长江中下游地区骤发干旱与缓发干旱特征对比研究

基于再分析土壤湿度、大气等压面资料以及国际耦合模式比较计划(Coupled Model Intercomparison Project Phase 6,CMIP6)数据,利用大气柱水分收支原理及归因方法,本文识别了1979—2020年长江中下游地区格点骤发干旱与缓发干旱,分析其空间分布及统计特征,并且诊断区域性典型骤发干旱与缓发干旱事件的发展过程及人为因素的影响。结果表明:该区域骤发干旱频发,主要发生在南部,强度偏强,且大多发展于夏季;而缓发干旱发生较少,主要发生在北部,强度偏弱,且大多发展于秋季。大气柱水汽净辐散对两类干旱的发展速度起到了重要作用,骤发干旱在发展过程中大气柱水汽净辐散偏强,造成蒸散发与降水差值较大,使得土壤湿度下降速度快于缓发干旱。2019年夏季长江中下游地区发生了一次大范围的骤发干旱事件,在发展阶段,副热带高压西伸增强了区域大气柱的风场辐散,使大气柱水汽净辐散强,干旱快速发展。2010/2011年发生了一次区域缓发干旱事件,在秋季发展阶段,近地层风场为一弱反气旋环流,风场辐散作用偏弱,大气柱水汽净辐散偏小,使干旱发展速度较慢。人类活动对2019年骤发干旱事件的影响强于2010/2011年缓发干旱事件。

Comparisons on the characteristics of flash drought and slowly-evolving drought in the middle and lower reaches of Yangtze River

Based on the reanalysis of soil moisture, atmospheric isobaric surface data, and CMIP6 model data, the principle of atmospheric column water budget and the attribution method were used to identify the grid flash drought and slowly-evolving drought in the middle and lower reaches of the Yangtze River from 1979 to 2020, moreover, their spatial distribution and statistical characteristics were also analyzed. Furthermore, the development process of regional flash drought and slowly-evolving drought events as well as the influence of human factors were diagnosed. Results show that the flash drought occurrs frequently in the region, mainly in the south areas, with strong intensity, and mostly develops in summer. The slowly-evolving drought occurrs less, mainly in the north areas, with weak intensity, and mostly develops in autumn. The atmospheric column water vapor net divergence plays an important role in the development of the two types of drought. In the development process of flash drought, the atmospheric column water vapor net divergence is stronger, which results in a larger difference between evapotrans￣piration and precipitation, and the decrease rate of soil moisture is faster than the slowly-evolving drought. In the summer of 2019, a large-scale flash drought event occurred in the middle and lower reaches of the Yangtze River. During the development stage, the westward extension of subtropical high enhanced the divergence of wind field in the regional atmospheric column, resulting in strong atmospheric column water vapor net divergence and rapid development of drought. A regional slowly-evolving drought event occurred in 2010/2011. During the autumn development stage, the wind field near the ground layer was a weak anticyclonic circulation. The divergence of wind field was weak, and the atmospheric column water vapor net divergence was small, which led to the slowly-evolving drought. Human activities contributed more to the flash drought event in 2019 than to the slowly-evolving drought event in 2010/2011.