Rainy season change in Sanjiangyuan, China area based on the meteorological stations data

The Sanjiangyuan area is famous as the Chinese water tower, it is a transition zone of semi-humid, semi-arid and arid area. An area of about 400,000 square kilometers and the water source of billions of people, also the ecological barrier of the whole of Asia's economic and social development.Based on the daily rainfall data of 13 meteorological stations in Sanjiangyuan area from 1985 to 2015, the rainfall indexes such as the rainy season from the beginning and the ending of the rainy season were extracted. And the trend of rainy season in the study area was analyzed. The results show that the daily rainfall in the Sanjiangyuan area accounts for more than 50% of the annual rainfall; the onset of the rainy season in the eastern part of Sanjiangyuan has a delayed trend and the central area has a tendency to advance; the number of days in the rainy season has decreased in the past 30 years, reduced 4d. There is a positive correlation between the starting date of rainy season and the average rainfall in the rainy season. The changes of these rainy seasons are of great significance to the economic development and ecological protection of the region.