Abstract
Abstract. Effects of hydraulic redistribution (HR) on hydrological, biogeochemical, and ecological processes have been demonstrated in the field, but the current generation of standard earth system models does not include a representation of HR. Though recent studies have examined the effect of incorporating HR into land surface models, few (if any) have done cross-site comparisons for contrasting climate regimes and multiple vegetation types via the integration of measurement and modeling. Here, we incorporated the HR scheme of Ryel et al. (2002) into the NCAR Community Land Model Version 4.5 (CLM4.5), and examined the ability of the resulting hybrid model to capture the magnitude of HR flux and/or soil moisture dynamics from which HR can be directly inferred, to assess the impact of HR on land surface water and energy budgets, and to explore how the impact may depend on climate regimes and vegetation conditions. Eight AmeriFlux sites with contrasting climate regimes and multiple vegetation types were studied, including the Wind River Crane site in Washington State, the Santa Rita Mesquite savanna site in southern Arizona, and six sites along the Southern California Climate Gradient. HR flux, evapotranspiration (ET), and soil moisture were properly simulated in the present study, even in the face of various uncertainties. Our cross-ecosystem comparison showed that the timing, magnitude, and direction (upward or downward) of HR vary across ecosystems, and incorporation of HR into CLM4.5 improved the model-measurement matches of evapotranspiration, Bowen ratio, and soil moisture particularly during dry seasons. Our results also reveal that HR has important hydrological impact in ecosystems that have a pronounced dry season but are not overall so dry that sparse vegetation and very low soil moisture limit HR.
Highlights
Hydraulic redistribution (HR) is the transport of water from wetter to drier soils through plant roots (Burgess et al, 1998)
The cross-ecosystem comparisons demonstrate that the timing, magnitude, and direction of HR vary across ecosystems (Figs. 1, 5), and incorporation of HR into CLM4.5 improved model-measurement match during dry seasons (Table 5)
The hydrological impact of HR is substantial in ecosystems that have a pronounced dry season but are not overall so dry that sparse vegetation and very low soil moisture limit HR (Figs. 5, 7, 8)
Summary
Hydraulic redistribution (HR) is the transport of water from wetter to drier soils through plant roots (Burgess et al, 1998). C. Fu et al.: Combined measurement and modeling of the hydrological impact of hydraulic redistribution al., 2013), and ecological (e.g., Hawkins et al, 2009) processes have been amply demonstrated in the field, the current generation of standard dynamic global vegetation and earth system models do not include a representation of HR (Neumann and Cardon, 2012; Warren et al, 2015). Few (if any) has investigated the effects of HR on land surface water and energy cycles in a comprehensive manner by using both the monitoring and modeling methods for contrasting climate regimes and multiple vegetation types. We attempt to address this research gap based on both field measurements and numerical modeling at an ecologically broad selection of eight AmeriFlux sites characterized by contrasting climate regimes and multiple vegetation types. The other six are new sites along the Southern California Climate Gradient (US-SCs, g, f, w, c, and d), each with a pronounced dry season, where we suspect HR may occur during dry periods
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