Abstract: By using the data of total cloud amount at 22 stations over Tibet in 1971-2008, the change trends of total cloud amount were analyzed. The results show that the annual average total cloud amount decreased remarkably in most parts of Tibet, especially in the mid-west of Naqu where the trend was -2.32%/10a; but over the southern edge of the Tibetan Plateau, the reducing trend was not significant. Correlation analysis demonstrates that total cloud amount was correlated positively with precipitation and relative humidity, and negatively with sunshine duration, average temperature and diurnal range of temperature. The Hurst index of total cloud amount shows that the total cloud amount had a decreasing trend in most parts of Tibet; this trend will continue, and will not change in a short period of time.

Key words: Tibet, total cloud amount, rescaled range analysis (R/S analysis)