Groundwater is a crucial resource to support surface water bodies via groundwater discharge. In this study, we applied two methods of estimating global environmentally critical groundwater discharge, defined as the flux of groundwater to streamflow necessary to maintain a healthy environment, from 1960 to 2010: the Presumptive Standard stipulates that a standard proportion of groundwater discharge should be maintained at all timesteps, while the Q* is a low-flow index that focuses on critical periods. We calculated these critical flow thresholds using simulated natural groundwater discharge, and estimated violations of the thresholds when human-impacted groundwater discharge dropped too low. Our global assessment of the frequency and severity of violations over all timesteps in our study period showed that the Presumptive Standard estimated more frequent and severe violations than the Q*, but that the spatial patterns were similar for both methods. During low-flow periods, when the relative importance of groundwater to support streamflow is greatest, both methods estimated similar magnitudes of violation frequency and severity. We further compared our results to a method of estimating environmentally critical streamflow, Variable Monthly Flow, which does not explicitly consider groundwater. From the differences in violation frequency between these groundwater-centric and surface water-centric methods, we evaluated the influence of including groundwater contributions to streamflow in environmental flow assessments. Our results show that including groundwater in such assessments is particularly important for regions with high groundwater demands in the drier climates of the world, while it is less important for regions with low groundwater demands and more humid climates.

中文翻译：

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比较全球违反环境关键型地下水排放阈值的情况


地下水是通过地下水排放来支持地表水体的重要资源。在这项研究中，我们应用了两种方法来估计 1960 年至 2010 年全球环境关键型地下水排放量，定义为维持健康环境所需的地下水流通量：推定标准规定在所有时间步长都应保持地下水排放的标准比例，而 Q* 是侧重于关键时期的低流量指数。我们使用模拟的自然地下水排放计算了这些临界流量阈值，并估计了当人为影响的地下水排放下降过低时超出阈值的阈值。我们对研究期间所有时间步长中违规频率和严重程度的全局评估表明，推定标准估计的违规比 Q* 更频繁和更严重，但两种方法的空间模式相似。在低流量时期，当地下水对支持径流的相对重要性最大时，两种方法估计的违规频率和严重程度相似。我们进一步将我们的结果与一种估计环境关键型径流的方法 Variable Monthly Flow 进行了比较，该方法没有明确考虑地下水。根据这些以地下水和以地表水为中心的方法之间的违规频率差异，我们评估了在环境流量评估中包括地下水对径流的贡献的影响。我们的结果表明，在世界气候较干燥的情况下，将地下水纳入此类评估对于地下水需求量大的地区尤为重要，而对于地下水需求量低和气候较潮湿的地区，地下水需求量较小。