Search

The Tibetan Plateau (TP) plays a vital role in Asian and even global atmospheric circulation, through the interactions between land and atmosphere. It has experienced significant climate warming and spatially and temporally variant wetting over the past half century. Because of the importance of land surface status to the interactions, determining the wetting and drying of the TP from individual changes in precipitation (Prep) or temperature is difficult. Soil moisture (SM) is the water synthesis of the surface status. The persistent deficit of SM (SM drought) is more sensitive to climate change than normal SM. This study first explored the climate wetting and drying of the TP from variations in historical SM droughts over 1961–2014, with a focus on spatiotemporal patterns, long-term variations, and climate causes of summer (May–September) SM droughts based on multiple observation and reanalysis data. The results showed comparatively frequent and severe droughts in the central and southern area, particularly in the semiarid and subhumid regions. SM drought exhibited an abrupt and significant (p < 0.05) alleviation in the interior and central-west TP in the middle to late 1990s. The prominent drought alleviation indicated a hydroclimate shift to a wetter plateau, not merely steady trends as given in the literature. We demonstrated that the wetting shift was dominated by Prep over potential evapotranspiration (PET). By contrast, the in-phase trends were combined forces of Prep and PET, with increased forces of PET after the wetting shift. Furthermore, the Prep dominance was largely attributed to a phase transition of the Atlantic multi-decadal oscillation from cold to warm since the mid-1990s. The PET impacts on the wetting trends were likely dominated by solar radiation, wind speed, and vapor pressure deficit. Regionally, the wetting shift was distinct from the arid to semiarid and semiarid to subhumid climate. Such spatiotemporal changes may affect the TP's atmospheric circulation and, subsequently, the Asian monsoon and global circulation, in addition to the fragile ecosystem in the TP. [ABSTRACT FROM AUTHOR]

• The climatological spatial scales (CSS s) of meteorological droughts are investigated. • The CSS s of multi-timescale droughts in China are determined and attributed. • The CSS s generally show a significant decrease with increasing timescale. • The five climate anomalies have significant impacts on the multi-scale CSS s. • The climate anomalies and the CSS s show complex spatiotemporal interaction effects. This study investigates the climatological spatial scales (CSS s) of meteorological droughts in China and the linkages to climate variability. The Global Precipitation Climatology Centre monthly gridded precipitation with a spatial resolution of 25 km × 25 km for 1961–2010 is used. The standardized precipitation index at different timescales (1-, 3-, 6-, 9-, 12-, 24-, 36-, and 48-month) is applied to characterize meteorological droughts. The CSS s of meteorological droughts are calculated using a method considering spatial correlation and anisotropy. The relationships between the CSS s and main monsoons and climate teleconnections in five selected regions are quantified using dynamic spatial panel models. The five regions are South China (SC), the Yangtze River Valley (YRV), North China (NC), Northeast China (NE), and the Tibetan Plateau (TIB). The following results are obtained: (1) The CSS s of multi-timescale meteorological droughts in China are determined. The means of the CSS s at various timescales in China are 68.9, 73.8, 71.8, 69.7, 68.8, 65.9, 62.9, and 60.8 × 104 km2, respectively. The CSS s in eastern China generally show a significant decrease with increasing timescale. (2) Significant quantification relationships (R2 greater than 0.85) suggest that there is not a simple linear relationship between climate anomalies and the CSS s, but rather a complex spatiotemporal interaction including exogenous and endogenous interaction effects. The CSS s not only strongly depend on their neighbors on the same timescale but also significantly depend on the CSS s of neighbors on adjacent timescales. Three monsoon indices (Indian monsoon, East Asian monsoon, and western North Pacific monsoon) have significant impacts on the multi-timescale CSS variations in the five regions, especially for NE, YRV, SC, and TIB, while the El Niño–Southern Oscillation and Pacific Decadal Oscillation affect mainly SC and YRV. These findings could broaden our understanding of the spatiotemporal relationships of droughts and be useful for drought risk management. [ABSTRACT FROM AUTHOR]