Bradford and othersEcohydrologyin adjacent sagebrush lodgepole-pine ecosystems
Appendix 4. Validation of LodgepolePineRepresentation in SOILWAT
SOILWAT, a daily time step soil water simulation model, was developed and tested in the semiarid western US shortgrass steppe (Parton 1978; Sala and others 1992) and previously used and validated (Appendix 3) in shrublands(Bradford and Lauenroth 2006; Schlaepfer and others 2012; Schlaepfer and others In Press).
We compared SOILWAT output with volumetric water content (VWC) and evapotranspiration (ET) measurements taken at Chimney Park, Wyoming during 2009 and 2010. For these comparisons, soil layers in SOILWAT were parameterized with field-measured soil texture and defined to correspond with the three depths at which VWC was measured. Daily weather data from Chimney Park was used directly in SOILWAT (Figure A4.1). VWC was measured at each depth using Campbell Scientific CS616 sensors. ET was measured at Chimney Park using eddy covariance.
SOILWAT output and measured VWC were similar in magnitude and seasonality, especially in the surface (0-15 cm) and intermediate (15-45 cm). In addition, the seasonal patterns of increasing soil water in the spring, general decrease by midsummer and dry winter soils are reflected in both the observations and model output. Because SOILWAT runs on a daily time step and does not simulate soil water content greater than field capacity, it does not capture the brief spikes in VWC present in the observations during spring 2010. SOILWAT estimates of ET are consistent with the eddy covariance estimates (Figure A4.2).
Because snow dynamics can have important influence over many components of ecosystem water balance in temperate coniferous forests (Knight and others 1985; Balesand others 2006; Molotchand others 2009), we contrasted SOILWAT estimates of snowpack accumulation and melt with field measurements from the Lightning Ridge Soil Climate Analysis Network (SCAN) site. The Lightning Ridge site is located in Northern Utah (41° 22’ N, 111° 29’ W)at 2500 m elevation in a mixed conifer forest. Although Lightning Ridge is slightly higher than our ecotone sites, and the vegetation is correspondingly different, the multi-year record of snowpack dynamics facilitates a useful comparison with SOILWAT snowpack estimates. Although SOILWAT slightly under-estimates maximum snow water equivalent (SWE), the timing of snowpack initiation and melt-off are consistent these field-measured estimates.
Eddy covariance and soil moisture data presented below were generously provided by Elise Pendall and Brent Ewers, processed by David Reed (all University of Wyoming), with funding support from McIntire-Stennis, Wyoming Water Development Commission, U.S. Geological Survey and National Science Foundation through Emerging Topics in Biogeochemical Cycles.
Figure A4.1: Comparison of observed (red lines) and modeled (black lines) volumetric soil water content for a lodgepole pine forest in Chimney Park, WY at three soil depths. Also shown is precipitation (blue bars in top panel), water infiltration into the soil (light blue bars in middle panel), and snow water equivalent (SWE; purple area in bottom panel).
Figure A4.2: Comparison of observed (red dots) and modeled (black line) evapotranspiration for a lodgepole pine forest at Chimney Park, Wyoming.
Bradford and othersEcohydrologyin adjacent sagebrush lodgepole-pine ecosystems
Figure A4.3: Comparison of observed (blue line) and modeled (purple area) snow water equivalent (SWE) in the snowpack at the Lightning Ridge Soil Climate Analysis Network (SCAN) site in northern Utah.
Bradford and othersEcohydrologyin adjacent sagebrush lodgepole-pine ecosystems
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Knight, D.H., Fahey, T.J. & Running, S.W. (1985) Water and nutrient outflow from contrasting lodgepole pine forests in Wyoming Ecological Monographs,55, 29-48.
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