The decreasing wind speed in southwestern China during 1969–2009, and possible causes

Abstract Daily wind speed data from 110 stations in southwestern China were analyzed to determine trends, spatial differences and possible causes. There was a statistically significant decrease of 0.24 m/s per decade in the annual mean wind speed during the period 1969–2009. The decreasing trend was faster (0.37 m/s/10a) during 1969–2000. Between 2001 and 2009, there was a significant increase. The pattern of seasonal changes was similar. Stations with stronger, significant decreasing trends were mainly on the Xizang Plateau, the Hengduan Mountains and the Yunnan Plateau, and stations with significant increasing trends were mainly in the Sichuan basin, indicating the influence of altitude on wind speed. Surface wind speeds in southwestern China have been affected in recent years by both the changed large-scale atmospheric circulation and regional and global warming, while the weakening surface pressure gradient between high and low latitudinal regions may be an important contributor to the decreased wind speed under the asymmetric warming during 1969–2009. The data indicated a positive correlation between wind speed and sunshine duration suggesting another possible influencing factor. Topographical influences are evident in the higher annual and seasonal trends at summit and intermontane basin stations and the lower trends at valley stations.