The Pleistocene-Holocene climate transition resulted in a dramatic reduction in groundwater recharge in many aquifers in arid and semiarid regions throughout the world. This study conducted numerical experiments to compare the evolution of groundwater hydraulics and age patterns in arid and semiarid aquifers in response to transient conditions associated with recharge decline from the Pleistocene to the Holocene. Our results show that after a rapid reduction in recharge, the amplitude of water-table undulations and regional groundwater slope both reduced. This resulted in a general, and relatively rapid, contraction of local flow systems and an increase in the extent of intermediate and regional systems. The previous hierarchy of local, intermediate, and regional flow systems was completely replaced by largely horizontal and regional flow patterns after ~10,000 yr. However, in stark contrast, we observed that the original Pleistocene age patterns have remained almost unchanged throughout the 10,000 yr Holocene period. Thus, groundwater age is more likely to be indicative of past rather than current flow systems. Consequently, due to this age persistence, the use of modern groundwater age data to calibrate models or compute recharge with methods that do not account for this potentially significant spatial and temporal mismatch between age and hydraulics will be misleading and erroneous. This has significant implications for hydrogeologic analyses. The findings of this study may also apply to areas that have undergone dramatic changes in land cover or land use that strongly influence transient groundwater recharge processes.

中文翻译：

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古水文地质时间尺度上地形驱动的地下水流中的地下水年龄持久性

更新世-全新世气候转变导致全球干旱和半干旱地区许多含水层的地下水补给量急剧减少。这项研究进行了数值实验，以比较干旱和半干旱含水层中地下水水力学和年龄模式的演变，以响应与从更新世到全新世的补给减少相关的瞬态条件。我们的研究结果表明，在补给量快速减少后，地下水位波动幅度和区域地下水坡度均减小。这导致局部流动系统普遍且相对迅速地收缩，中间和区域系统的范围扩大。以前的层次结构是本地的、中间的、大约 10,000 年后，区域流动系统完全被水平和区域流动模式所取代。然而，与此形成鲜明对比的是，我们观察到原始的更新世年龄模式在整个 10,000 年全新世时期几乎保持不变。因此，地下水年龄更有可能表明过去而不是当前的流动系统。因此，由于这种年龄的持续性，使用现代地下水年龄数据来校准模型或计算补给量的方法不考虑年龄和水力之间这种潜在的显着空间和时间不匹配将是误导和错误的。这对水文地质分析具有重要意义。