One of the first and most important decisions facing practitioners when constructing a numerical groundwater model is vertical discretization. Several factors will influence this decision, such as the conceptual model of the system and hydrostratigraphy, data availability, resulting computational burden, and the purpose of the modeling analysis. Using a coarse vertical discretization is an attractive option for practitioners because it reduces data requirements and model construction efforts, can increase model stability, and can reduce computational demand. However, using a coarse vertical discretization as a form of model simplification is not without consequence; this may give rise to unwanted side‐effects such as biases in decision‐relevant simulated outputs. Given its foundational role in the modeled representation of the aquifer system, herein we investigate how vertical discretization may affect decision‐relevant simulated outputs using a paired complex‐simple model analysis. A Bayesian framework and decision analysis approach are adopted. Two case studies are considered, one of a synthetic, linked unsaturated‐zone/surface‐water/groundwater hydrologic model and one of a real‐world linked surface‐water/groundwater hydrologic‐nitrate transport model. With these models, we analyze decisions related to abstraction‐induced changes in ecologically important streamflow characteristics and differences in groundwater and surface‐water nitrate concentrations and mass loads following potential land‐use change. We show that for some decision‐relevant simulated outputs, coarse vertical discretization induces bias in important simulated outputs, and can lead to incorrect resource management action. For others, a coarse vertical discretization has little or no consequence for resource management decision‐making.

中文翻译：

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基于风险的决策中地下水模型垂直离散化的后果

垂直离散化是构建数值地下水模型时从业人员面临的第一个也是最重要的决定之一。几个因素将影响该决策，例如系统和水文地层的概念模型，数据可用性，由此产生的计算负担以及建模分析的目的。使用粗略的垂直离散化对于从业者来说是一个有吸引力的选择，因为它减少了数据需求和模型构建工作，可以增加模型稳定性，并可以减少计算需求。但是，使用粗略的垂直离散化作为模型简化的形式并非没有后果；这可能会引起不良的副作用，例如与决策相关的模拟输出中的偏差。鉴于其在含水层系统模型表示中的基础性作用，在本文中，我们使用配对的复杂模型分析来研究垂直离散化如何影响与决策相关的模拟输出。采用贝叶斯框架和决策分析方法。考虑了两个案例研究，一个是合成的，链接的非饱和区/地表水/地下水水文模型，另一个是现实世界的链接的地表水/地下水水文硝酸盐运移模型。利用这些模型，我们分析了与潜在生态用途变化引起的重要生态流量特征的抽象变化以及地下水和地表水硝酸盐浓度及质量负荷的差异有关的决策。我们表明，对于某些与决策相关的模拟输出，粗略的垂直离散化会在重要的模拟输出中引起偏差，并可能导致错误的资源管理操作。对于其他人，粗略的垂直离散化对资源管理决策几乎没有影响。