How Frequently Will the Persistent Heavy Rainfall over the Middle and Lower Yangtze River Basin in Summer 2020 Happen under Global Warming?

Abstract

The middle and lower Yangtze River basin (MLYRB) suffered persistent heavy rainfall in summer 2020, with nearly continuous rainfall for about six consecutive weeks. How the likelihood of persistent heavy rainfall resembling that which occurred over the MLYRB in summer 2020 (hereafter 2020PHR-like event) would change under global warming is investigated. An index that reflects maximum accumulated precipitation during a consecutive five-week period in summer (Rx35day) is introduced. This accumulated precipitation index in summer 2020 is 60% stronger than the climatology, and a statistical analysis further shows that the 2020 event is a 1-in-70-year event. The model projection results derived from the 50-member ensemble of CanESM2 and the multimodel ensemble (MME) of the CMIP5 and CMIP6 models show that the occurrence probability of the 2020PHR-like event will dramatically increase under global warming. Based on the Kolmogorov—Smirnoff test, one-third of the CMIP5 and CMIP6 models that have reasonable performance in reproducing the 2020PHR-like event in their historical simulations are selected for the future projection study. The CMIP5 and CMIP6 MME results show that the occurrence probability of the 2020PHR-like event under the present-day climate will be double under lower-emission scenarios (CMIP5 RCP4.5, CMIP6 SSP1-2.6, and SSP2-4.5) and 3–5 times greater under higher-emission scenarios (3.0 times for CMIP5 RCP8.5, 2.9 times for CMIP6 SSP3-7.0, and 4.8 times for CMIP6 SSP5-8.5). The inter-model spread of the probability change is small, lending confidence to the projection results. The results provide a scientific reference for mitigation of and adaptation to future climate change.

摘要

2020年夏季, 长江中下游地区经历了一次持续性极端降水事件, 区域内日降水量连续近六周维持在较高水平. 本文对类2020年夏季长江中下游持续性极端降水事件发生概率在未来全球变暖背景下的变化进行了定量预估. 首先, 本文利用夏季连续五周最大累积降水量(Rx35day)表征持续性极端降水事件的强度, 结果表明2020年夏季长江中下游Rx35day较1951–2020年气候态偏强60%, 这是一次70年一遇的持续性极端降水事件. 进一步利用CanESM2模式50成员集合和CMIP5、 CMIP6多模式集合进行未来预估, 发现在全球变暖背景下, 类2020年持续性极端降水事件的发生概率将会显著增加. 具体来说, 本文先利用Kolmogorov–Smirnoff检验挑选出能合理再现当今气候背景下类2020年持续性极端降水事件的CMIP模式, 再对这些相对可靠的模式的未来情景模拟结果进行分析, 结果表明: 在低排放情景下(CMIP5 RCP4.5, CMIP6 SSP1-2.6和SSP2-4.5), 类2020年持续性极端降水事件发生概率约为当今气候背景下的2倍; 在高排放情景下, 该风险比率增至3–5倍(CMIP5 RCP8.5为3.0倍, CMIP6 SSP3-7.0为2.9倍, CMIP6 SSP5-8.5为4.8倍). 通过Bootstrap检验发现上述预估结果的不确定性较小, 说明在高排放情景下未来类2020年持续性极端降水事件发生概率很可能显著增加. 该研究结果说明了我国当前积极推广“碳中和”这一重要举措的必要性, 减缓和适应未来气候变化刻不容缓.

Electronic Supplementary Material to

376_2022_1351_MOESM1_ESM.pdf

How Frequently Will the Persistent Heavy Rainfall over the Middle and Lower Yangtze River Basin in Summer 2020 Happen under Global Warming?