Abstract
Better representations of groundwater processes need to be incorporated into large-scale hydrological models to improve simulations of regional- to global-scale hydrology and climate, as well as understanding of feedbacks between the human and natural systems. We incorporated a 2D groundwater flow model into the variable infiltration capacity (VIC) hydrological model code to address its lack of a lateral groundwater flow component. The water table was coupled with the variably saturated VIC soil column allowing bi-directional exchange of water between the aquifer and the soil. We then investigated how variations in aquifer properties and grid resolution affect modelled evapotranspiration (ET), runoff and groundwater recharge. We simulated nine idealised, homogenous aquifers with different combinations of transmissivity, storage coefficient, and three grid resolutions. The magnitude of cell ET, runoff, and recharge significantly depends on water table depth. In turn, the distribution of water table depths varied significantly as grid resolution increased from 1° to 0.05° for the medium and high transmissivity systems, resulting in changes of model-average fluxes of up to 12.3% of mean rainfall. For the low transmissivity aquifer, increasing the grid resolution has a minimal effect as lateral groundwater flow is low, and the VIC grid cells behave as vertical columns. The inclusion of the 2D groundwater model in VIC will enable the future representation of irrigation from groundwater pumping, and the feedbacks between groundwater use and the hydrological cycle.
Highlights
Human water requirement is increasing at the global scale [1] and has significantly modified hydrological processes through irrigation, artificial dams and water diversions [2]
We extended the previous approaches by integrating a 2D groundwater model into the variable infiltration capacity (VIC) code, implementing soil moisture–groundwater table interaction according to Niu et al [12], and enabling direct river–aquifer interaction
In the low T system, increasing the grid resolution has minimal effect as lateral groundwater flow is low, and the VIC grid cells behave as vertical columns
Summary
Human water requirement is increasing at the global scale [1] and has significantly modified hydrological processes through irrigation, artificial dams and water diversions [2]. Human–water interactions can significantly change the terrestrial water cycle; for example, groundwater-fed irrigation can transform regions from areas of moisture limited to energy limited evapotranspiration (ET), influencing both water and energy budgets [1,2,3,4,5,6]. Feedbacks between the human and natural systems can be complex, such as in the Indo-Gangetic basin where a spatially complex pattern of both groundwater depletion and areas of water logging is observed. This has occurred because of groundwater pumping and complex and dynamic recharge processes influenced by groundwater use, river flows and canal engineering [10]. Relatively few models have included lateral groundwater flow, even though it has been recognised as a key missing process [6,8], acting across multiple spatial scales: in humid areas at the hill-slope scale to the basin scale, to larger scales in semi-arid or arid regions where discharge areas can be remote from recharge areas [3]
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