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Spatial Scales of Synchronous Extreme Precipitation in China and Possible Causes
高涛
中国科学院大气物理研究所
Precipitation extremes often appear at surrounding stations simultaneously when reference station experiences extreme rainfall, yielding severe floods. However, the understanding of spatial synchronicity of precipitation extremes in China remains limited. We examine the variability of extreme precipitation synchrony scale (EPSS) during 1961-2014 using a network of 2, 118 meteorological stations. Larger spatial synchronicity of extreme events are mainly located in southwestern regions and northeastern and South China, while the relatively smaller synchrony scales are found in North China Plain, mid-lower reaches of Yangtze River and Sichuan basins. These have a close linkage with elevations with correlation coefficient of 0.33 at the 99% confidence level. Significant increasing trends are seen in central-south China, and northeastern China is dominated by significant declining trends, although national mean synchrony scale exhibits a slight increasing trend. EPSSs tend to be strengthened at most stations during the positive phase of El Niño–Southern Oscillation. And the synchrony scales are expected to be enhanced in North (South) China in the negative (positive) phase of Pacific Decadal Oscillation. Our findings reveal that EPSSs in China are affected by the interaction of complex topography and climate variability. We find that ENSO poses profound influences on extreme precipitation in many portions of China. El Niño (La Niña) intensifies (weakens) the precipitation extremes in southeastern China (SEC) and slightly weakens (intensifies) that in central-north China, mainly by changing the frequency rather than the intensity of extreme precipitation. Further analysis suggests that the East Asian winter monsoon and Siberian high tend to be weaker during El Niño winters, suppressing the southward invasion of cold dry air. Via the weakened Walker circulation, El Niño also triggers anomalously descending motion and anticyclone over the western North Pacific (WNP), which exhibits southwesterly anomalies over SEC and is thus conducive to the transport of sufficient moisture into that area. The changes over WNP are also accompanied by ascending motions over East Asia via a local meridional circulation alike the Pacific-Japan pattern. Meanwhile, El Niño induces a southward-displaced East Asian jet stream, as characterized by intensified westerly over southern China, corresponding to anomalously ascending motion there. Together, these changes facilitate the updrafts of circulations and the condensation of water vapor, thus increasing the occurrence of extreme precipitation in SEC. Moreover, we find that different Niño types exhibit distinct subregional influences. In particular, the canonical eastern Pacific El Niño significantly increases the frequency of extreme precipitation in South China, whereas the Modoki central Pacific El Niño mainly impacts that in East China.Tao Gao1,2, Ming Luo3,4*, Qiang Zhang5* and Ngar‑Cheung Lau4