华北地区陆气耦合对干旱的影响

Impacts of Land-Atmosphere Coupling on Droughts in North China

摘要: 华北平原是我国重要的粮食主产区与生态脆弱区，干旱灾害频发严重制约区域农业可持续发展与生态安全。以往干旱研究多聚焦大气环流驱动作用，对陆–气耦合过程在干旱发生发展中的影响机制关注不足。本文基于1980~2025年ERA5-Land小时再分析数据，计算1个月、3个月、6个月、12个月尺度标准化降水蒸散指数(SPEI)，结合游程理论识别干旱事件并分析其时空演变特征；通过控制变量敏感性试验量化降水与潜在蒸散对干旱的相对贡献；基于Pearson相关系数对比分析干旱期与非干旱期土壤湿度–温度、土壤湿度–降水的耦合特征差异。结果表明：1个月尺度干旱事件最多，达111次，为华北平原最频发的干旱类型，以单月或双月的季节性短历时干旱为主；3、6个月尺度事件数依次降至54次、38次，长时间尺度通过整合短尺度间断性干旱，使事件集聚性显著增强；12个月尺度干旱事件仅19次，不足1月尺度的1/5，反映区域跨年度持续性极端干旱的发生概率较低；潜在蒸散是华北平原SPEI波动的主导驱动因素，其单独变化可解释大部分的干旱波动，与原始SPEI序列相关系数达0.61，而降水单独变化与原始SPEI相关性很小；干旱期与非干旱期陆气耦合特征存在显著差异，干旱期土壤湿度与2米温度呈弱负相关，“干–热”正反馈机制显著，非干旱期土壤湿度与降水量呈强正相关(平均相关系数0.608)，降水对土壤湿度的补给效率远高于干旱期，干旱期土壤湿度与VPD的负相关强度显著高于非干旱期，反映出干旱期陆气耦合作用的显著增强，蒸散限制因子由水分限制(干旱期)向能量限制(非干旱期)的转变是其核心成因。研究结果可为华北平原干旱监测预警、陆气相互作用机理研究提供科学支撑。

Abstract: The North China Plain (NCP) is a major grain-producing region and an ecologically fragile zone in China, where frequent drought disasters severely constrain the sustainable agricultural development and ecological security of the region. Most previous drought studies have focused on the driving effects of atmospheric circulation, while insufficient attention has been paid to the influencing mechanisms of land-atmosphere coupling processes in the occurrence and development of drought. Based on hourly ERA5-Land reanalysis data from 1980 to 2025, this study calculated the Standardized Precipitation Evapotranspiration Index (SPEI) at 1-month, 3-month, 6-month, and 12-month time scales, identified drought events using the run-length theory, and analyzed their spatiotemporal evolution characteristics. A controlled variable sensitivity experiment was conducted to quantify the relative contributions of precipitation and potential evapotranspiration (PET) to drought. Furthermore, the differences in coupling characteristics of soil moisture-temperature and soil moisture-precipitation between drought and non-drought periods were comparatively analyzed based on Pearson correlation coefficients. The results show that: At the 1-month scale, the number of drought events is the highest, reaching 111, making it the most frequent drought type in the NCP, which is dominated by seasonal short-duration droughts lasting 1 or 2 months. At the 3-month and 6-month scales, the number of events decreases sequentially to 54 and 38, respectively. Longer time scales integrate intermittent short-scale droughts, significantly enhancing the clustering of drought events. At the 12-month scale, only 19 drought events occur, accounting for less than 1/5 of that at the 1-month scale, indicating a low probability of inter-annual persistent extreme droughts in the region. PET is the dominant driving factor of SPEI fluctuations in the NCP: its individual variation can explain almost all drought fluctuations, with a correlation coefficient of 0.61 with the original SPEI series, while the individual variation of precipitation shows almost no correlation with the original SPEI. There are significant differences in land-atmosphere coupling characteristics between drought and non-drought periods. During drought periods, soil moisture shows a weak negative correlation with 2-meter air temperature, and the “dry-hot” positive feedback mechanism is significant. During non-drought periods, soil moisture exhibits a strong positive correlation with precipitation (average correlation coefficient: 0.608), and the replenishment efficiency of precipitation to soil moisture is much higher than that during drought periods. In addition, the intensity of the negative correlation between soil moisture and Vapor Pressure Deficit (VPD) is significantly higher in drought periods than in non-drought periods, indicating a significant enhancement of land-atmosphere coupling during drought periods. The core cause of this difference is the shift of the evapotranspiration limiting factor from water limitation (during drought periods) to energy limitation (during non-drought periods). The findings of this study can provide scientific support for drought monitoring and early warning, as well as research on the mechanism of land-atmosphere interaction in the North China Plain.