人為影響對梅雨極端降雨變化的歸因分析

Abstract

人為因子為氣候變遷的主要作用力，其對於極端降雨天氣系統的影響，為全球暖化趨勢下人們在所關注的議題。本研究利用雲解析風暴模式(CReSS)，選擇2012年6月10至12日以及2017年6月2至3日的梅雨鋒面極端降水個案進行模擬和分析。控制實驗(CE)分別使用ECMWF ERA5、NCEP CFSv2、NCEP FNL、NASA Goddard MERRA-2以及JMA JRA-55等五種不同分析(或再分析)資料做為初始與邊界條件進行模擬並比較差異。敏感度實驗(SE)則使用2000-2014年5-6月CMIP6歷史情境模擬和自然情境模擬的差值，估計過去到近代人為因子所累積造成的氣候背景變化，並將其由與控制實驗相同的初始與邊界條件中扣除再進行模擬。由於控制實驗和敏感度實驗之間的差異可視為人為因子影響的強迫造成的影響，因此藉由梅雨鋒面極端降雨及結構等變化，可以分析過去氣候變遷中人為因子的貢獻。研究結果顯示由於鋒面結構與演變複雜，伴隨的降雨亦具有高度的非線性，因此在受人為因子影響的暖化情境下，對於區域降雨量增減的探討，不能僅考慮對流增強，還需考量環境場、鋒面位置變動與對流胞生命期等多重的因素。此外，透過水收支分析，梅雨鋒面個案受到人為因子影響的降水過程中，主要受鋒面影響的北部區域，對流水氣輻合的增強為總降水量的主因；而主要受西南氣流影響的南部區域，總降水量則伴隨著西南氣流的減弱而降低。整體降水增減的特徵出現了較明顯的南北區域差異，也體現了強降雨增強、弱降雨減弱的趨勢。Anthropogenic factors are the primary driver of climate change, with their impact on extreme rainfall systems being a key concern in global warming trends. This study employs the Cloud-Resolving Storm Simulation (CReSS) model to simulate and analyze two Mei-yu front extreme precipitation cases: June 10-12, 2012 and June 2-3, 2017. Control experiments (CE) used five different reanalysis datasets (ECMWF ERA5, NCEP CFSv2, NCEP FNL, NASA Goddard MERRA-2, and JMA JRA-55) as initial and boundary conditions to compare simulation differences. Sensitivity experiments (SE) utilized CMIP6 historical and natural scenario simulations from 2000-2014 (May-June) to estimate climate background changes caused by anthropogenic factors, incorporating the same initial and boundary conditions as the control experiments.Research findings reveal that due to the complex frontal structure and nonlinear precipitation characteristics, warming scenarios influenced by anthropogenic factors cannot solely consider convection enhancement. Multiple factors, including environmental conditions, frontal position shifts, and convective system lifespans, must be examined. Furthermore, in the Mei-Yu front cases, the northern region—primarily influenced by the front—showed increased precipitation due to enhanced convective vapor convergence. Conversely, the southern region, influenced by southwesterly wind, experienced reduced precipitation with weakening southwestern winds. The overall precipitation pattern demonstrated pronounced north-south regional differences, reflecting a trend of intensified heavy rain and reduced light rain.