Groundwater is the world's largest accessible source of fresh water. It playsa vital role in satisfying basic needs for drinking water, agriculture andindustrial activities. During times of drought groundwater sustains baseflowto rivers and wetlands, thereby supporting ecosystems. Most global-scalehydrological models (GHMs) do not include a groundwater flow component,mainly due to lack of geohydrological data at the global scale. For thesimulation of lateral flow and groundwater head dynamics, a realisticphysical representation of the groundwater system is needed, especially forGHMs that run at finer resolutions. In this study we present a global-scalegroundwater model (run at 6' resolution) using MODFLOW to construct anequilibrium water table at its natural state as the result of long-termclimatic forcing. The used aquifer schematization and properties are based onavailable global data sets of lithology and transmissivities combined with theestimated thickness of an upper, unconfined aquifer. This model is forcedwith outputs from the land-surface PCRaster Global Water Balance (PCR-GLOBWB) model, specifically netrecharge and surface water levels. A sensitivity analysis, in which the modelwas run with various parameter settings, showed that variation in saturatedconductivity has the largest impact on the groundwater levels simulated.Validation with observed groundwater heads showed that groundwater heads arereasonably well simulated for many regions of the world, especially forsediment basins (R2 = 0.95). The simulated regional-scalegroundwater patterns and flow paths demonstrate the relevance of lateralgroundwater flow in GHMs. Inter-basin groundwater flows can be a significantpart of a basin's water budget and help to sustain river baseflows,especially during droughts. Also, water availability of larger aquifersystems can be positively affected by additional recharge from inter-basingroundwater flows.
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机译：地下水是世界上最大的淡水资源。它在满足饮用水，农业和工业活动的基本需求方面起着至关重要的作用。在干旱时期，地下水维持着河流和湿地的基流，从而支持了生态系统。大多数全球尺度水文模型（GHM）不包括地下水流量分量，这主要是由于缺乏全球尺度的地文数据。为了模拟侧向流动和地下水位动态，需要对地下水系统进行真实的物理表示，尤其是对于以较高分辨率运行的GHM。在这项研究中，我们提出了一个全球规模的地下水模型（以6'分辨率运行），该模型使用MODFLOW来建立长期自然强迫作用下处于自然状态的平衡地下水位。所使用的含水层模式化和属性基于岩性和透射率的可用全局数据集，并结合上部无限制含水层的估计厚度。该模型由陆地表面PCRaster全球水平衡（PCR-GLOBWB）模型的输出（特别是净补给和地表水位）强制输出。对该模型进行了各种参数设置的敏感性分析表明，饱和电导率变化对模拟的地下水位影响最大。对观察到的地下水头进行的验证表明，在世界许多地区，特别是在沉积物中，地下水头得到了很好的模拟。盆地（ R 2 = 0.95）。模拟的区域尺度地下水模式和流径证明了GHM中横向地下水流的相关性。流域间的地下水流动可能是流域水预算的重要组成部分，有助于维持河流的基流，特别是在干旱期间。同样，较大的含水层系统的水利用率会受到基础间地下水流的额外补给的积极影响。
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