Projected relationship between ENSO and following-summer rainfall over the middle reaches of the Yangtze River valley based on CMIP6 simulations

Abstract

El Niño–Southern Oscillation (ENSO) events have a strong impact on the middle reaches of Yangtze River summer rainfall (YRSR). The authors project how this impact might vary in the future. As in the historical period of 1979–2014, the middle reaches of the Yangtze River are projected to experience positive (negative) precipitation anomalies in post-El Niño (post-La Niña) summers in 2015–2100 under SSP5-8.5, and three related physical processes—namely, ENSO–tropical Indian Ocean (TIO) sea surface temperature (SST), TIO SST–Philippine Sea convection (PSC), and PSC–YRSR relationships—continue to have an impact. First, because the above three processes are projected to be significant, the ENSO–YRSR relationship is significant at the 90% confidence level over most periods of 2015–2100 under SSP5-8.5, according to the median of five reasonable CMIP6 models and the median of 20 reasonable EC-Earth3 runs. Second, due to the aforementioned three stronger relationships, the ENSO–YRSR relationship is projected to be somewhat stronger in 2015–2100 than in 1979–2014, based on both the median of all 30 CMIP6 models and the median of all 56 EC-Earth3 runs. Third, the ENSO–YRSR relationship projected by the median of five reasonable models remains stronger than that projected by the median of all CMIP6 models, owing to the former's stronger TIO SST–PSC and PSC–YRSR relationships under SSP5-8.5. Additionally, future assessments of uncertainty of projections in ENSO–YRSR relationship are still necessary.

摘要

厄尔尼诺—南方涛动 (ENSO) 对长江中游夏季降水 (YRSR) 的年际变化影响较大. 基于CMIP6模式数据, 本文预估了未来ENSO与长江中游夏季降水关系的变化. 与1979∼2014年相似, SSP5-8.5高排放情景下ENSO−YRSR的关系仍表现为前冬发生厄尔尼诺 (拉尼娜) 后, 长江中游夏季降水为正异常 (负异常). 同时, 仍然受三个物理过程影响:前冬ENSO影响次年夏季印度洋海温 (ENSO−TIO SST), 印度洋海温异常进而影响菲律宾对流 (TIO SST−PSC) , 菲律宾对流对长江中游夏季降水产生影响 (PSC−YRSR). 例如, (1) 5个CMIP6好模式的中位数和20个EC-Earth3好子集的中位数均预估ENSO−YRSR在2015∼2100年大部分时段保持显著正相关关系, 因为上述三个物理过程的相关关系在未来也显著. (2) 30个CMIP6模式的中位数和56个EC-Earth3子集的中位数预估ENSO−YRSR关系略有增强; 主要是因为上述三个物理过程在未来变强. (3) 5个CMIP6好模式的中位数预估ENSO−YRSR关系仍强于30个CMIP6模式的中位数结果, 主要是因为前者预估的TIO SST−PSC和PSC−YRSR关系更强. 未来将关注ENSO−YRSR预估的不确定性来源.