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.

Indian river basins are intensively managed with country-specific agricultural practices of cultivating submerged paddy and uncontrolled groundwater (GW) irrigation. Numerical experiments with the state-of-the-art land surface models, such as variable infiltration capacity (VIC), without incorporating region-specific practices, could be misleading. Here, we coupled VIC with 2D GW model AMBHAS, incorporating India-specific irrigation practices and crop practices, including submerged paddy fields. We performed numerical experiments to understand the causal factors of GW depletion in the northwest Indo-Gangetic plain (IGP). We identify widespread flood irrigation and cultivation of water-intensive paddy as critical drivers of the declining GW scenario. Our numerical experiments suggest that the introduction of drip irrigation reduces GW depletion in the northwest, but does not change the sign of GW level trends. The GW levels in the non-paddy fields of the middle IGP are less sensitive to irrigation practices due to the high return flow to GW for flood irrigation.

The effects of anthropogenic water use play a significant role in determining the hydrological cycle of north India. This paper explores anthropogenic impacts within the region's hydrological regime by explicitly including observed human water use behaviour, irrigation infrastructure and the natural environment in the CHANSE (Coupled Human And Natural Systems Environment) socio‐hydrological modelling framework. The model is constrained by observed qualitative and quantitative information collected in the study area, along with climate and socio‐economic variables from additional sources. Four separate scenarios, including business as usual (BAU, representing observed irrigation practices), groundwater irrigation only (where the influence of the canal network is removed), canal irrigation only (where all irrigation water is supplied by diverted surface water) and rainfed only (where all human interventions are removed) are used. Under BAU conditions the modelling framework closely matched observed groundwater levels. Following the removal of the canal network, which forces farmers to rely completely on groundwater for irrigation, water levels decrease, while under a canal‐only scenario flooding occurs. Under the rainfed‐only scenario, groundwater levels similar to current business‐as‐usual conditions are observed, despite much larger volumes of recharge and discharge entering and leaving the system under BAU practices. While groundwater abstraction alone may lead to aquifer depletion, the conjunctive use of surface and groundwater resources, which includes unintended contributions of canal leakage, create conditions similar to those where no human interventions are present. Here, the importance of suitable water management practices, in maintaining sustainable water resources, is shown. This may include augmenting groundwater resources through managed aquifer recharge and reducing the impacts on aquifer resources through occasional canal water use where possible. The importance of optimal water management practices that highlight trade‐offs between environmental impact and human wellbeing are shown, providing useful information for policy makers, water managers and users. © 2019 John Wiley & Sons, Ltd.

Like other countries, the UK has opted for deep geological disposal for the long-term, safe management of higher activity radioactive waste. However, a site and a geological environment have yet to be identified to host a geological disposal facility. In considering its long-term safety functionality, it is necessary to consider natural processes, such as permafrost development, that have the potential to alter the geological environment over the time-scale of glacial-interglacial cycles. We applied a numerical model to simulate the impact of long-term climatic variability on groundwater flow and permafrost dynamics in two contrasting geological settings in Great Britain: (i) higher strength rocks (HSR) overlain by higher permeability sandstones with a high topographic gradient (GS1); (ii) a mixed sedimentary sequence of high and low permeability rocks resting on igneous HSR with a very low topographic gradient (GS2). We evaluated the sensitivity of simulated permafrost thickness to a variety of climatic and subsurface conditions. Uncertainty in the scaling of the surface temperature time-series, 10-25 degrees C below present day temperature, has the largest impact on maximum permafrost thickness, PFmax, compared to other variables. However, considering plausible parameter ranges for UK settings, PFmax is up to twice as sensitive to changes in thermal conductivity and geothermal heat flux than to changes in porosity. Heat advection only affects modelled PFmax for high hydraulic conductivity rocks and if permafrost is considered to be relatively permeable. Whilst local differences in permafrost thickness of Lens of meters, caused by variations in heat advection, are of minor importance over glacial-interglacial cycles, heal advection can be important in the development of taliks and the maintenance of a more active groundwater flow system. We conclude that it is likely to be important to simulate the effect of heat advection on coupled permafrost and groundwater flow systems in settings containing higher permeability lithological sequences. (C) 2019 British Geological Survey (C) UKRI 2018. Published by Elsevier B.V.