Global‐scale gradient‐based groundwater models are a new endeavor for hydrologists who wish to improve global hydrological models (GHMs). In particular, the integration of such groundwater models into GHMs improves the simulation of water flows between surface water and groundwater and of capillary rise and thus evapotranspiration. Currently, these models are not able to simulate water table depth adequately over the entire globe. Unsatisfactory model performance compared to well observations suggests that a higher spatial resolution is required to better represent the high spatial variability of land surface and groundwater elevations. In this study, we use New Zealand as a testbed and analyze the impacts of spatial resolution on the results of global groundwater models. Steady‐state hydraulic heads simulated by two versions of the global groundwater model G³M, at spatial resolutions of 5 arc‐minutes (9 km) and 30 arc‐seconds (900 m), are compared with observations from the Canterbury region. The output of three other groundwater models with different spatial resolutions is analyzed as well. Considering the spatial distribution of residuals, general patterns of unsatisfactory model performance remain at the higher resolutions, suggesting that an increase in model resolution alone does not fix problems such as the systematic overestimation of hydraulic head. We conclude that (1) a new understanding of how low‐resolution global groundwater models can be evaluated is required, and (2) merely increasing the spatial resolution of global‐scale groundwater models will not improve the simulation of the global freshwater system.

中文翻译：

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空间分辨率在全球地下水建模中的重要性

对于希望改进全球水文模型（GHM）的水文学家来说，基于全球规模的梯度地下水模型是一项新的尝试。特别是，将这些地下水模型集成到GHM中可以改善对地表水和地下水之间的水流以及毛细上升和蒸散的模拟。目前，这些模型无法在整个地球上充分模拟地下水位。与油井观测结果相比，模型性能欠佳，这表明需要更高的空间分辨率才能更好地表现出地表和地下水高程的高空间变异性。在这项研究中，我们将新西兰用作测试平台，并分析空间分辨率对全球地下水模型结果的影响。^将3 M，5弧分（9 km）和30弧秒（900 m）的空间分辨率与坎特伯雷地区的观测结果进行了比较。还分析了其他三种具有不同空间分辨率的地下水模型的输出。考虑到残差的空间分布，模型性能不理想的一般模式仍保持较高的分辨率，这表明仅模型分辨率的提高并不能解决诸如液压头的系统过高估计之类的问题。我们得出的结论是：（1）需要对如何评估低分辨率的全球地下水模型有新的认识，（2）仅增加全球规模的地下水模型的空间分辨率并不能改善全球淡水系统的模拟。