中国春季极端旱涝急转事件时空分布特征研究

Spatiotemporal Distribution Characteristics of Extreme Drought-Flood Whiplash Events in China in Boreal Spring

摘要: 目前，针对旱涝急转事件的判定尚缺乏统一的指标体系。为克服现有气象干旱指数在春季持续性旱涝研究中存在的全国范围可比性不足、季节针对性欠缺及物理意义不清晰等问题，并填补春季极端强度旱涝急转事件研究的空白，本文基于1971~2020年中国地面气象台站逐日降水资料，构建了适用于表征春季持续性旱涝异常的春季持续性旱涝指数(spring persistent drought-flood index, SPDFI)。在此基础上，采用旋转经验正交函数进行客观分区，识别出春季旱涝关键区域；依据SPDFI进一步定义春季极端旱涝急转事件的识别标准，系统识别了1971~2020年间黄淮与江南两个春季旱涝核心区域发生的所有具有极端强度的旱涝急转事件，并分析了其时间变化特征。结果表明：中国春季存在黄淮、江南、西北和华北四个旱涝关键区，其中黄淮与江南区域方差贡献最大，是中国春季持续性旱涝异常的核心区域。频域分析结果显示，在季节内尺度(10~90天)上，黄淮区域降水异常的显著信号集中于10~20天准双周频段，而江南区域则以30~60天低频振荡为主。这一差异表明两者可能分别受中高纬度系统与热带/副热带系统的主导调控。两区域春季极端旱涝急转事件的统计结果显示，黄淮区域两类事件表现出明显的季节锁相特征，这可能与降水气候态季节内振荡有关。此外，两区域事件在发生时间上基本相互独立，未表现出同步性。本文构建的SPDFI及极端旱涝急转事件识别方法，为中国春季旱涝急转研究提供了新的分析工具与区域划分框架，研究结果可为深入理解中国春季极端旱涝急转的物理机理奠定基础，相关影响机制有待进一步研究。

Abstract: At present, a unified index system for identifying drought-flood whiplash events remains lacking. To address the limitations of existing meteorological drought indices in studying persistent spring droughts and floods—namely insufficient nationwide comparability, lack of seasonal specificity, and ambiguous physical implications—and to fill the gap in research on extreme-intensity drought-flood whiplash events in boreal spring, this study constructs a Spring Persistent Drought-Flood Index (SPDFI) based on daily precipitation data from surface meteorological stations across China for the period 1971~2020. The SPDFI is specifically designed to characterize persistent spring drought and flood anomalies. On this basis, rotated empirical orthogonal function (REOF) analysis is employed for objective regionalization, identifying key regions of spring drought and flood variability. Using the SPDFI, a set of criteria is further established to define extreme spring drought-flood whiplash events. All such extreme-intensity whiplash events occurring between 1971 and 2020 in the two core regions—the Huang-Huai region and the Jiangnan region—are systematically identified, and their temporal characteristics are analyzed. The results reveal four principal drought-flood variability regions in China during boreal spring: Huang-Huai, Jiangnan, Northwest China, and North China. Among these, the Huang-Huai and Jiangnan regions exhibit the largest variance contributions, establishing them as the core areas of persistent spring drought and flood anomalies in China. Frequency-domain analysis shows that, on the intraseasonal timescale (10~90 days), significant signals of precipitation anomalies in the Huang-Huai region are concentrated in the quasi-biweekly band of 10~20 days, whereas the Jiangnan region is dominated by low-frequency oscillations of 30~60 days. This contrast implies that the two regions are primarily governed by mid-to-high latitude systems and tropical/subtropical systems, respectively. Statistical results for extreme spring drought-flood whiplash events in the two regions indicate that events in the Huang-Huai region exhibit a pronounced seasonal phase-locking feature, which may be related to the climatological intraseasonal oscillation of precipitation. In addition, the timing of events in the two regions is largely independent, showing no notable synchronicity. The SPDFI and the identification methodology for extreme drought-flood whiplash events developed in this study provide a new analytical tool and regionalization framework for research on spring drought-flood transitions in China. The findings lay a foundation for a deeper understanding of the physical mechanisms underlying extreme spring drought-flood whiplash events in China, though the associated influencing mechanisms warrant further investigation.