Simulating groundwater uptake and hydraulic redistribution by phreatophytes in a high-resolution, coupled subsurface-land surface model

Highlights

• Belowground processes in Earth system models continue to present challenges.
• ParFlow.CLM modified to include more realistic root water uptake functions.
• New model capable of predicting groundwater uptake, hydraulic redistribution.
• Model compares favorably to eight years of data from AmeriFlux site in California.
• Improved prediction of latent heat fluxes in drylands with phreatophytes.

Abstract

Several new functions representing groundwater dependent vegetation were incorporated into a coupled subsurface-land surface model, ParFlow.CLM, in order to adequately describe groundwater water uptake, hydraulic redistribution, and plant water stress. The modified model was used to conduct three-dimensional, stand-scale simulations of a Mediterranean oak savanna in California. It performed well and captured daily, hourly and spatial water and energy dynamics, as well as groundwater evapotranspiration rates. The new model was then compared to various approaches, the original ParFlow.CLM and a version using a root water uptake compensation equation. During the dry season, the modified model closely predicted the measured transpiration rate while the original model predicted that it would become zero and the compensation approach overestimated it by nearly double. The modified model also allowed for analysis of several key ecohydrological processes, namely the hydraulic redistribution when plants were both active and dormant, the leaf water potential, and xylem cavitation.