Climatology and trends of wet spells in China

Climatological features and variations of wet spells, especially their trends over China, are investigated using a dataset of 594 meteorological stations across China from 1951 to 2003. The results show that the lower the latitude is, the longer the annual duration of wet spells is. The mean annual precipitation from wet spells is higher in southeastern coastal areas and much lower in western and northern China. The longest wet spells are found in Southwest China and the eastern Tibetan Plateau. The maximum daily precipitation of wet spells decreases from the southeast to the northwest, with the highest in southeastern coastal areas and the lowest in western China. The trends of wet spells exhibit striking regional differences. In most areas of western China, the annual number of days in wet spells has slightly increased, but significantly decreased over North China, Central China and Southwest China. The annual precipitation amount from wet spells displays significant downward trends in North China, eastern Northeast China and the eastern part of Southwest China, but upward trends in the eastern Tibetan Plateau and some southeastern coastal areas. Two clearly-contrasting regions in climatic changes of wet spells are the mid-lower reaches of the Yellow River and the eastern Tibetan Plateau, characterized by a decrease of about 24 days and an increase of about 6 days in annual wet spell days from 1953 to 2003, respectively.