Groundwater and surface water scaling over the continental US using a hyperresolution, integrated hydrologic model.

Abstract:

Groundwater is an important component of the hydrologic cycle yet its importance is often overlooked. Aquifers are a critical water resource, particularly in irrigation, but also participates in moderating the land-energy balance over the so-called critical zone of 2-10m in water table depth. Yet, the scaling behavior of groundwater is not well known. Here we present the results of a parallel, integrated hydrologic model simulating surface and subsurface flow and conservative transport at high spatial resolution (1km) over much of continental North America (~6,300,000 or 6.3M km²), which is considered a grand challenge in hydrology. In addition to simulating coupled groundwater, surface-water and unsaturated flow, we incorporate a Lagrangian transport component that provides an estimate of both mean travel time and distribution of water recharged at the ground surface over North America, an open question in hydrology. Results show power-law scaling of flow and water table depth and a complex, non-Gaussian residence time distribution indicating that temporal scaling of flow paths observed in small catchments (1-3.5 km²) may persist to continental scales (6.3M km²). These results provide mechanistic insight into several important questions in earth science such as the paradox of old carbon in streams or hydrologic controls on chemical weathering and land formation. Furthermore, results are used to understand the scaling behavior of groundwater over the continent at high resolution. Implications for understanding dominant hydrological processes at large scales will be discussed.