Department of Civil and Environmental Engineering, and Center for Environmental Sciences and Engineering, University of Connecticut, Storrs, CT, 06269.
Proc Natl Acad Sci U S A. 2022 Aug 9;119(32):e2202767119. doi: 10.1073/pnas.2202767119. Epub 2022 Aug 1.
Flash drought often leads to devastating effects in multiple sectors and presents a unique challenge for drought early warning due to its sudden onset and rapid intensification. Existing drought monitoring and early warning systems are based on various hydrometeorological variables reaching thresholds of unusually low water content. Here, we propose a flash drought early warning approach based on spaceborne measurements of solar-induced chlorophyll fluorescence (SIF), a proxy of photosynthesis that captures plant response to multiple environmental stressors. Instead of negative SIF anomalies, we focus on the subseasonal trajectory of SIF and consider slower-than-usual increase or faster-than-usual decrease of SIF as an early warning for flash drought onset. To quantify the deviation of SIF trajectory from the climatological norm, we adopt existing formulas for a rapid change index (RCI) and apply the RCI analysis to spatially downscaled 8-d SIF data from GOME-2 during 2007-2018. Using two well-known flash drought events identified by the operational US Drought Monitor (in 2012 and 2017), we show that SIF RCI can produce strong predictive signals of flash drought onset with a lead time of 2 wk to 2 mo and can also predict drought recovery with several weeks of lead time. While SIF RCI shows great early warning potential, its magnitude diminishes after drought onset and therefore cannot reflect the current drought intensity. With its long lead time and direct relevance for agriculture, SIF RCI can support a global early warning system for flash drought and is especially useful over regions with sparse hydrometeorological data.
闪蒸干旱通常会对多个部门造成破坏性影响，由于其突然发生和快速加剧，给干旱预警带来了独特的挑战。现有的干旱监测和预警系统基于各种水文气象变量达到异常低含水量的阈值。在这里，我们提出了一种基于星载太阳诱导叶绿素荧光（SIF）测量的闪蒸干旱预警方法，SIF 是光合作用的一个代理，可捕捉植物对多种环境胁迫的反应。我们关注的不是负 SIF 异常，而是 SIF 的亚季节轨迹，并将 SIF 增加缓慢或减少过快视为闪蒸干旱开始的预警。为了量化 SIF 轨迹与气候常态的偏差，我们采用了现有的快速变化指数（RCI）公式，并将 RCI 分析应用于 2007-2018 年 GOME-2 的空间降尺度 8 天 SIF 数据。使用美国干旱监测机构（2012 年和 2017 年）确定的两个著名的闪蒸干旱事件，我们表明 SIF RCI 可以产生强烈的闪蒸干旱开始的预测信号，提前时间为 2 周到 2 个月，并且可以提前数周预测干旱的恢复。虽然 SIF RCI 显示出巨大的预警潜力，但它的幅度在干旱发生后会减弱，因此不能反映当前的干旱强度。由于其较长的提前期和与农业的直接相关性，SIF RCI 可以支持闪蒸干旱的全球预警系统，特别是在水文气象数据稀疏的地区非常有用。
