Global aridification in the second half of the 20th century and its relationship to large-scale climate background

The variation in surface wetness index (SWI), which was derived from global gridded monthly precipitation and monthly mean surface air temperature datasets of Climatic Research Unit (CRU), from 1951 2002 over global land was analyzed in this paper. The characteristics of the SWI variation in global continents, such as North America, South America, Eurasia, Africa, and Australia, were compared. In addition, the correlation between the SWI variation of each continent (or across the globe) and the large-scale background closely related to SST variations, which affects climate change, was analyzed. The results indicate that the SWI variation shows distinct regional characteristics in the second half of the 20th century under global warming. A drying trend in the last 52 years occurred in Africa, Eurasia, Australia and South America, most obviously in Africa and Eurasia. North America shows a wetting trend after 1976. A 30-year period of dry-wet oscillation is found in South America and Australia; the latest is in a drying period in two regions. The results also revealed that global warming has changed the dry-wet pattern of the global land. South America and Australia have a drying trend despite increases in precipitation. This indicates that increases in surface air temperature cannot be ignored in aridification studies. Global dry-wet variation is closely related to large-scale SST variations: the drying trend in Africa and Eurasia and the wetting trend in North America are correlated with Pacific Decadal Oscillation (PDO); the interdecadal oscillation of SWI in South America and Australia is consistent with the interdecadal variation in Southern Oscillation Index (SOI).