6. Spatial and Temporal Variation of Wind Speed in Southwestern China

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 0.24m/s/10a in the annual mean wind speed during the period 1969–2008. The decreasing trend was faster (0.37m/s/10a) during 1969–2000. Between 2001 and 2008, 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 the regional and global warming. The analysis have confirmed that the decreasing wind speed during 1969–2000 was caused mainly by the decreasing monsoonal circulation and Westerlies, and the strengthening latitudinal wind speed has made some contributions on the increasing wind speed after 2000. And what’s more, the strengthening Xizang monsoon has also made some contributions to wind change, and it indicated lower wind speeds related to increased temperatures, particularly to a rise of the minimum temperature in recent years. The weak wind speed may also be caused by the asymmetric decreasing latitudinal gradients of surface temperature and pressure gradient during 1969–2008. The data indicated a positive correlation between wind speed and sunshine hours 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. In addition, a minor influence from urban effect on wind speed also has been founded.