The influence of changes in vegetation type on the surface energy budget was studied using the Simple Biosphere Model (SiB) of Sellers et al. (1986). The modeled energy budget response to the conversion of forest to s...The influence of changes in vegetation type on the surface energy budget was studied using the Simple Biosphere Model (SiB) of Sellers et al. (1986). The modeled energy budget response to the conversion of forest to short vegetation or bare soil (deforestation) was investigated with SiB forced by three time--series of atmospheric boundary conditions collected at three different climatic sites: an Amazonian tropical forest, a U.S. Great Plains grassland, and a central Wales spruce forest. The results show that SiB can simulate realistic surface energy budgets and surface temperatures, and that deforestation may have a significant influellce on the local surface energy budget and surface weather. The influence is especially prominent at the Amazonian and U.S. Great Plains sites, and greater in summer than in other seasons.It was found that atmospheric boundary conditions play a dominant role in determining the degree of changes in the surface fluxes and temperature induced by deforestation; the largest change in latent heat flux appeared at the Amazon site, the largest change in sensible heat flux appeared at the Spruce forest site, and the largest change in surface temperature appeared at the Great Plains site. The Bowen ratios of the SiB sensitivity integrations for each site are comparable with observations. The values of the Bowen ratio and the ratio of latent heat flux to net radiation vary distinctly from site to site, implying that local atmospheric conditions limit the range of changes caused by the vegetation change.展开更多
The purpose of this study is to establish a depth-averaged 2-D hydrodynamic and sediment transport model for the dambreak flows with vegetation effect. The generalized shallow water equations are solved using an expli...The purpose of this study is to establish a depth-averaged 2-D hydrodynamic and sediment transport model for the dambreak flows with vegetation effect. The generalized shallow water equations are solved using an explicit finite volume method with unstructured quadtree rectangular grid, and in the hydrodynamic model, a Harten-Lax-Van Leer（HLL） approximate Riemann solver is used to calculate the intercell flux for capturing the dry-to-wet moving boundary. The sediment transport and bed variation equations in a coupled fashion are calculated by including the bed variation and the variable flow density in the flow continuity and momentum equations. The drag force of vegetation is modeled as the sink terms in the momentum equations. The developed model is tested against lab experiments of the dam-break flows over a fix bed and a movable bed in vegetated and non-vegetated channels. The results are compared with experimental data, and good agreement is obtained. It is shown that the reduced velocity under vegetated conditions leads to a decrease of the peak discharge and a rise of the water level of rivers and also an enhancement of the sediment deposition.展开更多
文摘The influence of changes in vegetation type on the surface energy budget was studied using the Simple Biosphere Model (SiB) of Sellers et al. (1986). The modeled energy budget response to the conversion of forest to short vegetation or bare soil (deforestation) was investigated with SiB forced by three time--series of atmospheric boundary conditions collected at three different climatic sites: an Amazonian tropical forest, a U.S. Great Plains grassland, and a central Wales spruce forest. The results show that SiB can simulate realistic surface energy budgets and surface temperatures, and that deforestation may have a significant influellce on the local surface energy budget and surface weather. The influence is especially prominent at the Amazonian and U.S. Great Plains sites, and greater in summer than in other seasons.It was found that atmospheric boundary conditions play a dominant role in determining the degree of changes in the surface fluxes and temperature induced by deforestation; the largest change in latent heat flux appeared at the Amazon site, the largest change in sensible heat flux appeared at the Spruce forest site, and the largest change in surface temperature appeared at the Great Plains site. The Bowen ratios of the SiB sensitivity integrations for each site are comparable with observations. The values of the Bowen ratio and the ratio of latent heat flux to net radiation vary distinctly from site to site, implying that local atmospheric conditions limit the range of changes caused by the vegetation change.
基金supported by the Public Science and Technology Research Funds Projects of Ocean(Grant No.201205023)the Program for Liaoning Province Excellent Talents in University(Grant No.LJQ2013077)+1 种基金the Science and Technology Founda-tion of Dalian City(Grant No.2013J21DW009)the Natu-ral Science Foundation of Liaoning Province(Grant No.2014020148)
文摘The purpose of this study is to establish a depth-averaged 2-D hydrodynamic and sediment transport model for the dambreak flows with vegetation effect. The generalized shallow water equations are solved using an explicit finite volume method with unstructured quadtree rectangular grid, and in the hydrodynamic model, a Harten-Lax-Van Leer（HLL） approximate Riemann solver is used to calculate the intercell flux for capturing the dry-to-wet moving boundary. The sediment transport and bed variation equations in a coupled fashion are calculated by including the bed variation and the variable flow density in the flow continuity and momentum equations. The drag force of vegetation is modeled as the sink terms in the momentum equations. The developed model is tested against lab experiments of the dam-break flows over a fix bed and a movable bed in vegetated and non-vegetated channels. The results are compared with experimental data, and good agreement is obtained. It is shown that the reduced velocity under vegetated conditions leads to a decrease of the peak discharge and a rise of the water level of rivers and also an enhancement of the sediment deposition.
