Because of the global warming and other related reasons, the intensity of ultraviolet (UV) radiation is increasing annually in Lhasa. The UV index reaches 70 w/㎡this year, while only 47 w/㎡last June. According to the scientific research, when the UV index is beyond the 30 w/㎡, it is easy to get sunburned after sun exposure for about 20 minutes.

Lhasa enjoys good air quality, which has low suspensions and small filtrations compared with other provinces of China, thus there is only slight damage on the ultraviolet when it radiates to the land, which makes the UV index much higher. In the afternoon, the higher UV index is, the stronger anti-radiation the land produces. The land absorbs the sun’s heat in the morning, while releasing it in the afternoon. Moreover, with the direct radiation from the sun, the UV radiation is much stronger. However, big temperature difference between day and night, as well as the low humidity in Lhasa make the ground’s anti-radiation effect small.  

Li Wenhua, a senior engineer in Lhasa meteorological bureau, reminded that UV index in Lhasa might be the highest among all the provincial capitals in China. The UV level here reaches the peak from 2pm to 6pm. In the course of a whole year, Lhasa has the strongest UV radiation in summer.