全球变暖背景下华西秋雨的演变规律及与极区气候系统变化的联系

Climate change and resultant disasters are highly concerned by the scientific community and decision makers. As a high-impact climate phenomenon, autumn rain in West China poses a serious threat to the social economy and the safety of life and property. Therefore, study on the change of autumn rain in West China and the related physical mechanism in the context of global warming owes important scientific value and application value. However, previous studies on the autumn rain in West China focused mainly on the seasonal and interannual time scales, and paid little attention to its secular change and associated physical mechanism, which greatly constrains our understanding of the evolution characteristic of autumn rain in West China as well as corresponding physical mechanisms. Thus, this project is motivated to study the long-term change of autumn rain in West China following the idea of observed change-process understanding-future projection. That is, using the observation data and the model simulation data, this study will identify the observed secular changes of autumn rain in West China under the background of global warming, and further explore the roles of polar climate system (including Antarctic Oscillation, Arctic Oscillation, Antarctic sea ice and Arctic sea ice) played in the interdecadal change of autumn rain in West China and the corresponding physical mechanisms. Combing global model simulations with downscaling simulations of the regional model, this study will also project future change of autumn rain in West China. Through this study, it is expected to provide key new knowledge for the understanding of the secular change of autumn rain in West China and the related physical mechanism, and provide scientific support for climate change adaptation as well as disaster prevention and mitigation.

气候变化及其造成的灾害倍受科学界和决策者的高度关注。华西秋雨作为我国西部地区秋季出现的一种高影响气候现象，严重威胁社会经济和生命财产安全。因此，深入研究全球变暖背景下华西秋雨的变化规律和机理具有重要的科学价值和实际应用价值。然而，以往关于华西秋雨的研究大都集中于季节尺度和年际尺度上，对华西秋雨的长期变化与机理鲜有涉及，极大地限制了对华西秋雨变化规律和机理的理解。基于此，本项目以华西秋雨长期变化为出发点，以变化事实-过程机理-未来预估为研究思路，通过观测资料和模式资料分析，明晰当前全球变暖背景下华西秋雨的变化特征，探讨极区气候系统（如，南极涛动、北极涛动、南极海冰、北极海冰）变化对华西秋雨年代际变化的作用和相应的物理机制；采用全球模式和区域模式动力降尺度相结合，综合预估华西秋雨的未来演变规律，以期为理解华西秋雨长期变化与机理提供关键性新认识，为我国适应气候变化和防灾减灾提供科学支撑。

华西秋雨作为我国中西部地区秋季出现的一种高影响气候现象，严重威胁社会经济和生命财产安全。因此，深入研究全球变暖背景下华西秋雨的变化规律和机理具有重要的科学价值和实际应用价值。本项目基于观测资料和模式数据，研究了华西秋雨在不同时间尺度上的变化与物理机制，预估了其未来变化。. 研究揭示：1）1961年以来，华西区域平均的秋雨量和降水日数呈减少而强度呈增强的线性趋势。空间上，秋雨量在华西东部减少而在西部增加，与水汽输送和大气稳定性的趋势变化密切相关。2）华西秋雨趋势变化在1990年代末发生了由减少向增多的年代际转折，与巴尔喀什湖槽加深、东亚西风急流偏北、向华西的水汽输送增强、印度洋和大西洋西部海温变暖密切相关。3）秋季北极涛动（AO）与华西东部降水的联系在1980年代中期后加强。后一段时间里，AO偏强对应巴尔喀什湖槽加深、东亚沿岸气压升高，华西为异常上升运动，利于降水发生。AO与华西秋雨关系的加强可能源于更强的波动能量传至北太平洋，从而加强AO与北太平洋大气环流的联系。4）夏季南印度洋和南太平洋海冰与华西秋季降水呈显著正相关。夏季南印度洋和南太平洋海冰偏多时，随后秋季巴尔喀什湖槽加深，东亚西风急流偏北，向华西的水汽输送增强，利于降水增加。夏季海冰异常引起的南印度洋和南太平洋高纬高空环流异常可从夏季维持到秋季，进而通过印度洋和太平洋上空的遥相关引起欧亚环流异常；对流层低层的南半球环流则与向华西的水汽输送相联。5）巴尔喀什湖槽与赤道中太平洋海温的协同对华西秋雨年际多寡变化具有指示意义。巴尔喀什湖槽加深，配以赤道中太平洋冷海温，最利于华西秋雨偏多。6）未来变暖背景（RCP4.5）下，到21世纪末期，降雨量和日数在华西西北部增加而在东南部减少。西北部降水增多与纬向水汽输送和大气不稳定度增加有关；经向和纬向水汽输送减弱则造成东南部降水减少。这些成果为理解华西秋雨变化与机理提供了新认识，也为适应气候变化和防灾减灾奠定了科学基础。