Traditional Culture Encyclopedia - Weather forecast - Climatic and hydrological conditions

Climatic and hydrological conditions

The project area is bounded by Bayan Kara, and the northeast is divided into plateau sub-frigid zone-semi-arid climate zone controlled by the dry and cold airflow of the west wind in Central Asia, and the southwest is divided into sub-frigid zone-cold temperate climate zone affected by the southwest monsoon. The main climatic characteristics are as follows:

1) The solar radiation is strong, with the annual total radiation of 7000×106 ~ 5500×106j/m2, and the sunshine time is long, with the annual sunshine time exceeding 2000 h. ..

2) The winter is cold, the low temperature lasts for a long time, the summer is cool, and the surface temperature is consistent with the temperature change. The annual average temperature is -4.2 ~ 5.6℃, and the extreme minimum temperature is -45℃. 65438+ 10, the monthly average temperature is -0.5 ~- 17℃, the July average temperature is 5 ~ 14℃, and the daily average temperature in most areas is below 0℃ for more than 4 months. The temperature difference between day and night is large, but the annual temperature difference is small. 10 The surface temperature is-15 ~-3.5℃ in October, and 10.5 ~ 18℃ in July. From June 165438+ 10 to March of the following year, the surface soil temperature at an altitude of 4200m was below 0℃ in the depth range of 5 ~ 40 cm.

3) The humidity is low, and the evaporation is large, with the annual evaporation reaching1200 ~1700 mm. ..

4) The wet and dry seasons are distinct, there are many rainy days, the rainfall intensity is small, there are many days of snowfall, and the snowfall is large. The annual precipitation increased from 265.6 mm at Wudaoliang Station in the northwest to more than 700 mm in Rangtang and eastern Aba. The annual precipitation is concentrated in May ~ 10, accounting for about 80% of the annual precipitation. More than 0. 1mm precipitation days are around 150d, and rainstorm days are rare. In areas above 3500 meters above sea level, 20% ~ 30% of annual precipitation comes from snowfall.

5) Low air pressure and thin oxygen. The annual average air pressure is 577 ~690hPa, and the annual average oxygen content is 0. 174 ~ 0.204 kg/m3.

6) High wind speed and low wind pressure. The maximum wind speed exceeds 18m/s, and the wind pressure is only 67% of the sea level at an altitude of 4000m.

7) Severe weather such as gale, frost, snowstorm, hail and thunderstorm.

The water system characteristics of each basin in the project area are described as follows:

1) Daqu River Basin: mainly located in Ganzi County and sertar county. Daqu River in Ganzi County is 154km long, 32m wide and 1.5m deep, and it gathers many tributaries such as Zach and blossoming. The maximum discharge is 2 1.5m 3/s, the minimum discharge is 5.8m3/s, and the annual average runoff is 1.52 million m3. Sertar county Daqu River is 38km long, with a drainage area of 84 1km2, a drop of 120m, an average gradient of 3.2%, an average runoff depth of 270mm, an average annual runoff of 7.2m3/s and an average annual runoff of 227m3.

2) Niqu River Basin: mainly located in Ganzi County and sertar county. The Niqu River in Ganzi County is 42km long, 30m wide and 1 m deep, with a maximum flow of 390m3/s and a minimum flow of 8. 1 m3/s, with an average annual runoff of 2.05 billion m3. The Niqu River in sertar county is 92km long with a drainage area of 3882km2, with an average river gradient of 3.3%, an average runoff depth of 280mm, an average annual runoff of 2.88m3/s and an average annual runoff of 965.438+0.4 billion m3.

3) Sequ River Basin: The total length in sertar county is 144km, with a basin area of 3234km2 and a drop of 1 1,000m, with an average gradient of 6.92%. The average runoff depth is 326mm, the flood and dry water level is 8 ~ 10 m, the annual average runoff is 33.32m3/s, and the annual average runoff is10.50 billion m3. Precipitation is the main supply of rivers, followed by ice and snow.

4) Duke River Basin: the discharge of Rangtang County is 180km, the basin area is 4400. 15km2, the drop is 950m, the average gradient is 5%, the maximum gradient is 13.9%, the maximum discharge is 185 m3/s, and the minimum dry.

5) Malqu River Basin: The river length in banma county is 1 14.8km, the basin area is 303 1.29km2, the entrance elevation is 3680m, the exit elevation is 3246m, and the riverbed gradient is 1.87%, including large and small rivers/kloc-along the way.

6) Ake River Basin: mainly in banma county, with a small amount in Aba County. The length of the river in banma county is 14.9km, the drainage area is 822.4km2, the average riverbed gradient is 2.49%, the annual average flow is 6.6m3/s, and the annual average runoff is 206.6m3 ..

Surface runoff in the project area mainly comes from precipitation, supplemented by seasonal snow melting and ice melting. 165438+ 10 to March of the following year is the dry season, and the runoff is replenished by groundwater; April-May is the transition period of low water and abundant water, and runoff is supplemented by snow melting and spring rain. June ~ 10 is the wet season, which is the main formation period of runoff. The annual runoff changes greatly. The ratio of maximum and minimum annual runoff of Ganzi Station and Daofu Station in Yalong River diversion area is 2. 14 and 2.27 respectively, and the coefficient of variation Cv is 0. 19 and 0.22 respectively. The ratios of the maximum and minimum annual runoff of Zubenzu Station and Chusijia Station in Dadu River diversion area are 1.88 and 2. 16 respectively, and the Cv values are 0. 17 and 0.2 1 respectively. The sediment yield in the project area is small, the average sediment concentration is less than 1kg/m3, the average erosion modulus for many years is around 100t/km2, and the average sediment discharge for many years is less than 100t ... The sediment discharge is concentrated in the flood season, accounting for 95% of the annual sediment discharge. See table 1-4 for the annual average runoff and adjustable water volume of some proposed diversion dam sites.

Table 1-4 Average annual runoff and adjustable water volume of the proposed diversion dam site: 100m3.

There are few rainstorms in the project area, and the floods are mainly formed by the continuous regional rainfall process with daily rainfall greater than 5 mm According to statistics, a moderate to heavy rain usually lasts for 3 ~ 5 days, with a total rainfall of 30 ~ 50 mm The duration of two consecutive rainfalls is generally 1 ~ 15d, and the duration of three rainfalls can be as long as 20 days. A rainfall process has a wide range, which can be distributed in three water diversion engineering areas: Tongtianhe, Yalong and Dadu.

There are two causes of floods in the project area: one is the non-flood season snowmelt flood that occurred in April-May; The second is the flood season from June to 10. The flood time in the project area is concentrated, and the annual maximum flood peak appears from May to 10, of which 50% occurs in July, followed by August and September. 70% of the floods appear in the form of compound peaks, with an average duration of 30 days, and the elderly reach 50 days. The average unimodal flood process is about 15d. The flood is short and fat, and the maximum instantaneous discharge is not much different from the maximum discharge of1d. The fatness coefficient of the maximum discharge of 1 ~ 15d is 0.95 ~ 0.70. The flood peak is low and the flood volume is large. The annual average maximum flood peak discharge of Zhimenda, Ganzi, Zumuzu and Chusijia stations is 2060m3/s, 1 187m3/s, 1267m3/s, 9 13m3/s respectively, and the measured annual maximum value is 30 days. The ratio of the maximum value to the minimum value of the flood characteristic values of the above stations is within 5.0, and the Cv value is less than 0.38 1, indicating that the annual variation of the flood in the project area is relatively stable and the flood amplitude is small. The flood peak modulus of water diversion project areas in each basin increases from upstream to downstream, with the largest in Dadu River and the smallest in Tongtian River. The regional flood peak area index is Dadu River 1.05, Yalong River 1.29 and Tongtianhe River 2. 12.