Drought intensity is commonly characterized using meteorologically-based metrics that do not provide insight into water deficits within deeper hydrologic systems. In contrast, global positioning system (GPS) displacements are sensitive to both local and regional hydrologic-storage fluctuations. While a few studies have leveraged this sensitivity to produce geodetic drought indices, hydrologic drought characterization using GPS is not commonly accounted for in drought assessment and management. To motivate this application, we produce a new geodetic drought index (GDI) and quantify its ability to characterize hydrologic drought conditions in key surface and sub-surface hydrologic reservoirs/pools across California. In northern California, the GDI exhibits a strong regional association with surface-reservoir storage at the 1-month time scale (correlation coefficient: 0.83) and groundwater levels at the 3-month time scale (correlation coefficient: 0.87), along with moderate associations with stream discharge at the daily (instantaneous) time scale (correlation coefficient: 0.50). Groundwater in southern California is best characterized with a 12-month GDI (correlation coefficient: 0.77), and surface-reservoir storage is optimized with the 3-month GDI (correlation coefficient: 0.72). Two sigma uncertainties are ±0.03. Differences between northern and southern California reveal that the GDI is sensitive to unique aquifer and drainage basin characteristics. In addition to capturing long-term hydrologic trends, rapid changes in the GDI initiate during clusters of large atmospheric river events that closely mirror fluctuations in traditional hydrologic and meteorological observations. We show that GPS-based hydrologic drought indices provide a significant opportunity to improve drought assessment, in California and beyond, by improving our understanding of the hydrologic cycle.

中文翻译：

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利用 GPS 描述干旱特征：深入了解加利福尼亚州地下水和地表水库储存


干旱强度通常使用基于气象的指标来表征，但这些指标无法深入了解更深层次水文系统中的缺水情况。相比之下，全球定位系统（GPS）位移对当地和区域水文蓄水波动都很敏感。虽然一些研究利用这种敏感性来产生大地测量干旱指数，但在干旱评估和管理中通常不考虑使用 GPS 进行水文干旱特征描述。为了推动这一应用，我们制定了新的大地干旱指数 (GDI)，并量化其表征加州关键地表和地下水库/水池水文干旱条件的能力。在加利福尼亚州北部，GDI 与 1 个月时间尺度的地表水库蓄水量（相关系数：0.83）和 3 个月时间尺度的地下水位（相关系数：0.87）表现出很强的区域关联，同时也存在中等关联每日（瞬时）时间尺度的河流流量（相关系数：0.50）。南加州地下水最好用 12 个月的 GDI（相关系数：0.77）来表征，地表水库储存则用 3 个月的 GDI（相关系数：0.72）进行优化。两个 sigma 不确定度为 ±0.03。加州北部和南部之间的差异表明，GDI 对独特的含水层和流域特征很敏感。除了捕捉长期水文趋势外，GDI 的快速变化是在大型大气河流事件集群期间启动的，这些事件密切反映了传统水文和气象观测中的波动。 我们表明，基于 GPS 的水文干旱指数通过提高我们对水文循环的了解，为改善加利福尼亚州及其他地区的干旱评估提供了重要机会。