We study vertical ground displacement time series from Global Navigation Satellite System (GNSS) stations to measure deformation associated with hydrological drought in the Po river basin. Focusing on interannual trend changes, rather than seasonal (annual) components, we found a clear spatially correlated deformation signal that is temporally (anti)correlated with changes in the Po river level and the SPEI-12 drought index, with stations moving upward during periods of river/index level decrease and vice versa. In the 2021–2022 time span, which culminated in the most severe drought of the last two centuries, we estimate the amount and spatial distribution of water loss in the basin and its surroundings. Excluding the seasonal signals, between January 2021 and August 2022, the GNSS stations underwent uplift, up to 7 mm, which corresponds to ∼70 Gtons of water loss. Compared to Global Land Data Assimilation System and Gravity Recovery and Climate Experiment estimates, GNSS results show a similar temporal evolution of water content but a more heterogeneous distribution of values. We show that continuous GNSS networks provide an effective way to monitor multiannual trend changes in water storage even in small water basins and serve as a reliable indicator of drought severity.

中文翻译：

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根据 GNSS 测量得出的波河流域（意大利北部）干旱引起的垂直位移和水损失

我们研究全球导航卫星系统（GNSS）站的垂直地面位移时间序列，以测量与波河流域水文干旱相关的变形。着眼于年际趋势变化，而不是季节性（年度）成分，我们发现了一个明显的空间相关变形信号，该信号与波河水位和 SPEI-12 干旱指数的变化在时间上（反）相关，并且站点在周期内向上移动河流/指数水位下降，反之亦然。在 2021 年至 2022 年期间，我们估计了流域及其周边地区的水流失量和空间分布，最终导致了过去两个世纪以来最严重的干旱。排除季节性信号，2021 年 1 月至 2022 年 8 月期间，GNSS 站发生了高达 7 毫米的抬升，相当于约 70 吨的水损失。与全球陆地数据同化系统以及重力恢复和气候实验估计相比，GNSS 结果显示出相似的含水量时间演变，但值的分布更加异质。我们表明，连续的 GNSS 网络提供了一种有效的方法来监测水储存的多年趋势变化，即使在小型水盆地也是如此，并作为干旱严重程度的可靠指标。