A dynamic global vegetation model （DGVM） coupled with a land surface model （LSM） is generally initialized using a spin-up process to derive a physically-consistent initial condition. Spin-up forcing, which is the ...A dynamic global vegetation model （DGVM） coupled with a land surface model （LSM） is generally initialized using a spin-up process to derive a physically-consistent initial condition. Spin-up forcing, which is the atmospheric forcing used to drive the coupled model to equilibrium solutions in the spin-up process, varies across earlier studies. In the present study, the impact of the spin-up forcing in the initialization stage on the fractional coverages （FCs） of plant functional type （PFT） in the subsequent simulation stage are assessed in seven classic climate regions by a modified Community Land Model’s Dynamic Global Vegetation Model （CLM-DGVM）. Results show that the impact of spin-up forcing is considerable in all regions except the tropical rainforest climate region （TR） and the wet temperate climate region （WM）. In the tropical monsoon climate region （TM）, the TR and TM transition region （TR-TM）, the dry temperate climate region （DM）, the highland climate region （H）, and the boreal forest climate region （BF）, where FCs are affected by climate non-negligibly, the discrepancies in initial FCs, which represent long-term cumulative response of vegetation to different climate anomalies, are large. Moreover, the large discrepancies in initial FCs usually decay slowly because there are trees or shrubs in the five regions. The intrinsic growth timescales of FCs for tree PFTs and shrub PFTs are long, and the variation of FCs of tree PFTs or shrub PFTs can affect that of grass PFTs.展开更多
Canopy interception of incident precipitation, as a critical component of a forest＇s water budget, can affect the amount of water available to the soil, and ultimately vegetation distribution and function. In this pa...Canopy interception of incident precipitation, as a critical component of a forest＇s water budget, can affect the amount of water available to the soil, and ultimately vegetation distribution and function. In this paper, a statistical-dynamic approach based on leaf area index and statistical canopy interception is used to parameterize the canopy interception process. The statistical-dynamic canopy interception scheme is implemented into the Community Land Model with dynamic global vegetation model （CLM-DGVM） to improve its dynamic vegetation simulation. The simulation for continental China by the land surface model with the new canopy interception scheme shows that the new one reasonably represents the precipitation intercepted by the canopy. Moreover, the new scheme enhances the water availability in the root zone for vegetation growth, especially in the densely vegetated and semi-arid areas, and improves the model＇s performance of potential vegetation simulation.展开更多
The statistical relationship between soil thermal anomaly and short-term climate change is presented based on a typical case study. Furthermore, possible physical mechanisms behind the relationship are re-vealed throu...The statistical relationship between soil thermal anomaly and short-term climate change is presented based on a typical case study. Furthermore, possible physical mechanisms behind the relationship are re-vealed through using an off-line land surface model with a reasonable soil thermal forcing at the bottom of the soil layer. In the first experiment, the given heat flux is 5 W m<SUP>2</SUP> at the bottom of the soil layer (in depth of 6.3 m) for 3 months, while only a positive ground temperature anomaly of 0.06°C can be found compared to the control run. The anomaly, however, could reach 0.65°C if the soil thermal conductivity was one order of magnitude larger. It could be even as large as 0.81°C assuming the heat flux at bottom is 10 W m<SUP>-2</SUP>. Mean-while, an increase of about 10 W m<SUP>−2</SUP> was detected both for heat flux in soil and sensible heat on land sur-face, which is not neglectable to the short-term climate change. The results show that considerable response in land surface energy budget could be expected when the soil thermal forcing reaches a certain spatial-tem-poral scale. Therefore, land surface models should not ignore the upward heat flux from the bottom of the soil layer. Moreover, integration for a longer period of time and coupled land-atmosphere model are also necessary for the better understanding of this issue.展开更多
In this study,a new parameter optimization method was used to investigate the expansion of conditional nonlinear optimal perturbation （CNOP） in a land surface model （LSM） using long-term enhanced field observation...In this study,a new parameter optimization method was used to investigate the expansion of conditional nonlinear optimal perturbation （CNOP） in a land surface model （LSM） using long-term enhanced field observations at Tongyu station in Jilin Province,China,combined with a sophisticated LSM （common land model,CoLM）.Tongyu station is a reference site of the international Coordinated Energy and Water Cycle Observations Project （CEOP） that has studied semiarid regions that have undergone desertification,salination,and degradation since late 1960s.In this study,three key land-surface parameters,namely,soil color,proportion of sand or clay in soil,and leaf-area index were chosen as parameters to be optimized.Our study comprised three experiments：First,a single-parameter optimization was performed,while the second and third experiments performed triple-and six-parameter optimizations,respectively.Notable improvements in simulating sensible heat flux （SH）,latent heat flux （LH）,soil temperature （TS）,and moisture （MS） at shallow layers were achieved using the optimized parameters.The multiple-parameter optimization experiments performed better than the single-parameter experminent.All results demonstrate that the CNOP method can be used to optimize expanded parameters in an LSM.Moreover,clear mathematical meaning,simple design structure,and rapid computability give this method great potential for further application to parameter optimization in LSMs.展开更多
Nitrogen cycling has profound effects on carbon uptake in the terrestrial ecosystem and the response of the biosphere to climate changes.However,nutrient cycling is not taken into account in most land surface models f...Nitrogen cycling has profound effects on carbon uptake in the terrestrial ecosystem and the response of the biosphere to climate changes.However,nutrient cycling is not taken into account in most land surface models for climate change.In this study,a nitrogen model,based on nitrogen transformation processes and nitrogen fluxes exchange between the atmosphere and terrestrial ecosystem,was incorporated into the Atmosphere–Vegetation Interaction Model(AVIM)to simulate the carbon cycle under nitrogen limitation.This new model,AVIM-CN,was evaluated against site-scale eddy covariance–based measurements of an alpine meadow located at Damxung station from the FLUXNET 2015 dataset.Results showed that the annual mean gross primary production simulated by AVIM-CN(0.7073 gC m^-2 d^-1)was in better agreement with the corresponding flux data(0.5407 gC m^-2 d^-1)than the original AVIM(1.1403 gC m^-2 d^-1)at Damxung station.Similarly,ecosystem respiration was also down-regulated,from 1.7695 gC m^-2 d^-1 to 1.0572 gC m^-2 d^-1,after the nitrogen processes were introduced,and the latter was closer to the observed vales(0.8034 gC m^-2 d^-1).Overall,the new results were more consistent with the daily time series of carbon and energy fluxes of observations compared to the former version without nitrogen dynamics.A model that does not incorporate the limitation effects of nitrogen nutrient availability will probably overestimate carbon fluxes by about 40%.展开更多
Mountains are important suppliers of freshwater to downstream areas,affecting large populations in particular in High Mountain Asia(HMA).Yet,the propagation of water from HMA headwaters to downstream areas is not full...Mountains are important suppliers of freshwater to downstream areas,affecting large populations in particular in High Mountain Asia(HMA).Yet,the propagation of water from HMA headwaters to downstream areas is not fully understood,as interactions in the mountain water cycle between the cryo-,hydro-and biosphere remain elusive.We review the definition of blue and green water fluxes as liquid water that contributes to runoff at the outlet of the selected domain(blue)and water lost to the atmosphere through vapor fluxes,that is evaporation from water,ground,and interception plus transpiration(green)and propose to add the term white water to account for the(often neglected)evaporation and sublimation from snow and ice.We provide an assessment of models that can simulate the cryo-hydro-biosphere continuum and the interactions between spheres in high mountain catchments,going beyond disciplinary separations.Land surface models are uniquely able to account for such complexity,since they solve the coupled fluxes of water,energy,and carbon between the land surface and atmosphere.Due to the mechanistic nature of such models,specific variables can be compared systematically to independent remote sensing observations-providing vital insights into model accuracy and enabling the understanding of the complex watersheds of HMA.We discuss recent developments in spaceborne earth observation products that have the potential to support catchment modeling in high mountain regions.We then present a pilot study application of the mechanistic land surface model Tethys&Chloris to a glacierized watershed in the Nepalese Himalayas and discuss the use of high-resolution earth observation data to constrain the meteorological forcing uncertainty and validate model results.We use these insights to highlight the remaining challenges and future opportunities that remote sensing data presents for land surface modeling in HMA.展开更多
In Earth system modeling,the land surface is coupled with the atmosphere through surface turbulent fluxes.These fluxes are computed using mean meteorological variables between the surface and a reference height in the...In Earth system modeling,the land surface is coupled with the atmosphere through surface turbulent fluxes.These fluxes are computed using mean meteorological variables between the surface and a reference height in the atmosphere.However,the dependence of flux computation on the reference height,which is usually set as the lowest level in the atmosphere in Earth system models,has not received much attention.Based on high-resolution large-eddy simulation(LES)data under unstable conditions,we find the setting of reference height is not trivial within the framework of current surface layer theory.With a reasonable prescription of aerodynamic roughness length(following the setting in LESs),reference heights near the top of the surface layer tend to provide the best estimate of surface fluxes,especially for the momentum flux.Furthermore,this conclusion for the sensible heat flux is insensitive to the ratio of roughness length for momentum versus heat.These results are robust,whether using the classical or revised surface layer theory.They provide a potential guide for setting the proper reference heights for Earth system modeling and can be further tested in the near future using observational data from land–atmosphere feedback observatories.展开更多
The IAP (Institute of Atmospheric Physics) land-surface model (IAP94) is described. This model is a comprehensive one with detailed description for the processes of vegetation, snow and soil. Particular attention has ...The IAP (Institute of Atmospheric Physics) land-surface model (IAP94) is described. This model is a comprehensive one with detailed description for the processes of vegetation, snow and soil. Particular attention has been paid to the cases with three water phases in the surface media. On the basis of the mixture theory and the theory of fluid dynamics of porous media, the system of universal conservational equations for water and heat of soil, snow and vegetation canopy has been constructed. On this background, all important factors that may affect the water and heat balance in media can be considered naturally, and each factor and term possess distinct physical meaning. In the computation of water content and temperature, the water phase change and the heat transportation by water flow are taken into account. Moreover, particular attention has been given to the water vapor diffusion in soil for arid or semi-arid cases, and snow compaction. In the treatment of surface turbulent fluxes, the difference between aerodynamic and thermal roughness is taken into account. The aerodynamic roughness of vegetation is calculated as a function of canopy density, height and zero-plane displacement. An extrapolation of log linear and exponential relationship is used when calculating the wind profile within canopy. The model has been validated against field measurements in off-line simulations. The desirable model′s performance leads to the conclusion that the IAP94 is able to reproduce the main physical mechanisms governing the energy and water balances in the global land surface. Part II of the present study will concern the validation in a 3-D experiment coupled with the IAP Two-Level AGCM.展开更多
Land surface process is of great importance in global climate change,moisture and heat exchange in the interface of the earth and atmosphere,human impacts on the environment and eco-system,etc.Soil freeze/thaw plays a...Land surface process is of great importance in global climate change,moisture and heat exchange in the interface of the earth and atmosphere,human impacts on the environment and eco-system,etc.Soil freeze/thaw plays an important role in cold land surface processes.In this work the diurnal freeze/thaw effects on energy partition in the context of GAME/Tibet are studied.A sophisti-cated land surface model is developed,the particular aspect of which is its physical consideration of soil freeze/thaw and vapor flux.The simultaneous water and heat transfer soil sub-model not only reflects the water flow from unfrozen zone to frozen fringe in freezing/thawing soil,but also demon-strates the change of moisture and temperature field induced by vapor flux from high temperature zone to low temperature zone,which makes the model applicable for various circumstances.The modified Picard numerical method is employed to help with the water balance and convergence of the numerical scheme.Finally,the model is applied to analyze the diurnal energy and water cycle char-acteristics over the Tibetan Plateau using the Game/Tibet datasets observed in May and July of 1998.Heat and energy transfer simulation shows that:(i)There exists a negative feedback mechanism between soil freeze/thaw and soil temperature/ground heat flux;(ii)during freezing period all three heat fluxes do not vary apparently,in spite of the fact that the negative soil temperature is higher than that not considering soil freeze;(iii)during thawing period,ground heat flux increases,and sensible heat flux decreases,but latent heat flux does not change much;and(iv)during freezing period,soil temperature decreases,though ground heat flux increases.展开更多
In order to examine and analyze the effects of integration of land surface models with TOPMODEL and different approaches for the integration on the model simulation of water and energy balances,the coupled models have...In order to examine and analyze the effects of integration of land surface models with TOPMODEL and different approaches for the integration on the model simulation of water and energy balances,the coupled models have been developed,which incorporate TOPMODEL into the Simplified Biosphere Model(SSiB) with different approaches(one divides a basin into a number of zones according to the distribution of topographic index,and the other only divides the basin into saturated and unsaturated zones).The coupled models are able to(but SSiB is not able to) take into account the impacts of topography variation and vertical heterogeneity of soil saturated hydraulic conductivity on horizontal distribution of soil moisture and in turn on water and energy balances within the basin(or a grid cell).By using the coupled models and SSiB model itself,the daily hydrological components such as runoffs are simulated and final results are analyzed carefully.Simulated daily results of hydrological components produced by both SSiB and coupled models show that(i) There is significant difference between results of soil wetness,its vertical distribution and seasonal variation,water and energy balance,and daily runoff in the basin predicted by SSiB and by the coupled models.The land surface model currently used such as SSiB is likely to misrepresent real feature of water and energy balances in the basin.(ii) Compared with the results for the basin predicted by SSiB,the coupled models predict more strong vertical and seasonal changes in soil wetness,higher evaporation and lower runoff,and improve the base flow simulation obviously.(iii) Comparing the results for the basin predicted by two coupled models with different integration approach and SSiB one by one,the results of daily runoffs and soil wetness predicted by the two coupled models are quite similar.It means,for the coupled models,the approach by dividing a region being considered into more subzones may have limited effects on improving runoff simulation results.The scheme only to divide the region into saturated and unsaturated zones may be a convenient and effective scheme.But then,if the results from the two coupled models for the basin are carefully compared,the simulated results by the coupled model with dividing the basin into more subzones will show higher evaporation and surface runoff but lower subsurface flow,lower total runoff,and lower ground water level averaged for five years.展开更多
In order to compare the impacts of the choice of land surface model(LSM)parameterization schemes,meteorological forcing,and land surface parameters on land surface hydrological simulations,and explore to what extent t...In order to compare the impacts of the choice of land surface model(LSM)parameterization schemes,meteorological forcing,and land surface parameters on land surface hydrological simulations,and explore to what extent the quality can be improved,a series of experiments with different LSMs,forcing datasets,and parameter datasets concerning soil texture and land cover were conducted.Six simulations are run for the Chinese mainland on 0.1°×0.1°grids from 1979 to 2008,and the simulated monthly soil moisture(SM),evapotranspiration(ET),and snow depth(SD)are then compared and assessed against observations.The results show that the meteorological forcing is the most important factor governing output.Beyond that,SM seems to be also very sensitive to soil texture information;SD is also very sensitive to snow parameterization scheme in the LSM.The Community Land Model version 4.5(CLM4.5),driven by newly developed observation-based regional meteorological forcing and land surface parameters(referred to as CMFD_CLM4.5_NEW),significantly improved the simulations in most cases over the Chinese mainland and its eight basins.It increased the correlation coefficient values from 0.46 to 0.54 for the SM modeling and from 0.54 to 0.67 for the SD simulations,and it decreased the root-mean-square error(RMSE)from 0.093 to 0.085 for the SM simulation and reduced the normalized RMSE from 1.277 to 0.201 for the SD simulations.This study indicates that the offline LSM simulation using a refined LSM driven by newly developed observation-based regional meteorological forcing and land surface parameters can better model reginal land surface hydrological processes.展开更多
The authors examined the performance of version 3.4.1 of the Weather Research and Forecasting Model(WRF) with various land surface schemes in simulating a severe drought event in Southwest China. Five numerical experi...The authors examined the performance of version 3.4.1 of the Weather Research and Forecasting Model(WRF) with various land surface schemes in simulating a severe drought event in Southwest China. Five numerical experiments were completed using the Noah land surface scheme, the Pleim-Xiu land surface scheme, the Noah-MP land surface schemes, the Noah- MP scheme with dynamic vegetation, and the Noah-MP scheme with dynamic vegetation and groundwater processes. In general, all the simulations reasonably reproduced the spatial and temporal variations in precipitation, but significant bias was also found, especially for the spatial pattern of simulated precipitation. The WRF simulations with the Noah-MP series land surface schemes performed slightly better than the WRF simulation with the Noah and Pleim-Xiu land surface schemes in reproducing the severe drought events in Southwest China. The leaf area index(LAI) simulated by the different land surface schemes showed significant deviations in Southwest China. The Pleim-Xiu scheme overestimated the value of LAI by a factor of two. The Noah-MP scheme with dynamical vegetation overestimated the magnitude of the annual cycle of the LAI, although the annual mean LAI was close to observations. The simulated LAI showed a long-term lower value from autumn 2009 to spring 2010 relative to normal years. This indicates that the LAI is a potential indictor to monitor drought events.展开更多
In this paper, the global and regional features of the seasonal variation of general circulation, and especially the Asian monsoon simulated by the Institute of Atmospheric Physics Two-level AGCM coupled with a sophis...In this paper, the global and regional features of the seasonal variation of general circulation, and especially the Asian monsoon simulated by the Institute of Atmospheric Physics Two-level AGCM coupled with a sophisticated land-surface model (IAP94-GCM) are presented and compared with the observation. The comparison is made by using the equilibrium multiyear seasonal cycle climate from a 100-year integration. In the integration sea surface temperature (SST) and sea ice are taken from the observed climatological data (with seasonal variation) because our purpose is to see the improvement of simulation due to the coupling with an advanced land surface model. Overall, the IAP94-GCM provides a reasonably realistic simulation of the interseasonal and intraseasonal climatology of the Asian monsoon and yields an important information that sheds light on the thermal underpinning and the thermodynamics of the seasonal and even multiscale variabilities associated with the Asian summer monsoon.展开更多
The Institute of Atmospheric Physics Land Surface Model (IAP94) has been incorporated into the IAP two-level atmospheric general circulation model (IAP GCM). Global and regional climatology averaged over the last 25 y...The Institute of Atmospheric Physics Land Surface Model (IAP94) has been incorporated into the IAP two-level atmospheric general circulation model (IAP GCM). Global and regional climatology averaged over the last 25 years of 100 year integrations from the IAP GCM with and without IAP94 (“bucket” scheme) is compared. The simulated results are also compared with the reanalysis data. Major findings are: \ \ (1) The IAP GCM simulation without IAP94 has extensive regions of warmer than observed surface air temperatures, while the simulation with IAP94 very much improves the surface air temperature. \ \ (2) The IAP GCM simulation with IAP94 gives improvement of the simulated precipitation pattern and intensity, especially the precipitation of East Asian summer monsoon and its intraseasonal migration of the rainbelts. \ \ (3) In five selected typical regions, for most of the surface variables such as surface air temperature, precipitation, precipitation minus evaporation, net radiation, latent heat flux and sensible heat flux, the IAP GCM with IAP94 provides better simulations.展开更多
Two land surface models, Community Land Model (CLM3.5) and NOAH model, have been coupled to the Weather Research and Forecasting (WRF) model and been used to simulate the precipitation, temperature, and circulation fi...Two land surface models, Community Land Model (CLM3.5) and NOAH model, have been coupled to the Weather Research and Forecasting (WRF) model and been used to simulate the precipitation, temperature, and circulation fields, respectively, over eastern China in a typical flood year (1998). The purpose of this study is to reveal the effects of land surface changes on regional climate modeling. Comparisons of simulated results and observation data indicate that changes in land surface processes have significant impact on spatial and temporal distribution of precipitation and temperature patterns in eastern China. Coupling of the CLM3.5 to the WRF model (experiment WRF-C) substantially improves the simulation results over eastern China relative to an older version of WRF coupled to the NOAH-LSM (experiment WRF-N). It is found that the simulation of the spatial pattern of summer precipitation in WRF-C is better than in WRF-N. WRF-C also significantly reduces the summer positive bias of surface air temperature, and its simulated surface air temperature matches more closely to observations than WRF-N does, which is associated with lower sensible heat fluxes and higher latent heat fluxes in WRF-C.展开更多
Land data assimilation(DA)is an effective method to provide high-quality spatially and temporally continuous soil moisture datasets that are crucial in weather,climate,hydrological,and agricultural research.However,mo...Land data assimilation(DA)is an effective method to provide high-quality spatially and temporally continuous soil moisture datasets that are crucial in weather,climate,hydrological,and agricultural research.However,most existing land DA applications have used remote sensing observations,and are based on one-dimensional(1 D)analysis,which cannot be directly employed to reasonably assimilate the recently expanded in-situ soil moisture observations in China.In this paper,a two-dimensional(2 D)localized ensemble-based optimum interpolation(En OI)scheme for assimilating in-situ soil moisture observations from over 2200 stations into land surface models(LSMs)is introduced.This scheme uses historical LSM simulations as ensemble samples to provide soil moisture background error covariance,allowing the in-situ observation information to be propagated to surrounding pixels.It is also computationally efficient because no additional ensemble simulations are needed.A set of ensemble sampling and localization length scale sensitivity experiments are performed.The En OI performs best for in-situ soil moisture fusion over China with an ensemble sampling of hourly soil moisture from the previous 7 days and a localization length scale of 100 km.Following the evaluation,simulations for in-situ soil moisture fusion are also performed from May 2016 to September 2016.The En OI analysis is notably better than that without in-situ observation fusion,as the wet bias of 0.02 m3 m-3 is removed,the root-mean-square error(RMSE)is reduced by about 37%,and the correlation coefficient is increased by about 25%.Independent evaluation shows that the En OI analysis performs considerably better than that without fusion in terms of bias,and marginally better in terms of RMSE and correlation.展开更多
In this paper,the complex land surface model BATSle was coupled to the PSU/NCAR MMSV3.And the coupled model was used to simulate the heavy rain in summers of 1991 and 1998.The results show that,with the detailed land ...In this paper,the complex land surface model BATSle was coupled to the PSU/NCAR MMSV3.And the coupled model was used to simulate the heavy rain in summers of 1991 and 1998.The results show that,with the detailed land surface parameterization,the model can (1) simulate the distribution of heavy rain in Yangtze River Basin in summers of 1991 and 1998 more precisely,and improve the results by increasing the simulated precipitation rate;(2)improve the simulation results of surface temperature:(3)improve the simulation results of the circulation and temperature fields at middle and high levels.展开更多
Surface runoff is mainly generated by two mechanisms, infiltration excess (Horton) runoff and saturation excess (Dunne) runoff; and the spatial variability of soil properties, antecedent soil moisture, topography, and...Surface runoff is mainly generated by two mechanisms, infiltration excess (Horton) runoff and saturation excess (Dunne) runoff; and the spatial variability of soil properties, antecedent soil moisture, topography, and rainfall will result in different surface runoff generation mechanisms. For a large area (e.g., a model grid size of a regional climate model or a general circulation model), these runoff generation mechanisms are commonly present at different portions of a grid cell simultaneously. Missing one of the two major runoff generation mechanisms and failing to consider spatial soil variability can result in significant under/over estimation of surface runoff which can directly introduce large errors in soil moisture states over each model grid cell. Therefore, proper modeling of surface runoff is essential to a reasonable representation of feedbacks in a land-atmosphere system. This paper presents a new surface runoff parameterization with the Philip infiltration formulation that dynamically represents both the Horton and Dunne runoff generation mechanisms within a model grid cell. The parameterization takes into account the effects of soil heterogeneity on Horton and Dunne runoff. The new parameterization is implemented into the current version of the hydrologically based Variable Infiltration Capacity (VIC) land surface model and tested over one watershed in Pennsylvania, USA and over the Shiguanhe Basin in the Huaihe Watershed in China. Results show that the new parameterization plays a very important role in partitioning the water budget between surface runoff and soil moisture in the atmosphere-land coupling system, and has potential applications on large hydrological simulations and land-atmospheric interactions. It is further found that the Horton runoff mechanism should be considered within the context of subgrid-scale spatial variability of soil properties and precipitation.展开更多
In this study, the Crop Estimation through Resource and Environment Synthesis model （CERES3.0） was coupled into the Biosphere-Atmosphere Transfer Scheme （BATS）, which is called BATS CERES, to represent interaction...In this study, the Crop Estimation through Resource and Environment Synthesis model （CERES3.0） was coupled into the Biosphere-Atmosphere Transfer Scheme （BATS）, which is called BATS CERES, to represent interactions between the land surface and crop growth processes. The effects of crop growth and development on land surface processes were then studied based on numerical simulations using the land surface models. Six sensitivity experiments by BATS show that the land surface fluxes underwent substantial changes when the leaf area index was changed from 0 to 6 m2 m-2. Numerical experiments for Yucheng and Taoyuan stations reveal that the coupled model could capture not only the responses of crop growth and development to environmental conditions, but also the feedbacks to land surface processes. For quantitative evaluation of the effects of crop growth and development on surface fluxes in China, two numerical experiments were conducted over continental China： one by BATS CERES and one by the original BATS. Comparison of the two runs shows decreases of leaf area index and fractional vegetation cover when incorporating dynamic crops in land surface simulation, which lead to less canopy interception, vegetation transpiration, total evapotranspiration, top soil moisture, and more soil evaporation, surface runoff, and root zone soil moisture. These changes are accompanied by decreasing latent heat flux and increasing sensible heat flux in the cropland region. In addition, the comparison between the simulations and observations proved that incorporating the crop growth and development process into the land surface model could reduce the systematic biases of the simulated leaf area index and top soil moisture, hence improve the simulation of land surface fluxes.展开更多
As part of a joint effort to construct an atmospheric forcing dataset for China's Mainland with high spatiotemporal reso- lution, a new approach is proposed to construct gridded near-surface temperature, relative ...As part of a joint effort to construct an atmospheric forcing dataset for China's Mainland with high spatiotemporal reso- lution, a new approach is proposed to construct gridded near-surface temperature, relative humidity, wind speed and surface pressure with a resolution of 1 km× 1 km. The approach comprises two steps： （1） fit a partial thin-plate smoothing spline with orography and reanalysis data as explanatory variables to ground-based observations for estimating a trend surface; （2） apply a simple kriging procedure to the residual for trend surface correction. The proposed approach is applied to observations collected at approximately 700 stations over China's Mainland. The generated forcing fields are compared with the corresponding components of the National Centers for Environmental Predic- tion （NCEP） Climate Forecast System Reanalysis dataset and the Princeton meteorological forcing dataset. The comparison shows that, both within the station network and within the resolutions of the two gridded datasets, the interpolation errors of the proposed approach are markedly smaller than the two gridded datasets.展开更多
基金supported by the Chinese Academy of Sciences under Grant No.KZCX2-YW-219State Key Project for Basic Research Program of China(973)under Grant No.2010CB951801Key Program of National Natural Science Foundation under Grant No.40830103
文摘A dynamic global vegetation model （DGVM） coupled with a land surface model （LSM） is generally initialized using a spin-up process to derive a physically-consistent initial condition. Spin-up forcing, which is the atmospheric forcing used to drive the coupled model to equilibrium solutions in the spin-up process, varies across earlier studies. In the present study, the impact of the spin-up forcing in the initialization stage on the fractional coverages （FCs） of plant functional type （PFT） in the subsequent simulation stage are assessed in seven classic climate regions by a modified Community Land Model’s Dynamic Global Vegetation Model （CLM-DGVM）. Results show that the impact of spin-up forcing is considerable in all regions except the tropical rainforest climate region （TR） and the wet temperate climate region （WM）. In the tropical monsoon climate region （TM）, the TR and TM transition region （TR-TM）, the dry temperate climate region （DM）, the highland climate region （H）, and the boreal forest climate region （BF）, where FCs are affected by climate non-negligibly, the discrepancies in initial FCs, which represent long-term cumulative response of vegetation to different climate anomalies, are large. Moreover, the large discrepancies in initial FCs usually decay slowly because there are trees or shrubs in the five regions. The intrinsic growth timescales of FCs for tree PFTs and shrub PFTs are long, and the variation of FCs of tree PFTs or shrub PFTs can affect that of grass PFTs.
文摘Canopy interception of incident precipitation, as a critical component of a forest＇s water budget, can affect the amount of water available to the soil, and ultimately vegetation distribution and function. In this paper, a statistical-dynamic approach based on leaf area index and statistical canopy interception is used to parameterize the canopy interception process. The statistical-dynamic canopy interception scheme is implemented into the Community Land Model with dynamic global vegetation model （CLM-DGVM） to improve its dynamic vegetation simulation. The simulation for continental China by the land surface model with the new canopy interception scheme shows that the new one reasonably represents the precipitation intercepted by the canopy. Moreover, the new scheme enhances the water availability in the root zone for vegetation growth, especially in the densely vegetated and semi-arid areas, and improves the model＇s performance of potential vegetation simulation.
基金This paper is jointly sponsored by China NKBRSF Project G1999043400,National Natural Science Foundationof China under Grant Nos.49835010and 40075019,and China Post Doctoral Science Foundation.
文摘The statistical relationship between soil thermal anomaly and short-term climate change is presented based on a typical case study. Furthermore, possible physical mechanisms behind the relationship are re-vealed through using an off-line land surface model with a reasonable soil thermal forcing at the bottom of the soil layer. In the first experiment, the given heat flux is 5 W m<SUP>2</SUP> at the bottom of the soil layer (in depth of 6.3 m) for 3 months, while only a positive ground temperature anomaly of 0.06°C can be found compared to the control run. The anomaly, however, could reach 0.65°C if the soil thermal conductivity was one order of magnitude larger. It could be even as large as 0.81°C assuming the heat flux at bottom is 10 W m<SUP>-2</SUP>. Mean-while, an increase of about 10 W m<SUP>−2</SUP> was detected both for heat flux in soil and sensible heat on land sur-face, which is not neglectable to the short-term climate change. The results show that considerable response in land surface energy budget could be expected when the soil thermal forcing reaches a certain spatial-tem-poral scale. Therefore, land surface models should not ignore the upward heat flux from the bottom of the soil layer. Moreover, integration for a longer period of time and coupled land-atmosphere model are also necessary for the better understanding of this issue.
基金supported by National Natural Science Foundation of China (Grant Nos. 40775050,40975049,and 40810059003)National Basic Research Program of China (Grant No.2011CB952002)
文摘In this study,a new parameter optimization method was used to investigate the expansion of conditional nonlinear optimal perturbation （CNOP） in a land surface model （LSM） using long-term enhanced field observations at Tongyu station in Jilin Province,China,combined with a sophisticated LSM （common land model,CoLM）.Tongyu station is a reference site of the international Coordinated Energy and Water Cycle Observations Project （CEOP） that has studied semiarid regions that have undergone desertification,salination,and degradation since late 1960s.In this study,three key land-surface parameters,namely,soil color,proportion of sand or clay in soil,and leaf-area index were chosen as parameters to be optimized.Our study comprised three experiments：First,a single-parameter optimization was performed,while the second and third experiments performed triple-and six-parameter optimizations,respectively.Notable improvements in simulating sensible heat flux （SH）,latent heat flux （LH）,soil temperature （TS）,and moisture （MS） at shallow layers were achieved using the optimized parameters.The multiple-parameter optimization experiments performed better than the single-parameter experminent.All results demonstrate that the CNOP method can be used to optimize expanded parameters in an LSM.Moreover,clear mathematical meaning,simple design structure,and rapid computability give this method great potential for further application to parameter optimization in LSMs.
基金supported by a project of the National Key Research and Development Program of China [grant number2016YFA0602501]a project of the National Natural Science Foundation of China [grant numbers 41630532 and41575093]
文摘Nitrogen cycling has profound effects on carbon uptake in the terrestrial ecosystem and the response of the biosphere to climate changes.However,nutrient cycling is not taken into account in most land surface models for climate change.In this study,a nitrogen model,based on nitrogen transformation processes and nitrogen fluxes exchange between the atmosphere and terrestrial ecosystem,was incorporated into the Atmosphere–Vegetation Interaction Model(AVIM)to simulate the carbon cycle under nitrogen limitation.This new model,AVIM-CN,was evaluated against site-scale eddy covariance–based measurements of an alpine meadow located at Damxung station from the FLUXNET 2015 dataset.Results showed that the annual mean gross primary production simulated by AVIM-CN(0.7073 gC m^-2 d^-1)was in better agreement with the corresponding flux data(0.5407 gC m^-2 d^-1)than the original AVIM(1.1403 gC m^-2 d^-1)at Damxung station.Similarly,ecosystem respiration was also down-regulated,from 1.7695 gC m^-2 d^-1 to 1.0572 gC m^-2 d^-1,after the nitrogen processes were introduced,and the latter was closer to the observed vales(0.8034 gC m^-2 d^-1).Overall,the new results were more consistent with the daily time series of carbon and energy fluxes of observations compared to the former version without nitrogen dynamics.A model that does not incorporate the limitation effects of nitrogen nutrient availability will probably overestimate carbon fluxes by about 40%.
基金supported by the ESA and NRSCC Dragon 5 cooperation project“Cryosphere-hydrosphere interactions of the Asian water towers:using remote sensing to drive hyper-resolution ecohydrological modelling”[Grant no.59199]PB and FP acknowledge funding from the SNSF(High-elevation precipitation in High Mountain Asia,HOPE)[Grant no.183633]+4 种基金ESM,MK,SFu and FP acknowledge funding from the ERC under the European Union’s Horizon 2020 research and innovation program(Rapid mass losses of debris-covered glaciers in High Mountain Asia,RAVEN)[Grant no.772751]LJ,CZ and MMe acknowledge the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)[grant no.2019QZKK010308,no.2019QZKK0206]the National Natural Science Foundation of China projects(Grant no.42171039,no.91737205)the Chinese Academy of Sciences President’s International Fellowship Initiative[Grant no.2020VTA0001]the MOST High-Level Foreign Expert Program[Grant no.G2022055010L].
文摘Mountains are important suppliers of freshwater to downstream areas,affecting large populations in particular in High Mountain Asia(HMA).Yet,the propagation of water from HMA headwaters to downstream areas is not fully understood,as interactions in the mountain water cycle between the cryo-,hydro-and biosphere remain elusive.We review the definition of blue and green water fluxes as liquid water that contributes to runoff at the outlet of the selected domain(blue)and water lost to the atmosphere through vapor fluxes,that is evaporation from water,ground,and interception plus transpiration(green)and propose to add the term white water to account for the(often neglected)evaporation and sublimation from snow and ice.We provide an assessment of models that can simulate the cryo-hydro-biosphere continuum and the interactions between spheres in high mountain catchments,going beyond disciplinary separations.Land surface models are uniquely able to account for such complexity,since they solve the coupled fluxes of water,energy,and carbon between the land surface and atmosphere.Due to the mechanistic nature of such models,specific variables can be compared systematically to independent remote sensing observations-providing vital insights into model accuracy and enabling the understanding of the complex watersheds of HMA.We discuss recent developments in spaceborne earth observation products that have the potential to support catchment modeling in high mountain regions.We then present a pilot study application of the mechanistic land surface model Tethys&Chloris to a glacierized watershed in the Nepalese Himalayas and discuss the use of high-resolution earth observation data to constrain the meteorological forcing uncertainty and validate model results.We use these insights to highlight the remaining challenges and future opportunities that remote sensing data presents for land surface modeling in HMA.
基金supported by the Natural Science Foundation of China(Grant Nos.42088101 and 42375163)the Guangdong Major Project of Basic and Applied Basic Research(Grant No.2021B0301030007)the specific research fund of The Innovation Platform for Academicians of Hainan Province(Grant No.YSPTZX202143)。
文摘In Earth system modeling,the land surface is coupled with the atmosphere through surface turbulent fluxes.These fluxes are computed using mean meteorological variables between the surface and a reference height in the atmosphere.However,the dependence of flux computation on the reference height,which is usually set as the lowest level in the atmosphere in Earth system models,has not received much attention.Based on high-resolution large-eddy simulation(LES)data under unstable conditions,we find the setting of reference height is not trivial within the framework of current surface layer theory.With a reasonable prescription of aerodynamic roughness length(following the setting in LESs),reference heights near the top of the surface layer tend to provide the best estimate of surface fluxes,especially for the momentum flux.Furthermore,this conclusion for the sensible heat flux is insensitive to the ratio of roughness length for momentum versus heat.These results are robust,whether using the classical or revised surface layer theory.They provide a potential guide for setting the proper reference heights for Earth system modeling and can be further tested in the near future using observational data from land–atmosphere feedback observatories.
文摘The IAP (Institute of Atmospheric Physics) land-surface model (IAP94) is described. This model is a comprehensive one with detailed description for the processes of vegetation, snow and soil. Particular attention has been paid to the cases with three water phases in the surface media. On the basis of the mixture theory and the theory of fluid dynamics of porous media, the system of universal conservational equations for water and heat of soil, snow and vegetation canopy has been constructed. On this background, all important factors that may affect the water and heat balance in media can be considered naturally, and each factor and term possess distinct physical meaning. In the computation of water content and temperature, the water phase change and the heat transportation by water flow are taken into account. Moreover, particular attention has been given to the water vapor diffusion in soil for arid or semi-arid cases, and snow compaction. In the treatment of surface turbulent fluxes, the difference between aerodynamic and thermal roughness is taken into account. The aerodynamic roughness of vegetation is calculated as a function of canopy density, height and zero-plane displacement. An extrapolation of log linear and exponential relationship is used when calculating the wind profile within canopy. The model has been validated against field measurements in off-line simulations. The desirable model′s performance leads to the conclusion that the IAP94 is able to reproduce the main physical mechanisms governing the energy and water balances in the global land surface. Part II of the present study will concern the validation in a 3-D experiment coupled with the IAP Two-Level AGCM.
基金This research was supported by the National Natural Science Foundation of China(Grant No.49971002)Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.20020003049).
文摘Land surface process is of great importance in global climate change,moisture and heat exchange in the interface of the earth and atmosphere,human impacts on the environment and eco-system,etc.Soil freeze/thaw plays an important role in cold land surface processes.In this work the diurnal freeze/thaw effects on energy partition in the context of GAME/Tibet are studied.A sophisti-cated land surface model is developed,the particular aspect of which is its physical consideration of soil freeze/thaw and vapor flux.The simultaneous water and heat transfer soil sub-model not only reflects the water flow from unfrozen zone to frozen fringe in freezing/thawing soil,but also demon-strates the change of moisture and temperature field induced by vapor flux from high temperature zone to low temperature zone,which makes the model applicable for various circumstances.The modified Picard numerical method is employed to help with the water balance and convergence of the numerical scheme.Finally,the model is applied to analyze the diurnal energy and water cycle char-acteristics over the Tibetan Plateau using the Game/Tibet datasets observed in May and July of 1998.Heat and energy transfer simulation shows that:(i)There exists a negative feedback mechanism between soil freeze/thaw and soil temperature/ground heat flux;(ii)during freezing period all three heat fluxes do not vary apparently,in spite of the fact that the negative soil temperature is higher than that not considering soil freeze;(iii)during thawing period,ground heat flux increases,and sensible heat flux decreases,but latent heat flux does not change much;and(iv)during freezing period,soil temperature decreases,though ground heat flux increases.
基金supported by National Natural Science Foundation of China(Grant Nos.41075060 and 41030106)
文摘In order to examine and analyze the effects of integration of land surface models with TOPMODEL and different approaches for the integration on the model simulation of water and energy balances,the coupled models have been developed,which incorporate TOPMODEL into the Simplified Biosphere Model(SSiB) with different approaches(one divides a basin into a number of zones according to the distribution of topographic index,and the other only divides the basin into saturated and unsaturated zones).The coupled models are able to(but SSiB is not able to) take into account the impacts of topography variation and vertical heterogeneity of soil saturated hydraulic conductivity on horizontal distribution of soil moisture and in turn on water and energy balances within the basin(or a grid cell).By using the coupled models and SSiB model itself,the daily hydrological components such as runoffs are simulated and final results are analyzed carefully.Simulated daily results of hydrological components produced by both SSiB and coupled models show that(i) There is significant difference between results of soil wetness,its vertical distribution and seasonal variation,water and energy balance,and daily runoff in the basin predicted by SSiB and by the coupled models.The land surface model currently used such as SSiB is likely to misrepresent real feature of water and energy balances in the basin.(ii) Compared with the results for the basin predicted by SSiB,the coupled models predict more strong vertical and seasonal changes in soil wetness,higher evaporation and lower runoff,and improve the base flow simulation obviously.(iii) Comparing the results for the basin predicted by two coupled models with different integration approach and SSiB one by one,the results of daily runoffs and soil wetness predicted by the two coupled models are quite similar.It means,for the coupled models,the approach by dividing a region being considered into more subzones may have limited effects on improving runoff simulation results.The scheme only to divide the region into saturated and unsaturated zones may be a convenient and effective scheme.But then,if the results from the two coupled models for the basin are carefully compared,the simulated results by the coupled model with dividing the basin into more subzones will show higher evaporation and surface runoff but lower subsurface flow,lower total runoff,and lower ground water level averaged for five years.
基金supported by the Natural Science Foundation of Hunan Province (Grant No. 2020JJ4074)the Second Tibetan Plateau Scientific Expedition and Research Program (STEP) (Grant No. 2019QZKK0206)+2 种基金the Youth Innovation Promotion Association CAS (2021073)the National Key Scientific and Technological Infrastructure project “Earth System Science Numerical Simulator Facility” (EarthLab)the Huaihua University Double First-Class Initiative Applied Characteristic Discipline of Control Science and Engineering
文摘In order to compare the impacts of the choice of land surface model(LSM)parameterization schemes,meteorological forcing,and land surface parameters on land surface hydrological simulations,and explore to what extent the quality can be improved,a series of experiments with different LSMs,forcing datasets,and parameter datasets concerning soil texture and land cover were conducted.Six simulations are run for the Chinese mainland on 0.1°×0.1°grids from 1979 to 2008,and the simulated monthly soil moisture(SM),evapotranspiration(ET),and snow depth(SD)are then compared and assessed against observations.The results show that the meteorological forcing is the most important factor governing output.Beyond that,SM seems to be also very sensitive to soil texture information;SD is also very sensitive to snow parameterization scheme in the LSM.The Community Land Model version 4.5(CLM4.5),driven by newly developed observation-based regional meteorological forcing and land surface parameters(referred to as CMFD_CLM4.5_NEW),significantly improved the simulations in most cases over the Chinese mainland and its eight basins.It increased the correlation coefficient values from 0.46 to 0.54 for the SM modeling and from 0.54 to 0.67 for the SD simulations,and it decreased the root-mean-square error(RMSE)from 0.093 to 0.085 for the SM simulation and reduced the normalized RMSE from 1.277 to 0.201 for the SD simulations.This study indicates that the offline LSM simulation using a refined LSM driven by newly developed observation-based regional meteorological forcing and land surface parameters can better model reginal land surface hydrological processes.
基金support was provided by the National Basic Research Program of China (Project 2012CB956203)the Special Fund for Meteorological Research in the Public Interest (Grant No. GYHY201006023)+1 种基金the National Key Technologies R&D Program of China (Grant No. 2012BAC22B04)the National Natural Science Foundation of China (General Program, Grant No. 41105039)
文摘The authors examined the performance of version 3.4.1 of the Weather Research and Forecasting Model(WRF) with various land surface schemes in simulating a severe drought event in Southwest China. Five numerical experiments were completed using the Noah land surface scheme, the Pleim-Xiu land surface scheme, the Noah-MP land surface schemes, the Noah- MP scheme with dynamic vegetation, and the Noah-MP scheme with dynamic vegetation and groundwater processes. In general, all the simulations reasonably reproduced the spatial and temporal variations in precipitation, but significant bias was also found, especially for the spatial pattern of simulated precipitation. The WRF simulations with the Noah-MP series land surface schemes performed slightly better than the WRF simulation with the Noah and Pleim-Xiu land surface schemes in reproducing the severe drought events in Southwest China. The leaf area index(LAI) simulated by the different land surface schemes showed significant deviations in Southwest China. The Pleim-Xiu scheme overestimated the value of LAI by a factor of two. The Noah-MP scheme with dynamical vegetation overestimated the magnitude of the annual cycle of the LAI, although the annual mean LAI was close to observations. The simulated LAI showed a long-term lower value from autumn 2009 to spring 2010 relative to normal years. This indicates that the LAI is a potential indictor to monitor drought events.
文摘In this paper, the global and regional features of the seasonal variation of general circulation, and especially the Asian monsoon simulated by the Institute of Atmospheric Physics Two-level AGCM coupled with a sophisticated land-surface model (IAP94-GCM) are presented and compared with the observation. The comparison is made by using the equilibrium multiyear seasonal cycle climate from a 100-year integration. In the integration sea surface temperature (SST) and sea ice are taken from the observed climatological data (with seasonal variation) because our purpose is to see the improvement of simulation due to the coupling with an advanced land surface model. Overall, the IAP94-GCM provides a reasonably realistic simulation of the interseasonal and intraseasonal climatology of the Asian monsoon and yields an important information that sheds light on the thermal underpinning and the thermodynamics of the seasonal and even multiscale variabilities associated with the Asian summer monsoon.
文摘The Institute of Atmospheric Physics Land Surface Model (IAP94) has been incorporated into the IAP two-level atmospheric general circulation model (IAP GCM). Global and regional climatology averaged over the last 25 years of 100 year integrations from the IAP GCM with and without IAP94 (“bucket” scheme) is compared. The simulated results are also compared with the reanalysis data. Major findings are: \ \ (1) The IAP GCM simulation without IAP94 has extensive regions of warmer than observed surface air temperatures, while the simulation with IAP94 very much improves the surface air temperature. \ \ (2) The IAP GCM simulation with IAP94 gives improvement of the simulated precipitation pattern and intensity, especially the precipitation of East Asian summer monsoon and its intraseasonal migration of the rainbelts. \ \ (3) In five selected typical regions, for most of the surface variables such as surface air temperature, precipitation, precipitation minus evaporation, net radiation, latent heat flux and sensible heat flux, the IAP GCM with IAP94 provides better simulations.
基金National Basic Research Program of China (2012CB956203)State Key Program of National Natural Science of China (40830956)
文摘Two land surface models, Community Land Model (CLM3.5) and NOAH model, have been coupled to the Weather Research and Forecasting (WRF) model and been used to simulate the precipitation, temperature, and circulation fields, respectively, over eastern China in a typical flood year (1998). The purpose of this study is to reveal the effects of land surface changes on regional climate modeling. Comparisons of simulated results and observation data indicate that changes in land surface processes have significant impact on spatial and temporal distribution of precipitation and temperature patterns in eastern China. Coupling of the CLM3.5 to the WRF model (experiment WRF-C) substantially improves the simulation results over eastern China relative to an older version of WRF coupled to the NOAH-LSM (experiment WRF-N). It is found that the simulation of the spatial pattern of summer precipitation in WRF-C is better than in WRF-N. WRF-C also significantly reduces the summer positive bias of surface air temperature, and its simulated surface air temperature matches more closely to observations than WRF-N does, which is associated with lower sensible heat fluxes and higher latent heat fluxes in WRF-C.
基金Supported by the China Meteorological Administration Special Public Welfare Research Fund(GYHY201506002)National Key Research and Development Program of China(2018YFC1506601)+1 种基金National Natural Science Foundation of China(91437220)National Innovation Project for Meteorological Science and Technology(CMAGGTD003-5)。
文摘Land data assimilation(DA)is an effective method to provide high-quality spatially and temporally continuous soil moisture datasets that are crucial in weather,climate,hydrological,and agricultural research.However,most existing land DA applications have used remote sensing observations,and are based on one-dimensional(1 D)analysis,which cannot be directly employed to reasonably assimilate the recently expanded in-situ soil moisture observations in China.In this paper,a two-dimensional(2 D)localized ensemble-based optimum interpolation(En OI)scheme for assimilating in-situ soil moisture observations from over 2200 stations into land surface models(LSMs)is introduced.This scheme uses historical LSM simulations as ensemble samples to provide soil moisture background error covariance,allowing the in-situ observation information to be propagated to surrounding pixels.It is also computationally efficient because no additional ensemble simulations are needed.A set of ensemble sampling and localization length scale sensitivity experiments are performed.The En OI performs best for in-situ soil moisture fusion over China with an ensemble sampling of hourly soil moisture from the previous 7 days and a localization length scale of 100 km.Following the evaluation,simulations for in-situ soil moisture fusion are also performed from May 2016 to September 2016.The En OI analysis is notably better than that without in-situ observation fusion,as the wet bias of 0.02 m3 m-3 is removed,the root-mean-square error(RMSE)is reduced by about 37%,and the correlation coefficient is increased by about 25%.Independent evaluation shows that the En OI analysis performs considerably better than that without fusion in terms of bias,and marginally better in terms of RMSE and correlation.
基金Supported by"National Key Program for Developing Basic Sciences"G1999043400
文摘In this paper,the complex land surface model BATSle was coupled to the PSU/NCAR MMSV3.And the coupled model was used to simulate the heavy rain in summers of 1991 and 1998.The results show that,with the detailed land surface parameterization,the model can (1) simulate the distribution of heavy rain in Yangtze River Basin in summers of 1991 and 1998 more precisely,and improve the results by increasing the simulated precipitation rate;(2)improve the simulation results of surface temperature:(3)improve the simulation results of the circulation and temperature fields at middle and high levels.
基金The research reported herein was jointly supported by the National Natural Science Foundation of China under Grant Nos. 40145020, 40275023, 49794030, the National Key Program for Developing Basic Sciences under Grant Nos. G1998040905 and 2001CB309404,
文摘Surface runoff is mainly generated by two mechanisms, infiltration excess (Horton) runoff and saturation excess (Dunne) runoff; and the spatial variability of soil properties, antecedent soil moisture, topography, and rainfall will result in different surface runoff generation mechanisms. For a large area (e.g., a model grid size of a regional climate model or a general circulation model), these runoff generation mechanisms are commonly present at different portions of a grid cell simultaneously. Missing one of the two major runoff generation mechanisms and failing to consider spatial soil variability can result in significant under/over estimation of surface runoff which can directly introduce large errors in soil moisture states over each model grid cell. Therefore, proper modeling of surface runoff is essential to a reasonable representation of feedbacks in a land-atmosphere system. This paper presents a new surface runoff parameterization with the Philip infiltration formulation that dynamically represents both the Horton and Dunne runoff generation mechanisms within a model grid cell. The parameterization takes into account the effects of soil heterogeneity on Horton and Dunne runoff. The new parameterization is implemented into the current version of the hydrologically based Variable Infiltration Capacity (VIC) land surface model and tested over one watershed in Pennsylvania, USA and over the Shiguanhe Basin in the Huaihe Watershed in China. Results show that the new parameterization plays a very important role in partitioning the water budget between surface runoff and soil moisture in the atmosphere-land coupling system, and has potential applications on large hydrological simulations and land-atmospheric interactions. It is further found that the Horton runoff mechanism should be considered within the context of subgrid-scale spatial variability of soil properties and precipitation.
基金supported by the National Basic Research Program under Grant Nos.2010CB428403, 2010CB951001, and 2009CB421407the National Natural Science Foundation of China under Grant Nos. 41075062 and 40821092
文摘In this study, the Crop Estimation through Resource and Environment Synthesis model （CERES3.0） was coupled into the Biosphere-Atmosphere Transfer Scheme （BATS）, which is called BATS CERES, to represent interactions between the land surface and crop growth processes. The effects of crop growth and development on land surface processes were then studied based on numerical simulations using the land surface models. Six sensitivity experiments by BATS show that the land surface fluxes underwent substantial changes when the leaf area index was changed from 0 to 6 m2 m-2. Numerical experiments for Yucheng and Taoyuan stations reveal that the coupled model could capture not only the responses of crop growth and development to environmental conditions, but also the feedbacks to land surface processes. For quantitative evaluation of the effects of crop growth and development on surface fluxes in China, two numerical experiments were conducted over continental China： one by BATS CERES and one by the original BATS. Comparison of the two runs shows decreases of leaf area index and fractional vegetation cover when incorporating dynamic crops in land surface simulation, which lead to less canopy interception, vegetation transpiration, total evapotranspiration, top soil moisture, and more soil evaporation, surface runoff, and root zone soil moisture. These changes are accompanied by decreasing latent heat flux and increasing sensible heat flux in the cropland region. In addition, the comparison between the simulations and observations proved that incorporating the crop growth and development process into the land surface model could reduce the systematic biases of the simulated leaf area index and top soil moisture, hence improve the simulation of land surface fluxes.
基金supported by the National Program on Key Basic Research Project of China (Grant Nos.2010CB951604 and 2010CB950703)the National Natural Science Foundation of China General Program (Grant Nos.40975062 and 40875062)+2 种基金R&D Special Fund for Nonprofit Industry (Grant No.Meteorology GYHY201206008)the Key Technologies Research and Development Program of China (Grant No.2013BAC05B04)the Fundamental Research Funds for the Central Universities (Grant No.2012LYB42)
文摘As part of a joint effort to construct an atmospheric forcing dataset for China's Mainland with high spatiotemporal reso- lution, a new approach is proposed to construct gridded near-surface temperature, relative humidity, wind speed and surface pressure with a resolution of 1 km× 1 km. The approach comprises two steps： （1） fit a partial thin-plate smoothing spline with orography and reanalysis data as explanatory variables to ground-based observations for estimating a trend surface; （2） apply a simple kriging procedure to the residual for trend surface correction. The proposed approach is applied to observations collected at approximately 700 stations over China's Mainland. The generated forcing fields are compared with the corresponding components of the National Centers for Environmental Predic- tion （NCEP） Climate Forecast System Reanalysis dataset and the Princeton meteorological forcing dataset. The comparison shows that, both within the station network and within the resolutions of the two gridded datasets, the interpolation errors of the proposed approach are markedly smaller than the two gridded datasets.
