Meteorological and Hydrological Data of Bashan Reservoir

The basin where Bashan Reservoir is located belongs to the East Asian monsoon region and has a continental climate. The four seasons are distinct and the temperature difference varies greatly. Southeast and southwest winds prevail in summer, and the weather is hot. The highest temperature in the dam area is 40℃, with frequent cold and warm air activities and abundant water vapor. Rainstorms and floods often occur during this period. In winter, northeast wind and northwest wind prevail, water vapor sources are scarce, precipitation is scarce, the weather is cold and dry, and the lowest temperature in the dam area is -20℃. The maximum wind speed in the dam area is 20m/s, and the average maximum wind speed in July, August and September is10m/s. The annual average rainfall is 738mm, which varies greatly from year to year. The maximum annual rainfall is 1522 mm (1964) and the minimum annual rainfall is 432 mm (198 1 year). Rainfall is unevenly distributed in a year, mostly concentrated in the flood season (June to September). It accounts for about 69% of the annual precipitation. In the flood season (June-September), the average annual precipitation is 545 mm, the average annual runoff is 408 million cubic meters, and the average annual runoff in the flood season is 310.20 billion cubic meters. The annual average water surface evaporation is 12 17mm, and the annual average land evaporation is 500mm.

The main meteorological causes of rainstorm in reservoir basin are frontal, typhoon, cyclone, shear line and vortex. Yi River is a seasonal mountain stream rain and flood channel. Every flood season, the rainfall is concentrated and the flood rises and falls sharply. The flood process lasts for a short time, and the peak is high and thin.

According to the historical flood data, there is flood in 163 1 year, with the river flooding and few drifters. 1649 overflow in autumn and July; 1685, flood, rain in Lin Xia, the two rivers decided to sail on the flat ground, which is the hunger of the people in winter and spring; Yi River overflowed in June1702; The flood in 1730 and the rainstorm in June 19 flooded the Lushe in Tianhe; 177 1 May, rainy, Yi Shu flooded, and Zhaobei Lake in the northeast was trapped in Shushu.

In addition, the flood years are: 1536, 1553, 1593, 1646, 1647, 1680,17655.