Upscaling key ecosystem functions across the conterminous United States by a water-centric ecosystem model

Abstract

[1] We developed a water-centric monthly scale simulation model (WaSSI-C) by integrating empirical water and carbon flux measurements from the FLUXNET network and an existing water supply and demand accounting model (WaSSI). The WaSSI-C model was evaluated with basin-scale evapotranspiration (ET), gross ecosystem productivity (GEP), and net ecosystem exchange (NEE) estimates by multiple independent methods across 2103 eight-digit Hydrologic Unit Code watersheds in the conterminous United States from 2001 to 2006. Our results indicate that WaSSI-C captured the spatial and temporal variability and the effects of large droughts on key ecosystem fluxes. Our modeled mean (±standard deviation in space) ET (556 ± 228 mm yr −1 ) compared well to Moderate Resolution Imaging Spectroradiometer (MODIS) based (527 ± 251 mm yr −1 ) and watershed water balance based ET (571 ± 242 mm yr −1 ). Our mean annual GEP estimates (1362 ± 688 g C m −2 yr −1 ) compared well (R 2 = 0.83) to estimates (1194 ± 649 g C m −2 yr −1 ) by eddy flux-based EC-MOD model, but both methods led significantly higher (25-30%) values than the standard MODIS product (904 ± 467 g C m −2 yr −1 ). 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 (−353 ± 298 g C m −2 yr −1 ) predicted by this study was 60% higher than EC-MOD's estimate (−220 ± 225 g C m −2 yr −1) in absolute magnitude, suggesting overall high uncertainty in quantifying NEE at a large scale. Our water-centric model offers a new tool for examining the trade-offs between regional water and carbon resources under a changing environment.

Regional effects of vegetation restoration on water yield across the Loess Plateau, China

“…Indeed, small watershed experiment studies worldwide (Zhang et al, 2001;Andreassian, 2004) and continental scale modelling studies suggest the hydrologic influences of vegetation restoration vary across a climatic gradient (Ma et al, 2008) and over the course of plant community establishment (Sun et al, 2006). However, few case studies (Sun et al, 2006(Sun et al, , 2011b are available to extend small-watershed study results to a large basin or a region although land management planning and policy decisions are made at those scales .…”

“…The MODIS-ET algorithm employs reanalysed surface meteorological data (0.05 • resolution) from the NASA Global Modelling and Assimilation Office with MODIS land cover, albedo, LAI and the Fraction of Absorbed Photosynthetically Active Radiation (FPAR) inputs for regional and global ET mapping and monitoring with 1 km resolution. The global ET model has been successfully evaluated using various flux datasets Sun et al, 2011b). Monthly LAI dynamic data are needed to drive the monthly ET model.…”

“…The 1-km resolution DEM from the US Geological Survey global HYDRO1K product was used to derive gridded climate data. Combining climatologic and topographic data, the point climate data were interpolated at a 1 km resolution with the thin-plate smoothing spline method provided by the ANUSPLIN 3.1 programme, (Wahba and Wendelberger, 1980;Hutchinson, 1991). The climate data interpolation method provides accurate estimates of spatial climatic variables by including the linear covariates rather than a constant lapse rate to represent the elevation effect on atmospheric pressure and temperature (Hutchinson, 1991) and also the method is able to provide a direct estimation of interpolation error and efficient diagnosis of data errors (Hutchinson and Gessler, 1994).…”

The tradeoff and synergy between ecosystem services in the Grain-for-Green areas in Northern Shaanxi, China

“…Uncertainty also exists in the estimation of ET for two reasons: (1) change in water storage may not have been negligible for certain wet years and (2) water resource use by communities and the impacts of soil conservation structures (e.g., check dams) were not involved. Overall, the method we adopted may introduce systematic errors at a level of approximately 15% (Sun et al, 2011b). …”

Forest Management Challenges for Sustaining Water Resources in the Anthropocene

“…For example, on a global scale, forests contribute ~50% of terrestrial net primary production and store ~45% of terrestrial carbon [5]. Over half of the water supply in the U.S. flows from forestlands [6,7]. It is estimated that tropical and temperate forests worldwide provide ecosystem goods and services of $23.32 trillion per year [8].…”