陆面模式(SSiB)对敦煌荒漠戈壁下垫面陆面过程的模拟及敏感性试验

利用2000年5月26日至6月15日“敦煌试验”加强观测期的资料,对SSiB在中国西北典型干旱区荒漠戈壁下垫面上的使用性能进行了检验,并进行了植被覆盖变化的敏感性试验。模拟结果表明:在没有降水的情况下,SSiB在中国西北典型干旱区荒漠戈壁下垫面上具有一定的模拟能力。同时通过敏感性试验发现,模式对一些植被参数,如反照率、叶面积指数、粗糙度长度等相当敏感,因此要准确模拟陆面过程,必须保证这些参数的代表性。

陆面过程模式SSiB在中国西北典型干旱区使用性能的检验

利用2000年5月25日～6月15日敦煌试验加强期的观测资料,检验了SSiB模式在我国西北典型干旱区的使用性能.结果表明,在无降水强迫的情况下,模式对净辐射,感热,潜热和地表温度有较好的再现能力;但当加入降水强迫时,模式输出的模拟值与实测值有较大的差别,究其原因这可能与该模式对干旱区土壤水运动过程描述不准确有关.因此,要将此模式应用于典型干旱区,需要做进一步的改进工作.

陆面模式SSiB耦合TOPMODEL对流域水文模拟影响的数值试验

为了检验陆面模式SSiB耦合TOPMODEL模型对流域水量平衡模拟结果的影响,用原始SSiB与TOPMODEL按饱和区和非饱和区两种方案耦合的耦合模型(下称SSiBT)进行长江下游青弋江流域水文的数值试验,通过耦合模型与原始SSiB模式模拟结果的比较,并利用流域实测逐日流量和水量平衡资料,揭示了流域水文模拟结果对SSiB耦合TOPMODEL的响应和原因。结果表明:(1)与原始SSiB的模拟结果相比,SSiBT增加了土壤湿度的模拟结果和各层土壤湿度之间的差异,流域蒸散发增加而总径流减小。(2)原始SSiB不能准确地将径流在地表径流和基流之间分配,对于较小的土壤饱和导水率,原始SSiB产生过多的地表径流和洪峰流量;对于较大的土壤饱和导水率又产生过多的基流和明显偏小的洪峰流量。(3)即使土壤饱和导水率大到不会产生超渗产流,由于饱和区的存在,SSiBT在洪水期间也能产生足够大的地表径流,从而形成洪峰流量。由于考虑了地形引起的土壤湿度空间非均匀形成的饱和区产流,SSiBT改善了雨季逐日流量的模拟结果。

陆面过程对气候影响的数值模拟:SSiB与IAP/LASG L9R15 AGCM耦合及其模式性能

利用陆面过程模式 SSi B与 IAP/LASG发展的 L9R1 5AGCM的耦合 1 0 a积分试验 ,研究了全球尺度大气与地表的水分和能量交换以及陆地与大气环流和气候的相互作用。模拟表明 :SSi B模式可模拟出陆地上较为真实的表面通量及其日变化 ,较好地定量描述土壤 -植被 -大气连续体系 ( SPAC)中能量和水分的传输过程。因此 ,将其引入气候模式中能够模拟出比 CTL- AGCM更合理的气候平均状态、水汽分布以及水汽输送的气候特征 ,特别是亚洲夏季风水汽输送独特的地域性 ,再现了大气环流 ,尤其是陆面气候的基本特征。并指出 ,陆面过程参数化的引进及其陆面状况的变化显著地改善了全球陆地上的水分平衡状况。利用改进的再循环降水模式 ,进一步研究了陆面过程参数化明显改进降水模拟的物理机制。指出全球陆地 ,特别是盛夏北半球干旱、半干旱地区的再循环降水率明显减小 ,与陆面上表面潜热通量的显著减小区一致 ,从而克服了许多未耦合陆面过程的 AGCMs因对地表水过程非常简单地参数化导致的普遍存在着整个陆地降水偏高 ,改善了全球陆地上的水分平衡状况。因此 ,在充分耦合的陆气环流模式中模拟的降水分布与实况接近。

Validation of SSiB Model over Grassland with CHeRES Field Experiment Data in 2001

The Simplified Simple Biosphere model (SSiB) is validated in off-line simulations against field measurements in the summer of 2001 from the China Heavy Rainfall Experiment and Study (CHeRES) over a grassland site located in the lower reaches of the Yangtze River. When initialized and driven by the observed atmospheric forcing, the model reproduced the observed surface heat fluxes and surface skin temperature realistically. The model was also able to well simulate the variation of soil water content. The sensitivity experiments found that the leaf reflectance was the most significant parameter in improving the estimation of surface albedo during both wet and dry periods. This study suggests that the model is capable of simulating the physical processes and of assessing the impact of biophysical parameters that relate to land-atmosphere interactions over the eastern Asian monsoon regions, which is crucial for mesoscale atmospheric models.

Effects of Dynamic Vegetation on Global Climate Simulation Using the NCEP GFS and SSiB4/TRIFFID

Two global experiments were carried out to investigate the effects of dynamic vegetation processes on numerical climate simulations from 1948 to 2008.The NCEP Global Forecast System(GFS)was coupled with a biophysical model,the Simplified Simple Biosphere Model(SSi B)version 2(GFS/SSi B2),and it was also coupled with a biophysical and dynamic vegetation model,SSi B version 4/Top-down Representation of Interactive Foliage and Flora Including Dynamics(TRIFFID)(GFS/SSi B4/TRIFFID).The effects of dynamic vegetation processes on the simulation of precipitation,near-surface temperature,and the surface energy budget were identified on monthly and annual scales by assessing the GFS/SSi B4/TRIFFID and GFS/SSi B2 results against the satellite-derived leaf area index(LAI)and albedo and the observed land surface temperature and precipitation.The results show that compared with the GFS/SSiB2 model,the temporal correlation coefficients between the globally averaged monthly simulated LAI and the Global Inventory Monitoring and Modeling System(GIMMS)/Global Land Surface Satellite(GLASS)LAI in the GFS/SSi B4/TRIFFID simulation increased from 0.31/0.29(SSiB2)to 0.47/0.46(SSiB4).The correlation coefficients between the simulated and observed monthly mean near-surface air temperature increased from 0.50(Africa),0.35(Southeast Asia),and 0.39(South America)to 0.56,0.41,and 0.44,respectively.The correlation coefficients between the simulated and observed monthly mean precipitation increased from 0.19(Africa),0.22(South Asia),and 0.22(East Asia)to 0.25,0.27,and 0.28,respectively.The greatest improvement occurred over arid and semiarid areas.The spatiotemporal variability and changes in vegetation and ground surface albedo modeled by the GFS with a dynamic vegetation model were more consistent with the observations.The dynamic vegetation processes contributed to the surface energy and water balance and in turn,improved the annual variations in the simulated regional temperature and precipitation.The dynamic vegetation processes had the greatest influence on the spatiotemporal changes in the latent heat flux.This study shows that dynamic vegetation processes in earth system models significantly improve simulations of the climate mean status.

NUMERICAL SIMULATIONS OF EFFECTS OF LAND SURFACE PROCESSES ON CLIMATE——IMPLEMENTING OF SSiB IN IAP/LASG AGCM AND ITS PERFORMANCE

This is an investigation of exchanges of energy and water between the atmosphere and the vegetated continents,and the impact of and mechanisms for land surface-atmosphere interactions on hydrological cycle and general circulation by implementing the Simplified Simple Biosphere (SSiB)model in a modified version of IAP/LASG global spectral general model(L9R15 AGCM). This study reveals that the SSiB model produces a better partitioning of the land surface heat and moisture fluxes and its diurnal variations,and also gives the transport of energy and water among atmosphere,vegetation and soil explicitly and realistically.Thus the coupled SSiB-AGCM runs lead to the more conspicuous improvement in the simulated circulation,precipitation,mean water vapor content and its transport.particularly in the Asian monsoon region in the real world than CTL-AGCM runs.It is also pointed out that both the implementation of land surface parameterizations and the variations in land surface into the GOALS model have greatly improved hydrological balance over continents and have a significant impact on the simulated climate. particularly over the massive continents. Improved precipitation recycling model was employed to verify the mechanisms for land surface hydrology parameterizations on hydrological cycle and precipitation climatology in AGCM. It can be argued that the recycling precipitation rate is significantly reduced,particularly in the arid and semi-arid region of the boreal summer hemisphere,coincident with remarkable reduction in evapotranspiration over the continental area.Therefore the coupled SSiB-AGCM runs reduce the bias of too much precipitation over land surface in most AGCMs,thereby bringing the simulated precipitation closer to observations in many continental regions of the world than CTL-AGCM runs.

流域植被与土壤导水系数对青弋江流域水文影响的数值试验

为了揭示植被覆盖以及土壤导水系数变化对流域水文的影响,用陆面模式SSiB4与动态植被模型TRIFFID和流域地形指数水文模型TOPMODEL的耦合模型(SSiBT/TRIFFID)进行流域植被覆盖与土壤导水系数变化对流域水文影响的数值试验。结果表明:①植被类型明显影响流域地表能量平衡和水量平衡;②流域森林植被能明显减小一般洪峰流量,但对大的洪峰流量没有减弱作用;③减小土壤导水系数将明显增加地表径流和减小基流。

我国6 kaBP植被变化的气候模拟研究(英文)

根据花粉恢复的古植被表明中国森林区的常绿阔叶林、落叶阔叶林以及针叶林在6 ka BP向北扩张,反映了6ka BP夏季和冬季均比现代温暖的气候特征。然而,根据地球轨道参数变化驱动的气候模式,由于6kaBP时北半球夏季太阳辐射高于现代,而冬季太阳辐射低于现代,模拟的6ka BP夏季温度比现代温暖,但冬季比现代寒冷。模拟得出的冬季寒冷与地质资料显示的冬季增温不一致,说明6 ka BP的气候和植被变化并不完全受到太阳辐射变化的控制。针对这一重大缺陷,我们利用具有陆面过程的全球大气环流模式(AGCM+SsiB),采用了外动力太阳辐射变化和古地表状况的强迫边界场进行了古气候模拟试验。模拟结果能够捕捉到亚洲季风地区6 kaBP冬季气候变暖的气候特征,初步阐明6 ka BP植被变化的气候动力学机制。

一个耦合了简化生物圈方案的全球大气环流谱模式及其性能测试

在美国ＮＭＣＡＧＣＭ模式的基础上，参照ＣＯＬＡ低分辨率ＡＧＣＭ模式，移植和改进了一个包括植被层陆面过程的陆－气耦合全球大气环流谱模式（Ｒ１５Ｌ９）。其水平分辨率为菱形截断１５波，垂直方向分为９层，陆面过程采用简化的简单生物圈模式（ＳＳｉＢ）。该模式改善了对陆面特征的刻画。通过进一步完善初值处理、下垫面边值处理、模式后诊断及图形处理，使其成为一套可用于气候模拟研究的工具。对１月、７月平均场的模拟及其与１月、７月气候平均场的比较表明，该模式的性能良好。

Improving Simulations of Vegetation Dynamics over the Tibetan Plateau:Role of Atmospheric Forcing Data and Spatial Resolution

The efficacy of vegetation dynamics simulations in offline land surface models(LSMs)largely depends on the quality and spatial resolution of meteorological forcing data.In this study,the Princeton Global Meteorological Forcing Data(PMFD)and the high spatial resolution and upscaled China Meteorological Forcing Data(CMFD)were used to drive the Simplified Simple Biosphere model version 4/Top-down Representation of Interactive Foliage and Flora Including Dynamics(SSiB4/TRIFFID)and investigate how meteorological forcing datasets with different spatial resolutions affect simulations over the Tibetan Plateau(TP),a region with complex topography and sparse observations.By comparing the monthly Leaf Area Index(LAI)and Gross Primary Production(GPP)against observations,we found that SSiB4/TRIFFID driven by upscaled CMFD improved the performance in simulating the spatial distributions of LAI and GPP over the TP,reducing RMSEs by 24.3%and 20.5%,respectively.The multi-year averaged GPP decreased from 364.68 gC m^(-2)yr^(-1)to 241.21 gC m^(-2)yr^(-1)with the percentage bias dropping from 50.2%to-1.7%.When using the high spatial resolution CMFD,the RMSEs of the spatial distributions of LAI and GPP simulations were further reduced by 7.5%and 9.5%,respectively.This study highlights the importance of more realistic and high-resolution forcing data in simulating vegetation growth and carbon exchange between the atmosphere and biosphere over the TP.

Implementing a New Snow Scheme in Simplified Simple Biosphere Model

This paper describes a modified version of SSIB through implementing a new snow model (SAST) in Simplified Simple Biosphere Model SSIB for climate study and presents the evaluation results by testing the scheme based on the field data from Russia and France. The relevant equations in the scheme are given, which describe complicated interactive processes among air-vegetation-snow-soil continuum through mass and heat exchange. An efficient numerical scheme is developed to solve the nonlinear equations successfully. By using the field data from Russia and France, the function of the new scheme is evaluated. The numerical results from the scheme show good agreement with field data. It indicates that the scheme developed here is workable and can be extended for climate study. Key words Snow cover model (SAST) - SSIB - Implementing - Evaluation This work was supported by the foundation from China: 1)NSF Grant 49835010, 2) National key program G1998040900—Part 1, 3) NSF 40075019, 4) NSF 49823002.

Numerical simulation of the effects of global warming on vegetation in Asia

The response of vegetation to global warming is closely related to human living environment,and uncertainty in understanding the response remains.This study aims to investigate the effects of CO_(2),temperature and precipitation changes under global warming on natural vegetation in Asia.The biophysical/dynamic vegetation model SSiB4/TRIFFID was employed to perform numerical experiments under different climate scenarios for Asia using the Princeton global forcing dataset(1948–2006).The results showed that precipitation and CO_(2) were the key factors for vegetation growth.The effect of temperature on natural vegetation varied among the study regions.Generally,an increase in temperature was conducive to vegetation growth in eastern Asia,but not in the arid and semi-arid areas of western Asia.In arid and semi-arid areas or in the vicinity of desert,the forcing effects of temperature,precipitation and CO_(2) were more remarkable,which led to a noticeable change in the area of bare land.In terms of the distribution of vegetation species,the above forcing had a greater impact on shrubs,C3 grasses and C4 plants,but less of an impact on broadleaf and coniferous forest.It was also found that,although there was a notable positive correlation between precipitation and vegetation leaf area index in northern high latitudes,the vegetation cover did not increase with precipitation,which was countered by the negative effect of surface cooling in summer.