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Title: Upscaling key ecosystem functions across the conterminous United States by a waterâcentric ecosystem model
Author: Sun, Ge; Caldwell, Peter; Noormets, Asko; McNulty, Steven G.; Cohen, Erika; et., al.
Source: Journal of Geophysical Research 116:G00J05
Description: We developed a waterâcentric monthly scale simulation model (WaSSIâC) by integrating empirical water and carbon flux measurements from the FLUXNET network and an existing water supply and demand accounting model (WaSSI). The WaSSIâC model was evaluated with basinâscale evapotranspiration (ET), gross ecosystem productivity (GEP), and net ecosystem exchange (NEE) estimates by multiple independent methods across 2103 eightâdigit Hydrologic Unit Code watersheds in the conterminous United States from 2001 to 2006. Our results indicate that WaSSIâC captured the spatial and temporal variability and the effects of large droughts on key ecosystem fluxes. Our modeled mean (Â±standard deviation in space) ET (556 Â± 228 mm yrâ1) compared well to Moderate Resolution Imaging Spectroradiometer (MODIS) based (527 Â± 251 mm yrâ1) and watershed water balance based ET (571 Â± 242 mm yrâ1). Our mean annual GEP estimates (1362 Â± 688 g C mâ2 yrâ1) compared well (R2 = 0.83) to estimates (1194 Â± 649 g C mâ2 yrâ1) by eddy fluxâbased ECâMOD model, but both methods led significantly higher (25â30%) values than the standard MODIS product (904 Â± 467 g C mâ2 yrâ1). Among the 18 water resource regions, the southeast ranked the highest in terms of its water yield and carbon sequestration capacity. When all ecosystems were considered, the mean NEE (â353 Â± 298 g C mâ2 yrâ1) predicted by this study was 60% higher than ECâMODâs estimate (â220 Â± 225 g C mâ2 yrâ1) in absolute magnitude, suggesting overall high uncertainty in quantifying NEE at a large scale. Our waterâcentric model offers a new tool for examining the tradeâoffs between regional water and carbon resources under a changing environment.
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Sun, Ge; Caldwell, Peter; Noormets, Asko; McNulty, Steven G.; Cohen, Erika; et. al. 2011. Upscaling key ecosystem functions across the conterminous United States by a waterâcentric ecosystem model. Journal of Geophysical Research 116:G00J05.
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