2005—2017年两次强ENSO事件对中国区域陆地水储量变化影响的卫星重力观测

近年来极端气候事件的频发对全球和区域性水循环产生了重大影响,特别是2005—2017年间两次强ENSO(El Nino-Southern Oscillation)事件使得全球陆地水储量出现了较大的年际波动.GRACE(Gravity Recovery and Climate Experiment)重力卫星随着数据质量的提高、后处理方法的完善和超过十年的连续观测,捕捉陆地水储量异常的能力明显提高,这为研究2005—2017年间两次强ENSO事件对中国区域陆地水储量变化的影响提供了观测基础.本文综合利用GRACE卫星重力数据、GLDAS水文模型和实测降水资料分析了中国区域陆地水储量年际变化和与ENSO的关系.研究发现:长江流域中、下游地区和东南诸河流域与ENSO存在较高的相关性,与ENSO的相关系数最大值分别为0.55、0.78、0.70,较ENSO分别滞后约7个月、5个月和5个月.其中长江流域下游地区与ENSO的相关性最强,2010/11 La Nina和2015/16 El Nino两次强ENSO事件使得陆地水储量分别发生了约-24.1亿吨和27.9亿吨的波动.在2010/11 La Nina期间,长江流域下游地区和东南诸河流域陆地水储量异常约在2011年4—5月达到谷值,而长江流域中游地区晚1~2月达到谷值.在2015/16 El Nino期间,长江流域中、下游地区和东南诸河流域陆地水储量从2015年9月到2016年7月持续出现正异常信号.其中,2015年秋冬季(2015年9月至2016年1月)陆地水储量异常明显是受此次El Nino同期影响的结果;2016年春季(4—5月)陆地水异常是受到此次厄尔尼诺峰值的滞后影响所致;2016年7月的陆地水储量异常则与西北太平洋存在的异常反气旋环流有关.

Effects of two strong ENSO events on terrestrial water storage anomalies in China from GRACE during 2005-2017

In recent years, the frequent occurrence of extreme climate events has had a great impact on the global and regional water cycle, of which two strong El Niño-Southern Oscillation (ENSO) events from 2005 to 2017 have caused significant inter-annual fluctuations of terrestrial water storage (TWS). With the improvement of data quality, the advancement of post-processing methods and the persistence of observations more than one decade, the Gravity Recovery and Climate Experiment (GRACE) twin satellites can be used to monitor long-term terrestrial water storage anomalies (TWSA) accurately, which makes it possible to study the correlation between TWSA and ENSO events. Here we estimate TWSA from GRACE, soil moisture storage anomalies (SMSA) from Global Land Data Assimilation System (GLDAS) models, and precipitation anomalies in main river basins of China and quantify their correlations with ENSO events. This study shows that, among main river basins of China, the typical ENSO-related regions are located in the middle and lower reaches of Yangtze River Basin (YRB) and the Southeastern River Basin (SRB), with maximum correlation coefficients between TWSA and ENSO of 0.55, 0.78 and 0.70, respectively. The TWSA in these three typical ENSO-related regions lag behind ENSO by ~7 months,~5 months,~5 months, respectively. Among them, ENSO has the greatest impact on the lower reach of YRB. During the two strong ENSO events (i.e, 2010/11 La Niña and 2015/16 El Niño), the magnitude of TWS fluctuations reaches -24.1 Gt and 27.9 Gt, respectively. During the 2010/11 La Niña period, TWSA over the lower reach of YRB and the SRB reach the minimum around April to May 2011; while the minimum of TWSA over the middle reach of YRB happened 1-2 months later. During the 2015/16 El Niño period, TWS increased continuously in the middle and lower reaches of YRB and the SRB, due to continuous El Niño from autumn-winter of 2015 to early 2016. Another two anomalies in TWS in April-May of 2016 and July 2016 are related to the lagging effect of 2015/16 El Niño, which are caused by the lagging effect of the persistent abnormal anticyclonic circulation in the western North Pacific. It is demonstrated that GRACE has an unprecedented superiority in detecting the correlations between TWSA and ENSO.