Variations of dryness/wetness across China: Changing properties, drought risks, and causes

- New findings concerning regionalization of drought hazards;
- New light on shortening periodicity of drought processes;
- Novel interpretation of drought occurrences from moisture propagation;
- Identification of intensifying and/or amplifying droughts in different parts of China.

Variations of wetness/dryness across China during 1949-2014 in both space and time were investigated using the grid climate data of Time-Series (TS) Version 3.23. The Standardized Precipitation Evapotranspiration Index (SPEI) was used to evaluate the wetness and dryness conditions. Results indicated that the regions that experienced a drying/wetting tendency are similar in area, and the regions dominated by a drying tendency are east of 100°E and the regions experiencing a wetting tendency are west of 100°E. A significant wetting tendency was observed in the northern parts of northwestern China, Qaidam Basin and northeastern parts of the Tibetan Plateau. Analysis of water vapor flux by air mass propagation indicated that dry regimes are attributed to continental air mass and wet regimes to oceanic air mass. Propagation of water vapor flux can thus explain the occurrence of wetness/dryness events in both space and time. The shortening of periodicity or increased frequency of wet and/or dry regimes implies intensifying and amplifying wet and dry regimes across China. The results of this study would be useful for the management of agricultural irrigation and water resources across China in a changing environment.