Showing papers by "Qiaozhen Mu published in 2011"

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 (R2 = 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.

Direct impacts on local climate of sugar-cane expansion in Brazil

Abstract: Expanding biofuel production into agricultural land reduces the need to clear natural ecosystems and can benefit the global climate through reduced greenhouse-gas emissions. A remote-sensing study of the Brazilian cerrado now provides empirical evidence that sugar-cane expansion also cools local climate directly by altering surface reflectivity and evapotranspiration.

Evolution of hydrological and carbon cycles under a changing climate

Abstract: Hydrological and carbon cycles are inherently coupled and play a pivotal role in the earth system. Water stress is one of the most limiting factors constraining vegetation productivity in both direct and indirect ways (mainly through nutrition cycling). In this article, we first reviewed the concepts of hydrological and carbon cycles and their interactions and then summarized recent advances in our understanding of how global climate change affects water stress, ecosystem carbon cycling, disturbances, and water use efficiency. A warming climate may continue to benefit plant growth in energy limited areas such as high latitudes and altitudes. However, over many water-limited regions of the world, a warming climate has led to a drying trend, posing negative effects on land carbon sink capability, as shown by reductions in vegetation growth and increases in ecosystem disturbances (wildfires, insect outbreaks, and tree mortality). Carbon cycle and water use efficiency have responded to climate change in different ways in different areas. Further integrating information from climate records, flux measurements at eddy flux towers, and observations from satellites will greatly advance our understanding of the hydrological and carbon cycles and their evolution. Advancement in our understanding of the evolution of hydrological and carbon cycles under the changing climate will help us to adapt and mitigate the adverse effects of climate change. Copyright © 2011 John Wiley & Sons, Ltd.

MOD16: Desafios e limitações para a estimativa global de evapotranspiração

Abstract: This article present preliminary results from the NASA’s EOS MOD16 Project, which aims to estimate global evapotranspiration (ET) using remote sensing and meteorological data. The MOD16 algorithm considers both the surface energy partitioning process and environmental constraints on ET to provide critical information on the regional and global water cycle. The objective of this research is to evaluate the version 1 of the global remote sensing evapotranspiration algorithm (MOD16). We analyzed the accuracy of the algorithm using ET observations at two eddy covariance (EC) flux tower sites in different land uses and land covers (tropical rainforest (K34) and seasonal forest (RJA)), from the Large Scale Biosphere-Atmosphere in Amazonia Project (LBA). The result shows that 8-days average, monthly ET and yearly ET are in consistent with observations of eddy covariance flux tower sites when the land cover classification is correct. However misclassification of the land cover leads to the selection of wrong parameters for vapor pressure deficit (VPD) and minimum air temperature for stomatal conductance constraints, resulting in less accurate ET estimates. The existing biases between MOD16 ET and EC observations and hydrological models may be influenced by algorithm input data, such as LAI and land cover classification. Developing a robust algorithm to estimate global ET is a significant challenge because traditionally ET models require explicit characterization of numerous surface and atmospheric parameters which are difficult to determine globally. Palavras-chave: MODIS, MOD16; evapotranspiration, tropical biomes, energy fluxes; evapotranspiração, fluxos de energia, biomas tropicais. 1. Introdução A evapotranspiração (ET) representa os processos de passagem da água do estado líquido e/ou sólido para o estado de vapor d’água atmosférico. A ET inclui a evaporação de água de superfícies líquidas, como rios e lagos, e a transpiração das plantas através das folhas. Além de ser um importante componente do ciclo hidrológico, a ET desempenha um papel Anais XV Simpósio Brasileiro de Sensoriamento Remoto SBSR, Curitiba, PR, Brasil, 30 de abril a 05 de maio de 2011, INPE p.5124