江淮流域极值降水发生时间的特征及其与区域水分循环变异的关系

The rain belt has moved southward and northward for three times in eastern China since the 1950s. What kind of variation did the water cycle system (WCS) undergo and what characteristics did the extreme precipitation have during different periods under such kind of background in the Jianghuai Basin? Currently, the research on the timing of extreme precipitation (TEP) is relatively rare and the mechanisms of the impacts of the process and variation of WCS on extreme precipitation is not clear. Besides, the influences of TEP changes on the coincidence probability of rainstorms and floods are not well understood. This study attempts to investigate how the variation of WCS influences the changes of TEP in the Jianghuai Basin, and further influences the laws of rainstorm and flood occurrence based on the interdisciplinary analysis of hydrology and meteorology. First, the characteristics of TEP will be analysed, and the characters of timing and intensity will be explored together. Second, the relationship between TEP and regional WCS variation will be investigated. The process and variation of WCS will be diagnosed, the atmospheric process model of water cycle will be built up, and the statistical model of key factors of WCS variation and TEP will be obtained with the help of the circulation type analysis, thus shedding light on the mechanisms of TEP changes. Thirdly, the coincidence probability model will be built up based on Copula function, and the impacts of TEP on the coincidence probability of rainstorms and floods in the Jianghuai Basin will be discussed, which will be helpful for the estimation of the flood disaster risk in the basin.

1950年代以来我国雨带发生了3次南北转移，此背景下江淮流域的水分循环系统经历了何种变异，极值降水在各阶段有何特征？当前关于极值降水发生时间方面的研究不足，水分循环系统的动态和变异对极值降水的影响机制不太明晰，极值降水发生时间变化引起的暴雨洪水遭遇组合的概率改变也不太清楚。本研究从水文和气象学科交叉的角度，探索江淮流域水分循环系统的变异如何驱动极值降水发生时间的变化，进而影响暴雨洪水的发生规律。首先分析极值降水发生时间的特征，将其发生时间和强度进行综合分析；其次探讨极值降水发生时间变化与区域水分循环变异的关系，诊断水分循环系统的动态和变异，构建水分循环的大气过程模型，借助环流型的分析建立水分循环系统变异的关键指标与极值降水发生时间之间的统计模型，揭示其影响机制；最后基于Copula函数建立遭遇概率模型，探讨极值降水发生时间变化对江淮流域暴雨洪水遭遇组合的影响，从而更准确评估流域洪灾的风险。

当前关于极值降水发生时间方面的研究十分不足，区域水分循环对极值降水演变特征的影响机制尚不明晰。本研究从水文和气象学科交叉的角度，通过统计分析、极值模拟、气候诊断、水汽分析等方法，刻画江淮流域极值降水发生时间的时空特征，探求极值降水演变与区域水分循环变异、大气环流之间的联系，以及极值降水发生时间变化引起的暴雨洪水遭遇组合的概率。主要成果包括：（1）淮河流域极端降水发生时间的第一模态呈“西北-东南”反位相分布，第二模态呈一致性分布，多数站点发生时间呈微弱提前趋势；江淮地区全年与夏季极端降水平均发生时间的空间分布相似，主要表现为由南向北推迟的特征，冬季则表现为从四周向中部推迟。（2）夏季江淮地区作为水汽汇的情况下，依然能通过瞬变水汽向北方输送水汽，在秋季和冬季，瞬变水汽与平均水汽的收支具有相同的量级。（3）西太平洋反气旋的强弱会影响印度洋-南海一带水汽与西太平洋水汽交汇的位置，进而影响到各海域对研究区的水汽输送路径和贡献大小。（4）未来气候情景下饶河流域两个支流洪涝发生的遭遇概率：对发生日期，遭遇概率在未来会下降，而发生日期会提前；对量级，子流域遭遇概率和自身发生概率均下降。（5）在弱EASM年，淮河流域极端降水的强弱主要与WPSH的强度有关，在强EASM年，其强弱主要与WPSH的位置有关。（6）前期青藏高原东部大气热源变化对后期南亚高压强度变化具有显著影响，从而影响到江淮梅雨区极端降水的强弱变化。研究成果可增进江淮流域洪涝灾害发生机理方面的认识，为区域防洪减灾提供借鉴。共发表研究论文21篇，其中SCI论文10 篇，核心期刊论文10篇；发表在《Geophysical Research Letters》、《International Journal of Climatology》、《Atmospheric Research》、《高原气象》为代表的国内外主流大气科学类、水文科学类学术期刊上。