of the tall and uplifted mountains within the territory increases precipitation, so mountains such as Taizi Mountain, Liupan Mountain, and Qilian Mountain have become the source of runoff in our province. Main formation area. At the same time, the above-mentioned mountainous areas are also high-value centers of runoff in our province. A few mountain peaks such as Minshan, Dieshan, Taizishan, and Lenglongling have an annual runoff depth of 500-600mm; the Qilian Mountains, Liupan Mountains, Gannan Plateau, and Longnan Mountains have The runoff depth is 100-300mm; the Hexi Corridor and the Beishan Desert Gobi are vast flowless areas and are runoff consumption areas; the rest of the area transitions from southeast to northwest to the Qilian Mountain Piedmont area, and the annual runoff depth is reduced from 50mm to 5mm. According to the evaluation results of "Surface Water Resources of Gansu Province", the runoff in mountainous runoff forming areas accounts for 95% of the province's self-generated runoff, and the runoff in runoff-poor areas accounts for 5% of the province's self-generated runoff. (4) Heavy rain. Heavy rain and flood disasters in Gansu are mainly short-duration local heavy rain floods, and hail disasters are also mainly short-duration and small-scale. The occurrence of local heavy rain, floods and hail disasters is highly random and sudden, and the causes are extremely complex. Climate change in our province is controlled by high-altitude westerly airflow and the Tibetan Plateau monsoon for most of the year. High- and low-pressure systems mostly evolve against the background of the above-mentioned large-scale weather systems, forming large-scale weather systems. In addition to the water vapor transported by the southeast monsoon and southwest monsoon, water vapor formed by local precipitation is also an important source. When the western Pacific subtropical high extends westward, pressure gradients are formed in the southeast and southwest directions, providing dynamic conditions for the transport of water vapor from the Pacific and Indian Oceans to the northwest inland. The warm and humid airflow from the southeast and southwest travels long distances and is blocked by high mountains. A considerable part of the moisture will fall in the areas passing along the way; the rest of the water vapor is stored in large inland basins, such as the Guanzhong Basin and Sichuan Basin, and then It is further transported to the northwest inland, and many valleys and small basins in the mountains in our province also become water vapor reservoirs. Once it encounters southeasterly winds or cold air from the northwest, a large precipitation process will occur. Heavy rainstorms and extremely heavy rainstorms are most likely to occur in the Jialing River and Jinghe river basins across the province. The southern part of Longnan is on the edge of my country's famous heavy rain areas - the Qinba Heavy Rain Area and the Western Sichuan Heavy Rain Area. Therefore, heavy rainstorms occur more frequently, are large in magnitude, wide in area, and cause severe disasters. Secondly, Liupan Mountain, Majian Mountain, Taizi Mountain, Huajialing, Qilian Mountain, etc. are all famous heavy rain centers in Gansu. (5) Floods Gansu is affected by the continental monsoon climate. More than 90% of floods occur from June to September, and the annual maximum floods in most rivers occur from July to August. The timing of flooding in each river coincides with heavy rains. Spring floods occur early and frequently in various rivers in Hexi, with peaks occurring almost every day, which has a great impact on Hexi's industrial and agricultural production. Larger rivers such as the main stream of the Yellow River, Jialing River, Tao River, and Heihe River have large flood magnitudes and long duration. Floods in other rivers generally surge and fall, causing great harm to water conservancy projects.

(6) Dry water. Under natural conditions, the dry season for most rivers in the province occurs from November at the end of the year to April of the following year, and the lowest flow mostly occurs from January to February. Due to the influence of human activities and the underlying surface and altitude of the river basin, the times when the lowest flow occurs in each river are not consistent. Even different reaches of a river have different times when the lowest flow occurs. In some rivers, the lowest flow occurs in the upper and lower reaches. The busiest time is half a year apart. Generally speaking, rivers east of Wushaoling and rivers west of Wushaoling exit above the mountain pass. The dry season and the lowest flow time are also from January to February. However, the river sections below the mountain pass and in the desert plain area have The dry season and the lowest flow time are from July to August. (7) Sediment Due to the poor ecological environment, the coverage rate of forests and other vegetation is very low. The loess area and the Longnan Mountains are serious water and soil erosion areas and debris flow-prone areas. Most rivers have high sand content; desertification, sandstorms and sandstorms in Hexi The activity is very frequent. The ecological environment and soil erosion have generally deteriorated and partially improved. According to statistics in 1999, the province's multi-year average total sediment transport volume was 546.91 million tons. Among them, the multi-year average sediment transport in the inland river basin is 12.75 million tons; the multi-year average sediment transport in the Yellow River Basin is 492.01 million tons; and the multi-year average sediment transport in the Yangtze River Basin is 42.15 million tons. The results of the "Gansu Province Surface Water Resources Assessment" in 1979: the multi-year average sediment transport in the province is 579 million tons, of which the multi-year average sediment transport in the inland river basin is 11.1 million tons; the multi-year average sediment transport in the Yellow River Basin is 518 million tons. tons; the multi-year average sediment load in the Yangtze River Basin is 49.9 million tons. Comparing the 1999 assessment data with the 1979 assessment data, the province's multi-year average sediment transport volume decreased by 32.09 million tons; the changes in each river basin were inconsistent. The multi-year average sediment transport volume in the inland river basin increased by 1.65 million tons; the multi-year average sediment transport volume in the Yellow River Basin increased by 1.65 million tons. The sediment transport volume decreased by 25.99 million tons; the multi-year average sediment transport volume in the Yangtze River Basin decreased by 7.75 million tons. The main reason for the increase in the multi-year average sediment transport in the inland river basin is that disordered gold mining and licorice digging in the basin have led to vegetation destruction and soil erosion; the main reason for the decrease in the multi-year average sediment transport in the Yellow River Basin is that the multi-year average sediment transport in the Yellow River Basin has continued to The reduction in drought and precipitation has reduced the amount of soil erosion caused by floods, and soil and water conservation measures have also played a certain role. The Yangtze River Basin has implemented three phases of water and soil erosion control projects in the upper reaches of the Yangtze River, which have shown certain soil and water conservation effects and reduced the average annual sediment load in the basin. The rivers with an annual sediment transport volume of more than 100 million tons include the mainstream of the Yellow River, Wei River, and Malian River; the rivers with an annual sediment load of 100 million to 50 million tons include the Zuli River, Hulu River, and Jinghe River. (8) Water quality 1. Water quality type: Rivers in the province are dominated by bicarbonates. This type of water has the widest distribution range, including the Qilian Mountains and piedmont alluvial fan areas in Hexi, and the Linxia-Longxi-Gangu-Zhuanglang line. Southeast, all belong to this natural water chemistry type. In the Qilian Mountains and piedmont alluvial fan zone in Hexi, and in the southeast of the Linxia-Longxi-Gangu-Zhuanglang line, the salinity of water is between 100-300 mg/L; the lower reaches of the three major river systems in Hexi, the Zuli River and Qingyang The salinity of river water and groundwater in Huan County is between 500-1000mg/L, and in some places the salinity exceeds 1000-2000mg/L. 2. Water pollution status: According to the survey and evaluation of the "1999 Gansu Provincial Water Resources Bulletin", the total wastewater discharge in the province reached 947 million tons, of which 408 million tons were discharged up to standard, accounting for 43.1% of the total wastewater discharge; The average daily discharge is 2.594 million tons, of which the average daily discharge of industrial wastewater is 2.1222 million tons, accounting for 81.8%, and the average daily discharge of domestic sewage is 471,800 tons, accounting for 18.2%. The water quality monitoring and evaluation of the 7108km of major rivers in the province was carried out. The length of Class I water rivers was 2481km, accounting for 34.9%; the length of Class II water rivers was 1500km, accounting for 21.1%; the length of Class III water rivers was 1597km, accounting for 22.5%; the length of Class IV water rivers was 1597km, accounting for 22.5%; The length of rivers is 706 km, accounting for 9.9%; the length of rivers with Class V water is 368 km, accounting for 5.2%; the length of rivers with Class V water above is 456 km, accounting for 6.4%. (9) Water resources: The province’s average self-produced water resources for many years is 28.6207 billion cubic meters. Among them, the multi-year average water resource volume in the inland river basin is 5.5641 billion cubic meters; the multi-year average water resource volume in the Yellow River Basin is 12.9193 billion cubic meters; and the multi-year average water resource volume in the Yangtze River Basin is 10.1473 billion cubic meters. The amount of non-duplicated groundwater resources is 837.2 million cubic meters. Among them, the non-duplicated groundwater resources in the inland river basin are 513.8 million cubic meters; the non-duplicated groundwater resources in the Yellow River Basin are 357.4 million cubic meters; the non-duplicated groundwater resources in the Yangtze River Basin are 02.0 million cubic meters. (10) Hydrological Zoning According to the research results of "Gansu Province Surface Water Resources Assessment", the whole province can be divided into 7 hydrological regions: 1. Subtropical humid zone in the valley of southern Longnan; 2. Warm temperate humid zone in northern Longnan; 3. Central Longnan The southern semi-humid area; 4. The semi-arid area in central and northern Longxi; 5. The semi-arid area in the southern Qilian Mountains; 6. The alpine and humid area in southern Gansu; 7. The arid area in the Hexi Corridor. (11) Flood and Drought Disasters Gansu is a province suffering from serious droughts. Drought disasters are not only frequent but also large-scale and long-lasting. They rank first among various natural disasters, accounting for 50.1% of the area of ??various natural disasters.

Judging from the annual change distribution of disasters, drought has inter-annual persistence. Droughts generally last two to seven years. And it is increasing year by year. Heavy rain, flood and hail disasters are also very serious, second only to drought, accounting for 22.1% of losses from various natural disasters. Flood disasters are mainly local heavy rain floods. Serious local heavy rain and flood disasters are often accompanied by hail and mudslides, and the main disasters are floods; hail disasters usually also cause floods, and the main disasters are hail disasters. Local heavy rains cover a small area, are short-duration and high-intensity. They often move quickly and sweep across a line. They occur frequently and are extremely destructive, forming extremely heavy rain floods in small watersheds. Its intensity often reaches its limit, and sometimes exceeds the theoretical value of the maximum local heavy rain, making the disaster extreme and the chance of recurrence extremely rare. Spectrum analysis of 500 years of historical data on floods and droughts in Gansu shows that the most common cycles of floods, droughts and hail disasters are: a 3-year cycle, a quasi-5-year cycle that is a 4-6 year cycle, and an 11-year cycle. 56 year cycle. Among them, the quasi-5-year cycle and the 11-year cycle are the most active. The former corresponds to the quasi-5-year cycle of El Ni?o, which fully demonstrates that El Ni?o has a profound impact on floods, droughts and hail disasters. The 11-year cycle corresponds exactly to the 11-year sunspot activity cycle.