Effects of Water-Table Configuration on the Planetary Boundary Layer over the San Joaquin River Watershed, California

Abstract

The boundary layer, land surface, and subsurface are important coevolving components of hydrologic systems. While previous studies have examined the connections between soil moisture, groundwater, and the atmosphere, the atmospheric response to regional water-table drawdown has received less attention. To address this question, a coupled hydrologic–atmospheric model [Parallel Flow hydrologic model (ParFlow) and WRF] was used to simulate the San Joaquin River watershed of central California. This study focuses specifically on the planetary boundary layer (PBL) in simulations with two imposed water-table configurations: a high water table mimicking natural conditions and a lowered water table reflecting historic groundwater extraction in California’s Central Valley, although effect of irrigation was not simulated. An ensemble of simulations including three boundary layer schemes and six initial conditions was performed for both water-table conditions to assess conceptual and initial condition uncertainty. Results show that increased regional water-table depth is associated with a significant increase in peak PBL height for both initial condition and boundary layer scheme conditions, although the choice of scheme interacts to affect the magnitude of peak PBL height change. Analysis of simulated land surface fluxes shows the change in PBL height can be attributed to decreasing midday evaporative fraction under lowered water-table conditions. Furthermore, the sensitivity of PBL height to changes in water-table depth appears to depend on local water-table variation within 10 m of the land surface and the regional average water-table depth. Finally, soil moisture changes associated with lowered water tables are linked to changes in PBL circulation as indicated by vertical winds and turbulence kinetic energy.

Importance of river water recharge to the San Joaquin Valley groundwater system

“…Recharge in premodern floodplains was likely slower than recharge on cultivated fields, allowing water to reach thermal equilibrium with the surroundings at temperatures closer to the mean annual air temperature. The extensive irrigation with river water also impacts air temperatures through the irrigation cooling effect (Kueppers, Snyder, & Sloan, ), the height of the planetary boundary layer (Gilbert, Maxwell, & Gochis, ), and precipitation patterns (Yang et al, ).…”

“…A large range of noble gas recharge temperatures (σ = 3.1°C) is with river water also impacts air temperatures through the irrigation cooling effect (Kueppers, Snyder, & Sloan, 2007), the height of the planetary boundary layer (Gilbert, Maxwell, & Gochis, 2017), and precipitation patterns (Yang et al, 2017). Fossil (Pleistocene) groundwater has mostly recharged as local precipitation because flow paths from the foothills to the discharge areas near the valley centre are naturally longer (Izbicki, Radyk, & Michel, 2000 Local precipitation comprises 55 ± 4% of modern groundwater in the San Joaquin Valley.…”

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, ).…”

Quantifying the Impact of Subsurface‐Land Surface Physical Processes on the Predictive Skill of Subseasonal Mesoscale Atmospheric Simulations

“…Compared to atmospheric models routinely used for weather prediction, these models have a more detailed representation of subsurface-land surface physical processes with an explicit consideration of groundwater-surface water interactions. A growing body of literature emphasizes their potential for improving our understanding of the connections between groundwater and atmospheric processes (Gilbert et al, 2017;Keune et al, 2016Keune et al, , 2018Rahman et al, 2015). To date, only very few studies assessed the impact of such improved subsurface physics on the skills of atmospheric predictions (e.g., Larsen, Christensen, et al, 2016a;Larsen, Rasmussen et al, 2016b).…”