Declines in terrestrial water storage (TWS) exacerbate regional water scarcity and global sea level rise. Increasing evidence has shown that recent TWS declines are substantial in ecologically fragile drylands, but the mechanism remains unclear. Here, by synergizing satellite observations and model simulations, we quantitatively attribute TWS trends during 2002–2016 in major climate zones to three mechanistic drivers: climate variability, climate change, and direct human activities. We reveal that climate variability had transitory and limited impacts (<20%), whereas warming-induced glacier loss and direct human activities dominate the TWS loss in humid regions (∼103%) and drylands (∼64%), respectively. In non-glacierized humid areas, climate variability generated regional water gains that offset synchronous TWS declines. Yet in drylands, TWS losses are enduring and more widespread with direct human activities, particularly unsustainable groundwater abstraction. Our findings highlight the substantive human footprints on the already vulnerable arid regions and an imperative need for improved dryland water conservation.

中文翻译：

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全球旱地和潮湿地区陆地储水量下降的不同原因

陆地储水量 (TWS) 的减少加剧了区域水资源短缺和全球海平面上升。越来越多的证据表明，生态脆弱的旱地最近的 TWS 下降幅度很大，但机制仍不清楚。在这里，通过协同卫星观测和模型模拟，我们将 2002-2016 年主要气候区的 TWS 趋势定量归因于三个机制驱动因素：气候变率、气候变化和直接的人类活动。我们发现气候变异具有短暂和有限的影响（<20%），而变暖引起的冰川损失和直接的人类活动分别主导了潮湿地区（~103%）和旱地（~64%）的 TWS 损失。在非冰川湿润地区，气候变化产生的区域增水抵消了同步的 TWS 下降。然而在旱地，TWS 损失在人类直接活动中持续存在且更为普遍，尤其是不可持续的地下水抽取。我们的研究结果突出了已经脆弱的干旱地区的大量人类足迹，以及改善旱地水资源保护的迫切需要。