陆面过程模式CoLM和NCAR_CLM3.0对中国典型森林生态系统陆气相互作用的模拟 I. 不同模式模拟结果的初步分析

CoLM(Common Land Model)和NCAR_CLM3.0(NCAR Community Lanol Model 3.0)是目前国际上广为应用的两个发展比较完善的陆面过程模式.本研究利用中国陆地生态系统通量观测研究网络(Chi-naFLUX)在长白山温带混交林和千烟洲亚热带人工针叶林观测站点的长期连续强化观测资料,对这两个模式在上述地区的模拟性能进行了初步评估.同观测资料的对比表明,两个模式均能较好地模拟出观测站点地表能量和水分平衡的基本特征,其中,CoLM对潜热通量的模拟性能更好.以对潜热通量为期1年的日均值的模拟为例,COLM和CLM3.0在长白山观测站模拟值和观测值时间序列的相关系数分别为0.80和0.65,在千烟洲站分别为0.69和0.64,均通过了0.01的信度检验;两个模式对全年平均的模拟与观测日平均值的比值在长白山分别为1.21和0.86,在千烟洲分别为0.83和0.60.研究结果表明,这两个陆面过程模式可以作为研究这两种典型森林生态系统陆气交换的基本工具.同时,对模式模拟性能差异的深入分析将有助于进一步改进陆面模式的参数化过程,为相关研究奠定更坚实的基础.     

基于FLUXNET数据集对陆面模式CoLM能量通量的单点评估

模式评估是模式发展中的重要一环。本文利用来自FLUXNET2015数据集的30个站点的涡动相关系统观测数据,重点关注能量通量,对通用陆面模式（Common Land Model version 2014,CoLM2014）在不同典型下垫面的模拟能力进行评估。结果表明,模式总体上能抓住感热、潜热和净辐射通量在日、季节和年平均等不同时间尺度上的变化特征,对感热、潜热和净辐射通量都有较好的模拟能力,净辐射的模拟效果最好,潜热通量次之。季节变化模拟中,感热、潜热通量在夏季不同植被型下站点的空间离散程度大于冬季,不同站点间模拟效果相差较大,净辐射多站点标准差变化幅度要小于感热、潜热,不同站点间模拟效果偏差较小。CoLM在常绿针叶林、稀树林地、草地、农田模拟感热、潜热通量的效果相对较好,在永久湿地、落叶阔叶林下模拟感热通量较差。本研究对CoLM2014在未来的改进和发展中提供了有用的参考。     

考虑碳氮水过程的动态根系方案在陆面模式SSiB4中的应用及效果评估

根系是植被重要组成部分,根系的动态变化可以通过调节根系吸水量改变土壤湿度,进而影响土壤蒸发等物理过程及植被蒸腾、光合作用等生化过程,最终改变生态系统物质循环和水热循环。本研究考虑土壤水分胁迫及土壤养分(氮)胁迫,模拟根系碳量在不同土壤层中的动态分配过程,用根系碳量比例表征根系的动态变化。基于SSiB4模式在亚马逊地区BRSa3站点、中国江西千烟洲CN-Qia站点进行单点模拟试验,研究动态根系方案对土壤湿度及陆气通量模拟结果的影响。结果表明:根系动态分布使更多深层土壤水分被吸收利用,改善了浅层土壤湿度的模拟效果,进而提高二氧化碳通量、感热及潜热通量的模拟精度。其中,BRSa3站点和CN-Qia站点浅层土壤湿度日平均的观测值与模拟值的相关系数分别提高了0.02和0.04,二氧化碳通量的相关系数分别提高了0.76和0.13,均通过99%显著性水平检验;改进了BRSa3站点干旱季和CN-Qia站点夏季碳吸收能力,二氧化碳通量的绝对偏差的改进幅度分别为33%和106%,二氧化碳通量日平均的观测值与模拟值的相关系数,分别提高了0.17和0.26,均通过99%显著性水平检验。总体而言,模拟时间段内各变量都更接近观测值,土壤湿度和二氧化碳通量的改进效果比感热通量和潜热通量的改进效果更加显著,土壤湿度通过土壤物理作用对感热通量和潜热通量的间接影响方式可能是造成差别的原因。各变量在BRSa3站点的改善更明显一些,不同植被覆盖类型的根系深度与结构可能是造成结果差别的主要原因。     

不同陆面过程模式对半干旱区通榆站模拟性能的检验与对比

随着全球气候变化和伴随而来的日益严重的干旱化问题,干旱/半干旱地区的陆气相互作用引起了越来越多的重视。利用国际协同强化观测期(CEOP)观测资料对3个不同的陆面过程模式BATS、LSM和CoLM在半干旱区通榆站进行了模拟检验与对比,考察了不同陆面过程模式对半干旱地区的模拟性能。结果表明,3个模式都可以较好地模拟出半干旱地区地气间的能量通量的季节和日变化,但模拟性能存在较大差异。对于地表温度和出射长波辐射的模拟,BATS表现最优;而对于感热和潜热通量的模拟,CoLM和LSM要好于BATS,其中CoLM的表现最好。各模式的模拟性能随着季节不同存在着很大的差异,夏季的模拟要好于冬季,3个模式都不能很好地模拟冬季该地区的潜热通量,说明对半干旱地区冬季地表过程的刻画还有待进一步提高。     

青藏高原地区不同下垫面陆面过程的数值模拟研究

利用陆面过程模式Common Land Model(CoLM),选取青藏高原上3个不同下垫面观测站(藏东南站、纳木错站和珠峰站)的观测资料,对这3个野外观测站进行了单点数值模拟试验。根据3个测站的试验数据,对模式中土壤孔隙度和饱和导水率进行了优化,针对青藏高原地区土壤层薄的特点,对模式中土壤分层方案进行了调整。结果表明,调整分层方案后的CoLM模式对3个测站土壤湿度的模拟性能较原分层方案有明显提高,平均偏差均减小0.014以上。但是与观测值相比,藏东南站土壤湿度的模拟整体偏低,纳木错站和珠峰站则整体偏高。对土壤温度而言,3个测站模拟与观测的相关系数都达到了0.9以上,珠峰站偏差较大,调整分层方案后模拟的偏差有一定的改进。模式较好地模拟了3个测站的净辐射、感热通量和潜热通量的日变化和季节变化情况,调整分层方案后潜热通量的改进最为明显。     

青藏高原西部冻融期陆面过程的模拟分析

利用CAMP/Tibet中CEOP-EOP3改则站2002年10月—2003年9月的观测资料作为强迫场,运用陆面过程模式CoLM(Common Land Model),对青藏高原西部陆面特征的模拟研究表明,在高原西部地表能量平衡过程中,冬半年,感热通量占主要地位,潜热通量较小;尤其在冻结期,潜热通量几乎等于零。但在高原西部的融冻期,潜热通量有显著变化。在干季向湿季转化时段的5月中下旬,表层土壤由于融冻而引起的频繁水分相变,使得潜热通量随之变化并开始增加,Bowen比由大变小。地表有效通量的变化与降水及土壤表层频繁的冻结—消融相联系。     

陆面过程模式CoLM和NCAR_CLM3.0对中国典型森林生态系统陆气相互作用的模拟Ⅰ.不同模式模拟结果的初步分析

量为期1年的日均值的模拟为例,COLM和CLM3.0在长白山观测站模拟值和观测值时间序列的相关系数分别为0.80和0.65,在千烟洲站分别为0.69和0.64,均通过了0.01的信度检验;两个模式对全年平均的模拟与观测日平均值的比值在长白山分别为1.21和0.86,在千烟洲分别为0.83和0.60.研究结果表明,这两个陆面过程模式可以作为研究这两种典型森林生态系统陆气交换的基本工具.同时,对模式模拟性能差异的深入分析将有助于进一步改进陆面模式的参数化过程,为相关研究奠定更坚实的基础.     

GLDAS资料驱动的Noah-MP陆面模式青藏高原地表能量交换模拟性能评估

使用Noah-MP陆面模式,在GLDAS数据的驱动下,对青藏高原不同区域6个观测站点的感热通量和潜热通量进行了模拟,并与实测值进行了对比分析。研究结果表明:使用默认参数化方案选项模拟的感热通量除在珠峰站冬春季偏高而夏秋季偏低以外,在其他站点均偏高;潜热通量的模拟在不同站点和不同季节存在较大差异,在藏东南站模拟结果较好,在珠峰站偏高,在慕士塔格站偏低,在纳木错站秋冬季偏低、在阿里站春季偏高、在那曲站夏季偏低。通过进一步分析模拟结果对各个参数化方案选项的敏感性,选出了更适合各站点感热通量及潜热通量模拟的参数化方案选项组合,提高了模式对各个站点全年整体模拟水平,使得模拟结果和站点观测相比具有更小的均方根误差和更高相关系数,但对一些站点部分季节的模拟可能会带来更大的误差。本研究为这些站点的陆面及耦合模式的模拟提供了参考,同时也能对青藏高原热源变化的模拟提供更准确的地气交换信息。     

稀疏植被地表反照率日变化对通量模拟效果的影响分析——以内蒙古荒漠草原感热和潜热通量为例

基于Noah陆面过程模式,利用内蒙古荒漠草原陆—气通量长期定位观测资料,模拟了地表反照率日变化对该荒漠草原感热和潜热通量的影响。结果表明,地表反照率的日变化将改善Noah陆面过程模式对内蒙古荒漠草原感热通量的模拟,但对受水分制约的潜热通量的改善效果不明显,表明准确地模拟地表反照率的日变化对模拟稀疏植被的感热通量至关重要。     

陆面过程模式TBLSHAW的设计及其在黄土高原地区的模拟研究

为了改善陆面过程模式在半干旱地区的模拟能力,在SHAW(Simultaneous Heat and Water Model)模式和CoLM(Common Land Surface Model)模式参数化方案基础上,结合黄土高原SACOL站(Semi-Arid Climate and Environment Observatory of Lanzhou University)得到的部分土壤和近地层的研究结果,利用SHAW模式的动力框架,发展了一个新的陆面过程模式TBLSHAW(Two-Big-Leaf-SHAW)。该模式由一层植被、多层土壤和湍流边界层构成。在植被层主要采取双大叶模型计算能量平衡;土壤层利用水热耦合传输模型计算土壤温度和湿度,并包含了冻融、蒸发及降水渗透等物理过程;湍流边界层采取莫宁—奥布霍夫理论计算湍流通量。最后利用SACOL站获取的观测资料,对TBLSHAW模式进行了模拟检验。结果表明,TBLSHAW模式能够合理地模拟半干旱地区各项陆面过程特征的变化趋势;模拟的土壤温度和土壤湿度与观测值的偏差较小,模式效率和相关系数较高;模拟的净短波辐射及向上长波辐射较好;但是模拟的感热通量、潜热通量与观测值偏差较大,这可能与该地区的能量闭合度较低有关,还有待进一步研究。     

森林火灾监测和森林火险天气等级

介绍了利用极轨气象卫星监测森林火灾的原理 ,分析了森林火险天气等级与森林火灾的对应关系     

Forest and Airport Wind Speeds

Abstract

A simple equation is developed for determining the ratio of wind speed above a rough vegetative canopy, such as a forest, to the wind speed over a relatively smooth surface, such as an airport, when both sites are subject to the same geostrophic wind. The usual assumptions for simplifying flow in the planetary boundary layer are followed and appropriate canopy parameters are introduced.

Values for the ratio of forest to airport wind speeds range from 0.4 to 0.7, with a typical value of 0.5.     

Potential Impact of Climatic Change on Tropical Rain Forest Seedlings and Forest Regeneration

Tropical rain forests are dynamic and continually regenerating by growth of seedlings up from the forest floor into canopy gaps that form on a cycle of usually a century of more in length. Changes in seedling establishment, survival, and release in gaps could thus change canopy species composition for a long time. Of likely climatic changes, evidence is presented that cyclone occurrence and increased rainfall seasonality could have important effects on seedling ecology. These forests and their species have lived through big Pleistocene and Holocene climatic changes, but today they are fragmented by human impact and so have less resilience to future climatic change. Management to accommodate climatic change should aim to reduce fragmentation and also canopy opening during logging operations. These are the same practices as advocated for biodiversity conservation. Tropical seasonal forests are also likely to be altered by expected climatic change, and also mainly at their regeneration stage.     

Carbon Sequestration and Turnover in Semiarid Savannas and Dry Forest

Data on carbon and biomass budgets under different land use in tropical savannas and some dry forests are reviewed. Global data show wide ranges of biomass carbon stocks (20-150 Mg C ha-1), net primary production (2-15 Mg C ha-1y-1) and litter production (2-10 Mg C ha-1y-1) for the semiarid tropics. Although ranges for soil carbon are also wide, an average figure for the top 20 cm is probably 10 g C kg-1, or about 25 Mg C ha-1. In order to arrive at a better understanding of C budgets and their controls, two regional reviews are presented for NE Brazil and W. Africa.In NE Brazil approximately 40% of the lands have "near-climax" native vegetation. Less than 10% of the area is planted annually, but about 3-4 times that area is affected by shifting cultivation which has an average cycle of 5 y arable use followed by 20 y or more recovery. Standing biomass of native caatinga shows nearly the full global range with 2-50 Mg C ha-1. Litter fall around 1-2 Mg C ha-1y-1 is partly decomposed and partly consumed by animals, resulting in low average soil C levels near 8 g kg-1, or 20 Mg C ha-1. Under cultivation, C sequestration is decreased, and soils lose approximately half their C stocks before being abandoned.In W. Africa between 50-70% of the land is under a management regime with minimal C returns to the soils. Overgrazing and over-exploitation for fuel wood has resulted in land degradation. Short fallow periods on cultivated lands have caused serious declines in soil C stocks. Both C sequestration and stocks are therefore lower in W. Africa than in NE Brazil.Improvements in the C sequestration in these semi arid regions depend on an increase in crop production under suitable rotations, improved fallow and animal husbandry, and a limitation on biomnass burning. Use of fertilizer is required for improved productivities but socioeconomic constraints largely prevent such improvements, resulting in a very limited scope for changes in soil C management.     

Canopy Architecture and Turbulence Structure in a Coniferous Forest

Synchronous sonic anemometric measurements at five heightswithin a mixed coniferous forest were used to test two different parameterisations ofcanopy architecture in the application of a second-order turbulence closure model. Inthe computation of the leaf drag area, the aerodynamic sheltering was replaced with anarchitectural sheltering, assumed to be analogous to the clumping index defined in radiativetransfer theory. Consequently, the ratio of leaf area density and sheltering factor was approximatedby the effective leaf area or the mean contact number, both obtained from the inversion of non-destructive optical measurements. The first parameter represents the equivalentrandomly dispersed leaf area in terms of shading, the second is the average number of leavesthat a straight line intercepts penetrating the canopy with a certain zenith angle. Theselection of this direction was determined by the analysis of the mean angle of the wind vectorduring sweep events. The drag coefficient values obtained from the inversion of themomentum flux equation, using the two proposed parameterisations, are in good agreement withvalues found in the literature. The predicted profiles of turbulence statistics reasonablymatch actual measurements, especially in the case of the mean contact numberparameterisation. The vertical profile of leaf drag area, obtained by forcing the turbulence modelto match the observed standard deviation of vertical velocity (_w), is intermediatebetween the two empirical ones. Finally, the proposed canopy parameterisations were appliedto a Lagrangian transport model to predict vertical profiles of air temperature, H₂O andCO₂ concentration.     

祁连山林区大气降水特征与森林对降水的截留作用

通过对连山寺大隆林区定位站1975－2000年的降水特征与森林对降水的再分配分析，建立了祁连山大隆林区降水与温度，降水与湿度，林冠截留的关系式。该区多年平均降水量为433.5mm，年变幅在326.4-539.7mm;降水量最大出现在夏季，占全年降水量的65．70％；海拔高度每升高100m，年了量平均递增4．55％，林区温度和湿度均与降水有较好的拟合关系。青海云杉林与祁连圆柏林林冠对大气降水的平均截留率分别为37．5％，31．7％，灌木林的截留率平均高达66．5％。青海云杉林林冠层平均截留率随着降雨量的增大逐渐减小，当降雨量为18.67mm时，林冠截留量达到最大，为14.72mm；青海云杉树干径流量占降水量的0．51％，当降雨量超过12.0mm时，才开始产生树干径流。青海云杉林枯枝落叶层对降雨的截留量随降雨量级增加而增大，截留率则随降雨量减小而增大，枯枝落叶层所具有的截留降雨和调蓄降雨作用使祁连山林区基本不发生地表径流。分析结果表明，祁连山林区对水源涵养和水流出山的时间调控有重要意义。     

Scaling Issues in Forest Succession Modelling

This paper reviews scaling issues in forest succession modelling, focusing on forest gap models. Two modes of scaling are distinguished: (1) implicit scaling, i.e. taking scale-dependent features into account while developing model equations, and (2) explicit scaling, i.e. using procedures that typically involve numerical simulation to scale up the response of a local model in space and/or time. Special attention is paid to spatial upscaling methods, and downscaling is covered with respect to deriving scenarios of climatic change to drive gap models in impact assessments. When examining the equations used to represent ecological processes in forest gap models, it becomes evident that implicit scaling is relevant, but has not always been fully taken into consideration. A categorization from the literature is used to distinguish four methods for explicit upscaling of ecological models in space: (1) Lumping, (2) Direct extrapolation, (3) Extrapolation by expected value, and (4) Explicit integration. Examples from gap model studies are used to elaborate the potential and limitations of these methods, showing that upscaling to areas as large as 3000 km² is possible, given that there are no significant disturbances such as fires or insect outbreaks at the landscape scale. Regarding temporal upscaling, we find that it is important to consider migrational lags, i.e. limited availability of propagules, if one wants to assess the transient behaviour of forests in a changing climate, specifically with respect to carbon storage and the associated feedbacks to the atmospheric CO₂ content. Regarding downscaling, the ecological effects of different climate scenarios for the year 2100 were compared at a range of sites in central Europe. The derivation of the scenarios is based on (1) imposing GCM grid-cell average changes of temperature and precipitation on the local weather records; (2) a qualitative downscaling technique applied by the IPCC for central and southern Europe; and (3) statistical downscaling relating large-scale circulation patterns to local weather records. Widely different forest compositions may be obtained depending on the local climate scenario, suggesting that the downscaling issue is quite important for assessments of the ecological impacts of climatic change on forests.     

Climate Change and People-Caused Forest Fire Occurrence in Ontario

Climate change that results from increasing levels of greenhouse gases in the atmosphere has the potential to increase temperature and alter rainfall patterns across the boreal forest region of Canada. Daily output from the Canadian Climate Centre coupled general circulation model (GCM) and the Hadley Centre's HadCM3 GCM provided simulated historic climate data and future climate scenarios for the forested area of the province of Ontario, Canada. These models project that in climates of increased greenhouse gases and aerosols, surface air temperatures will increase while seasonal precipitation amounts will remain relatively constant or increase slightly during the forest fire season. These projected changes in weather conditions are used to predict changes in the moisture content of forest fuel, which influences the incidence of people-caused forest fires. Poisson regression analysis methods are used to develop predictive models for the daily number of fires occurring in each of the ecoregions across the forest fire management region of Ontario. This people-caused fire prediction model, combined with GCM data, predicts the total number of people-caused fires in Ontario could increase by approximately 18% by 2020–2040 and50% by the end of the 21st century.     

Anomalies in Flux-Gradient Relationships Over Forest

Simultaneous profile and eddy correlation flux data gathered over Thetford Forest, U.K., have been analysed to find values of the vertical turbulent diffusivities K _M, K _H and K _E (for momentum, heat and water vapour transfer, respectively) at a reference height z _R, nine roughness lengths above the zero-plane displacement d. The results show: (i), that values of K _M over the forest are not significantly different from these predicted by semiempirical diabatic influence functions appropriate to much smoother surfaces such as short grass; and (ii), that K _H and K _E exceed their values predicted from the semiempirical functions by an average factor of 2 or more in unstable, near neutral and slightly stable conditions. These conclusions are strongly dependent on the assumed behaviour of d, here taken as 0.76 tree heights, independent of both property and stability. Consideration is given to an alternative analysis procedure, in which values of the zero-plane displacements d _H and d _E for heat and water vapour respectively, are obtained from the data by assuming K _H and K _E to be given by semiempirical diabatic influence functions; this procedure is shown to be unacceptable on both practical and physical grounds. To account for the anomalies in K _H and K _E, a mechanism is proposed in which the horizontally inhomogeneous temperature structure of the canopy causes free convection to be maintained by discrete; localized heat sources and/or sinks, effectively enhancing turbulent transport processes even in near neutral conditions.     

小兴安岭地区森林地被可燃物含水率变化规律及其与森林火险等级关系

通过对小兴安岭地区丰林自然保护区针阔叶混交林内的原始红松林地被物含水率与同期气象要素的比较分析,研究了森林地被可燃物含水率变化规律与森林火险等级关系.结果表明:森林地被可燃物含水率与降水量、蒸发能力、蒸发速度、空气温度、相对湿度、高温天气、风向和风速等气象要素密切相关;森林地被可燃物的含水率,特别是细小可燃物的含水率的高低与森林火险等级关系十分密切,地被可燃物含水率越高,森林火险等级越低.