張光宇博士

Postdoctoral Fellow, Lawrence Berkeley National Laboratory

Ecosystem responses to changing microclimatic conditions were investigated by comparing measured and modeled ecophysiological relationships at site-level scales. We developed an ecosystem-centric drought index, the Normalized Ecosystem Drought Index (NEDI), to quantifydrought severity presented in ecosystems. The NEDI characterizes environmental conditions into wet regime with stronger evapotranspiration (positive NEDI) and dry regime with weakerevapotranspiration (negative NEDI) by detecting ecosystem responses to water availabilityelucidated by rapid changes in localized variance. The use of NEDI was validated bymeasurements collected at 60 AmeriFlux eddy covariance sites encompassing 8 vegetation types,while the widely used Palmer Drought Severity Index (PDSI) and Standardized PrecipitationIndex (SPI) cannot capture observed ecophysiological relationships. Our model intercomparisonresults demonstrate that realistic canopy structural and functional representations can reduce theuncertainty of land surface simulation. The root mean square errors for the simulatedevapotranspiration and Net Ecosystem Exchange are reduced by 10% and 15%, respectivelywhen canopy structure is prescribed by a more realistic time-varying Leaf Area Index (LAI)dataset instead of a static LAI dataset with no geographical sensitivity. Our findings suggest that a mechanistic parameterization of biosphere-atmosphere exchanges is important to improveglobal energy and carbon budget assessments.