Studying the influence of groundwater representations on land surface‐atmosphere feedbacks during the European heat wave in 2003

Abstract

The impact of 3D groundwater dynamics as part of the hydrologic cycle is rarely considered in regional climate simulation experiments. However, there exists a spatial and temporal connection between groundwater and soil moisture near the land surface, which can influence the land surface‐atmosphere feedbacks during heat waves. This study assesses the sensitivity of bedrock‐to‐atmosphere simulations to groundwater representations at the continental scale during the European heat wave 2003 using an integrated fully coupled soil‐vegetation‐atmosphere model. The analysis is based on the comparison of two groundwater configurations: (1) 3D physics‐based variably saturated groundwater dynamics and (2) a 1D free drainage (FD) approach. Furthermore, two different subsurface hydrofacies distributions (HFD) account for the uncertainty of the subsurface hydraulic characteristics, and ensemble simulations address the uncertainty arising from different surface‐subsurface initial conditions. The results show that the groundwater representation significantly impacts land surface‐atmosphere processes. Differences between the two groundwater configurations follow subsurface patterns, and the largest differences are observed for shallow water table depths. While the physics‐based setup is less sensitive to the HFD, the parameterized FD simulations are highly sensitive to the hydraulic characteristics of the subsurface. An analysis of variance shows that both, the groundwater configuration and the HFD, induce variability across all compartments with decreasing impact from the subsurface to the atmosphere, while the initial condition has only a minor impact.

Impact of a shallow groundwater table on the global water cycle in the IPSL land–atmosphere coupled model

“…It is particularly important in the framework of future climate projections, as groundwater, because of its long residence time, could help alleviate the projected aridity increase over land (Berg et al 2016) and the strengthened heat extremes, as reported by Keune et al (2016) based on simulations of the European heat wave in 2003.…”

Why Do Large‐Scale Land Surface Models Produce a Low Ratio of Transpiration to Evapotranspiration?

“…Szilagyi et al () further confirmed the link between groundwater and ET in Nebraska through observational data. In turn, these impacts may propagate into the atmospheric boundary layer, affecting the planetary boundary layer height, air temperature, convective available potential energy, and convection precipitation (e.g., Gilbert et al, ; Keune et al, ; Maxwell et al, ; Rahman et al, ; Rihani et al, ). A growing body of literature also suggests that lateral subsurface flow can substantially enhance the T / ET ratio (Fang et al, ; Maxwell & Condon, ), and this effect becomes slightly more significant for higher model resolutions (Shrestha et al, ).…”

Coupling a three-dimensional subsurface flow and transport model with a land surface model to simulate stream–aquifer–land interactions (CP v1.0)

“…Compared to simulations of regional climate models coupled to traditional LSMs, such a physically based approach shows less sensitivity to uncertainty in the subsurface hydraulic characteristics that could propagate from deep subsurface to free troposphere (Keune et al, 2016), while other physical representations (e.g., parameterizations in evaporation and transpiration, atmospheric boundary layer schemes) could have significant effects on the simulations as well . Therefore, it is of great scientific interest to further develop the integrated models and benchmarks to achieve improved understanding of complex interactions in the fully coupled Earth system.…”