Over the past century, groundwater levels in California's San Joaquin Valley have dropped by more than 30 m in some areas mostly due to excessive groundwater extraction used to irrigate agricultural lands and sustain a growing population. Between 2012 and 2015, California experienced the worst drought in its recorded history, depleting surface water supplies and further exacerbating groundwater depletion in the region. Due to a lack of groundwater regulation, exact quantities of extracted groundwater in California are unknown and hard to quantify. Recent adoption of the Sustainable Groundwater Management Act has intensified efforts to identify sustainable groundwater use. However, understanding sustainable use in a highly productive agricultural system with an extremely complex surface water allocation system, variable groundwater use, and spatially extensive and diverse irrigation practices is no easy task. Using an integrated hydrologic model coupled with a land surface model, we evaluated how water management activities, specifically a suite of irrigation and groundwater pumping scenarios, impact surface water–groundwater fluxes and storage components and how those activities and the relationships between them change during drought. Results showed that groundwater pumping volume had the most significant impact on long‐term water storage changes. A comparison with total water storage anomaly (TWSA) estimates from NASA's Gravity Recover and Climate Experiment (GRACE) provided some insight regarding which combinations of pumping and irrigation matched the GRACE TWSA estimates, lending credibility to these scenarios. In addition, the majority of long‐term water storage changes during the recent drought occurred in groundwater storage in the deeper subsurface.

中文翻译：

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集成水文模型，以解决干旱期间水管理的影响

在过去的一个世纪中，加利福尼亚州圣华金河谷的地下水位在某些地区下降了30 m以上，这主要是由于用于灌溉农田和维持人口增长的过量开采地下水所致。在2012年至2015年之间，加利福尼亚州经历了有记录以来最严重的干旱，耗尽了地表水供应，并进一步加剧了该地区的地下水枯竭。由于缺乏地下水管理，加利福尼亚的提取地下水的确切数量未知，并且难以量化。最近通过的《可持续地下水管理法》加大了努力，以查明可持续的地下水用途。但是，要了解具有高度复杂的地表水分配系统的高产农业系统中的可持续利用，可变的地下水利用，在空间上广泛多样的灌溉实践绝非易事。通过使用综合水文模型和土地表面模型，我们评估了水管理活动（特别是一系列灌溉和地下水抽取方案）如何影响地表水-地下水通量和存储成分，以及干旱期间这些活动及其之间的关系如何变化。结果表明，地下水的抽水量对长期储水量的变化影响最大。与美国宇航局重力恢复和气候实验（GRACE）的总储水异常（TWSA）估计值的比较提供了一些见识，涉及哪些抽水和灌溉组合与GRACE TWSA估计值相匹配，从而为这些情况提供了可信度。此外，