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Simulation and Coupling Water and Carbon Processes for Subalpine Forest Ecosystems in Southwest of Sichuan Province

Author: LiuNing
Tutor: SunPengSen
School: Chinese Academy of Forestry
Course: Ecology
Keywords: Water-Carbon coupling Ecohydrology model Hydrologial response unit Modelcalibration and validation WaSSI-C model
CLC: S718.55
Type: Master's thesis
Year: 2013
Downloads: 40
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Abstract


Comprehensive management of carbon and water resources based on the understanding andquantification of regional carbon and water coupling relationship has long been the major wayin terms of global climate change and water resource crisis on regional scale. In this study,WaSSI-C, an ecohydrological model, was employed to quantify regional water and carboncoupling relationship and to detect their spatial distribution in western Sichuan subalpine forestecosystem. The applicability and suitability of the WaSSI-C has been improved throughimproving calculation methods of evapotranspiration and snowmelt and relative developed tools.Applicability of the model was validated based on determination of the best spatial responsescale in Zagunao watershed. Spatial and seasonal variation characteristics of carbon-water fluxesand their connection with vegetation and topography were analyzed according to simulationresults, and the coupling relationship of water and carbon was also quantified, the researchesabove revealed that:（1） Improvement of the WaSSI-C model and design of the application moduleThe calculation of winter evapotranspiration （ET） was simplified for original WaSSI-Cmodel that ET and snowmelt were set as zero when air temperature was below1℃, whichwas not suitable for Zagunao watershed. The snowmelt calculation method was improved witha snowmelt-temperature linear model and the ET was derived by PET when the air temperaturewas below1℃.WaSSI-C was improved by incorporating application scheme to display simulation resultsduring calibration and validation process. This scheme included three modules: assimilation ofmulti-source data module, calibration&validation module and result showing module..（2） Determination of spatial response threshold to WaSSI-C modelDetermination of spatial response threshold is crucial to ecohydrology model andsimulation accuracy in large scale watershed. Classification schemes of different hydrological response units were conducted through setting the minimum area threshold of subbasins andtheir simulation results were contrasted by determination coefficient （R2） and Nash-Sutcliffeefficiency coefficient （NS）. The results indicated that, simulation accuracy was significantlyimpacted by spatial response scale and the optimal result was achieved when the threshold was85km2.（3） Calibration and validation of WaSSI-C modelCalibration and validation were processed comparing with original data of Zagunaowatershed after parameter sensitivity analysis. Data of1988–1996and1997–2006were used inperiods of calibration and validation respectively, during which modeled GEP and ET wascalibrated with MODIS ET and GEP data, modeled Runoff data was validated with hydrologicalstation observed data. R2and NS were calculated in order to evaluate simulation results. Incalibration period, R2of runoff and NS of runoff were0.86and0.82, respectively. And invalidation period, they were0.78and0.67, and R2of ET and GEP in this period were0.89and0.78, respectively. All these researches pointed out that the WaSSI-C model performed well inZagunao watershed.（4） Spatio-temperal dynamic and transformation between water and carbon fluxes based onWaSSI-C model in Zagunao watershedThe spatio-temperal distribution characteristic of water-carbon fluxes was significantlycorrelated with vegetation type and altitude in Zagunao watershed. It has been proved that, thealpine zone with alpine meadow as the dominant vegetation type had a high water yield (>600mm·y-1)and low ET (<420mm·y-1) and low carbon sequestration (<150g C·m-2·y-1); whilethe lower zone where evergreen the dominant vegetation type was coniferous forest or with nodominant vegetation type had a relatively lower water yield (<500mm·y-1) and higher ET(>500mm·y-1)and higher carbon sequestration(>150g C·m-2·y-1). Meanwhile, significantseasonal variation has been discovered in carbon-water fluxes, where water yield, ET, GEP, andNEE accounted for51%,50%,53%and86%respectively in the dominant season （summer）. Significantly correlation was found between water yield （RUNOFF） and net ecosystemexchange （NEE）（NEE=-0.4×RUNOFF+364.9, R2=0.84, P<0.001）. Subbasins dominatedby evergreen coniferous forest had a lower water yield and higher NEE, while subbasinsdominated by alpine meadow had a higher water yield and lower NEE.

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CLC: > Agricultural Sciences > Forestry > Forestry basic science > Forest Biology > Forest Ecology > Forest ecosystems
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