基于SHAW(Simultaneous Heat and Water)模型,以基本观测要素、植被参数和土壤剖面水热观测数据为模型的输入,对河岸胡杨林的耗水过程、土壤剖面水分变化和能通量进行了较小时间尺度上的模拟研究。结果表明,采用SHAW模型模拟的胡杨耗水...基于SHAW(Simultaneous Heat and Water)模型,以基本观测要素、植被参数和土壤剖面水热观测数据为模型的输入,对河岸胡杨林的耗水过程、土壤剖面水分变化和能通量进行了较小时间尺度上的模拟研究。结果表明,采用SHAW模型模拟的胡杨耗水量与观测值间存在较大偏差。因此,为了进一步提升水热耦合SHAW模型在干旱区的实用性,引入了地下水位因子GSI(Groundwater-Soil water Interaction),建立了改进的SHAW(GSI-SHAW)模型,解决干旱区荒漠河岸林耗水过程模拟的方法问题。采用SHAW模型和GSI-SHAW模型对胡杨耗水量的模拟进行了对比研究。结果显示,SHAW模型和GSI-SHAW模型模拟的胡杨耗水量与观测值的相关性系数分别为0.853 3、0.907 5,其平均相对误差分别为21.4%、16.9%,可见,改进的SHAW模型的模拟值更加接近试验观测值。地下水位的考虑一定程度上提升了传统SHAW模型的模拟精度,为干旱区自然植被耗水量的计算提供了新的方法和科学依据。展开更多
Net radiation (Rn), water vapor flux (LE), sensible heat flux (Hs) and soil heat flux (G)were measured above a summer maize field with the eddy-covariance technique, simulation and analysis of water, heat fluxes and c...Net radiation (Rn), water vapor flux (LE), sensible heat flux (Hs) and soil heat flux (G)were measured above a summer maize field with the eddy-covariance technique, simulation and analysis of water, heat fluxes and crop water use efficiency were made with the RZ-SHAW model at the same time in this study. The results revealed significant diurnal and seasonal variability of water vapor flux for summer maize. Most part of Rn was consumed by the evapotranspiration of the summer maize. The proportion of water vapor flux to net radiation ((LE/Rn) increased with the crop development and peaked around milk-filling stage with a value of 60%, a slightly lower than that obtained by the RZ-SHAW model. Daily evapotranspiration estimated by the model agreed with the results measured with the eddy-covariance technique, indices of agreement (IA) for hourly water vapor fluxes simulated and measured were above 0.75, root mean square errors (RMSE) were no more than 1.0. Diurnal patterns of Hs showed the shape of inverted "U" shifted to the forenoon with a maximum value around 11:30 (Beijing time), while LE exhibited an inverted "V" with a maximum value at around 13:00, about an hour later than Hs. Diurnal change of CO2showed an asymmetrical "V" curve and its maximal rates occurred at about 11:30. Variations of water use efficiency during the phonological stages of the summer maize showed a rapid increase with the photosynthetic photon flux density (PPFD) after sunrise, a state of equilibrium around 10:00 followed a decrease. Maximum values of water use efficiency were 24.3, and its average value ranged from 7.6 to 10.3 g kg-1.展开更多
Permafrost degradation is prevalent on the Qinghai-Tibet Plateau.This may lead to changes in water and heat transition in soils and thus affect the structure and function of ecosystems.In this paper,using the measured...Permafrost degradation is prevalent on the Qinghai-Tibet Plateau.This may lead to changes in water and heat transition in soils and thus affect the structure and function of ecosystems.In this paper,using the measured data of alpine steppe in Wudaoliang assessed the model performance in simulating soil freezing and thawing processes.Comparison of the simulated results by simultaneous heat and water(SHAW) model to the measured data showed that SHAW model performed satisfactorily.Based on analyzing the simulated and predicted results,two points were obtained:(1) freezing and thawing of the active layer proceeded both from the soil surface downward.Compared with the freezing process,the thawing process was slower.The freezing period persisted in the surface layer(4 cm depth) for about 5 months;(2) in the next 50 years,frozen period would be shorten about 20 days in the top 100 cm depth while the thawing would start earlier 40 days than present.Soil water storage in the 0-60 cm would decrease by 22% averagely,especially from June to August when the vegetation is at the dominating water consumed stage.Therefore,this kind of permafrost degradation as active layer freezing and thawing processes changes will reduce soil water content and thus influence those ecosystems above it.展开更多
文摘基于SHAW(Simultaneous Heat and Water)模型,以基本观测要素、植被参数和土壤剖面水热观测数据为模型的输入,对河岸胡杨林的耗水过程、土壤剖面水分变化和能通量进行了较小时间尺度上的模拟研究。结果表明,采用SHAW模型模拟的胡杨耗水量与观测值间存在较大偏差。因此,为了进一步提升水热耦合SHAW模型在干旱区的实用性,引入了地下水位因子GSI(Groundwater-Soil water Interaction),建立了改进的SHAW(GSI-SHAW)模型,解决干旱区荒漠河岸林耗水过程模拟的方法问题。采用SHAW模型和GSI-SHAW模型对胡杨耗水量的模拟进行了对比研究。结果显示,SHAW模型和GSI-SHAW模型模拟的胡杨耗水量与观测值的相关性系数分别为0.853 3、0.907 5,其平均相对误差分别为21.4%、16.9%,可见,改进的SHAW模型的模拟值更加接近试验观测值。地下水位的考虑一定程度上提升了传统SHAW模型的模拟精度,为干旱区自然植被耗水量的计算提供了新的方法和科学依据。
文摘Net radiation (Rn), water vapor flux (LE), sensible heat flux (Hs) and soil heat flux (G)were measured above a summer maize field with the eddy-covariance technique, simulation and analysis of water, heat fluxes and crop water use efficiency were made with the RZ-SHAW model at the same time in this study. The results revealed significant diurnal and seasonal variability of water vapor flux for summer maize. Most part of Rn was consumed by the evapotranspiration of the summer maize. The proportion of water vapor flux to net radiation ((LE/Rn) increased with the crop development and peaked around milk-filling stage with a value of 60%, a slightly lower than that obtained by the RZ-SHAW model. Daily evapotranspiration estimated by the model agreed with the results measured with the eddy-covariance technique, indices of agreement (IA) for hourly water vapor fluxes simulated and measured were above 0.75, root mean square errors (RMSE) were no more than 1.0. Diurnal patterns of Hs showed the shape of inverted "U" shifted to the forenoon with a maximum value around 11:30 (Beijing time), while LE exhibited an inverted "V" with a maximum value at around 13:00, about an hour later than Hs. Diurnal change of CO2showed an asymmetrical "V" curve and its maximal rates occurred at about 11:30. Variations of water use efficiency during the phonological stages of the summer maize showed a rapid increase with the photosynthetic photon flux density (PPFD) after sunrise, a state of equilibrium around 10:00 followed a decrease. Maximum values of water use efficiency were 24.3, and its average value ranged from 7.6 to 10.3 g kg-1.
基金supported by the National Basic Research Program of China(Grant No.2005CB422005)the National Basic S&T Project of China(Grant No.2006FY110200)China Postdoctoral Science Foundation(Grant No.20090460506)
文摘Permafrost degradation is prevalent on the Qinghai-Tibet Plateau.This may lead to changes in water and heat transition in soils and thus affect the structure and function of ecosystems.In this paper,using the measured data of alpine steppe in Wudaoliang assessed the model performance in simulating soil freezing and thawing processes.Comparison of the simulated results by simultaneous heat and water(SHAW) model to the measured data showed that SHAW model performed satisfactorily.Based on analyzing the simulated and predicted results,two points were obtained:(1) freezing and thawing of the active layer proceeded both from the soil surface downward.Compared with the freezing process,the thawing process was slower.The freezing period persisted in the surface layer(4 cm depth) for about 5 months;(2) in the next 50 years,frozen period would be shorten about 20 days in the top 100 cm depth while the thawing would start earlier 40 days than present.Soil water storage in the 0-60 cm would decrease by 22% averagely,especially from June to August when the vegetation is at the dominating water consumed stage.Therefore,this kind of permafrost degradation as active layer freezing and thawing processes changes will reduce soil water content and thus influence those ecosystems above it.
