中国旱涝骤变事件的变化特征及影响因子研究

In recent years,the 'Abrupt Change between Drought and Flood ' has gradually attracted people's attention,the event is a special category of extreme weather events,that be increased by climate change. At present, the research results in this field are relatively few.In this project, concept of ‘Abrupt Change between Drought and Flood’ will be proposed and then daily index for these phenomena will be conducted, after that, a technique to recognize drought-flood abrupt change events would be developed according to‘identification technique of regional extreme events ’. Building a long time sequence of the events ,that about 'Abrupt Change between Drought and Flood' in the past 60 years in China.On above basis, we would study climatic changing law for frequency, intensity of drought-flood abrupt change events, analyze relationship between meteorological elements before the abrupt change and features of drought (flood) events after the abrupt change, such as intensity and duration. At the same time, revealing the cause of drought-flood abrupt change events on aspects of general atmospheric circulation and outside forces. Finally, prediction model for features of drought (flood) events which is after the abrupt change would be presented.The innovations of this project include the concept and the index of the 'Abrupt Change between Drought and Flood', and long time sequence of the events about 'Abrupt Change between Drought and Flood'.This project will make an important supplement and expansion to the research of the disastrous weather and climate events in China.The expected achievements would helpful for improving the technical level on monitoring, predicting and warning of abrupt change events.

旱涝骤变事件是极端气候事件的一个特殊类别，气候变化加剧了这类事件的发生，近年来才逐渐引起注意，鲜有相关成果。本项目首先提出“旱涝骤变事件”概念并构建旱涝骤变指数，给出旱涝骤变事件的定量化定义；结合“区域性极端事件客观识别方法”发展旱涝骤变事件的判别技术，构建我国旱涝骤变事件近60年的时间序列。其次，研究旱涝骤变事件的气候变化特征，分析事件发生频率、强度等要素的变化规律和空间分布特征，分析前期气候异常特征与同期和后期旱涝骤变事件的强度和持续时间等特征之间的关系，从大气环流及外源强迫等方面揭示旱涝骤变事件的成因，提出影响骤变事件的强信号特征及其预测概念模型。本项目在旱涝骤变事件概念、骤变指数、长时间序列等方面的研究具有创新性，将是对我国灾害性天气气候事件研究的重要补充和拓展，对提高急转型气象灾害事件的监测、预测和预警技术水平有重要意义。

旱涝骤变事件是短期内发生的旱、涝之间急剧转折事件。在气候变化的大背景下，旱涝骤变事件作为极端气候事件的一个特殊类别，逐渐引起了关注。这种急转型灾害过程中会出现极端事件类型的突然转变，因此极易在缺乏预警和防范意识的情况下造成比单独的极端事件更严重的社会经济损失。为了更全面深入地掌握旱涝骤变事件的发生规律和基本特征，本项目在给出“旱涝骤变事件”定义的基础上，构建旱涝骤变的定量化判别指数，研究旱涝骤变事件的气候变化特征及持续性特征，分析典型旱涝骤变过程中致涝强降水的水汽源及触发机制，并从大气环流等方面研究相关事件过程的影响因素。同时，对沙漠地区旱涝急转过程开展了综合野外观测试验。结果表明，旱涝骤变事件主要包括两类：旱涝急转事件和涝旱转折事件。中国北方地区旱涝骤变事件发生频次和强度都较大的区域位于青海南部和东北部、陕西南部、河北北部、辽宁和吉林东南部、黑龙江大部。同时，这些事件的发生具有明显的季节性，旱涝急转事件在夏季的发生频次较高，而涝旱转折事件在春末夏初的发生频次较高。本世纪以来，涝旱转折事件的发生频次较之前的时段偏多。中国大部分旱涝骤变事件的持续时间主要以旱、涝分别持续1个月的组合为主。这种持续时长的旱涝急转事件主要出现在中国东部和南部地区，而涝旱转折事件主要出现在中国中部、西南和东北地区。旱涝骤变过程中强降水的形成主要是由大尺度环流因子、水汽输送、地形抬升等要素共同作用并触发的。基于野外观测试验数据，确定了沙漠地区旱涝急转过程的总体输送系数、地表反照率、土壤热传导率、粗糙度长度、边界层高度等陆面过程和大气边界层主要物理参数。本项目成果对提高极端气候事件的监测和预警技术水平有重要意义。