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1.
Snow cover fraction (SCF) has a significant influence on the surface albedo and thus on the radiation balance and surface
climate. Long-term three dimensional simulations with general circulation models (GCMs) show that the SCF greatly affects
the climate in the Northern Hemisphere. By means of both ground observations and remotely sensed data, several deficiencies
in the SCF simulated by the current ECHAM4 GCM were identified: over mountainous areas a substantial overestimation in the
SCF was found whereas flat areas showed a distinctly underestimated SCF. This work proposes a new parametrization of the SCF
for use in GCMs. Evaluations illustrate that it is beneficial to distinguish between the following three terrains: (1) flat,
non-forested areas, (2) mountainous regions and (3) forests. The modified SCF parametrization for flat, non-forested areas
was derived by using global datasets of ground-based snow depth and remote sensing observations of snow cover data. A 3-dimensional
ECHAM4 simulation showed that this modification raises the SCF by up to approximately 20%, mainly in areas with a relatively
thin snow cover. The comparison between remotely sensed and simulated mean monthly surface albedo revealed a significant overestimation
of the surface albedo in snow-covered mountainous areas. An extension of the current SCF parametrization in ECHAM4 to take
into account mountain effects, based on the French climate model Arpège, yielded a close agreement with satellite-derived
surface albedo. The adoption of the submodel for snow albedo, as used in the Canadian Land Surface Scheme (CLASS), combined
with a newly developed simple snow interception model, demonstrated the ability to capture the main physical processes of
snow-covered canopies, including the albedo. The validation of the new parametrization with Boreal Ecosystem-Atmosphere Study
(BOREAS) field data showed that the modification is appropriate to capture the main features of the albedo over snow-covered
forests during and after heavy snowfall events. Furthermore, the proposed modification has a beneficial impact on the delayed
snow melt in spring, a well-known problem in many current GCMs: The simulated surface albedo over the boreal forests decreases
by approximately 0.1 during winter and spring, which is in better agreement with ground-based observations. This induces a
significant rise in the surface temperature over extended parts of Eurasia and North America in late spring, which subsequently
yields a faster snowmelt and an accelerated retreat of the snow line.
Received: 28 April 2000 / Accepted: 18 December 2000 相似文献
2.
Benjamin I. Cook Gordon B. Bonan Samuel Levis Howard E. Epstein 《Climate Dynamics》2008,30(4):391-406
We investigate the response of a climate system model to two different methods for estimating snow cover fraction. In the
control case, snow cover fraction changes gradually with snow depth; in the alternative scenarios (one with prescribed vegetation
and one with dynamic vegetation), snow cover fraction initially increases with snow depth almost twice as fast as the control
method. In cases where the vegetation was fixed (prescribed), the choice of snow cover parameterization resulted in a limited
model response. Increased albedo associated with the high snow caused some moderate localized cooling (3–5°C), mostly at very
high latitudes (>70°N) and during the spring season. During the other seasons, however, the cooling was not very extensive.
With dynamic vegetation the change is much more dramatic. The initial increases in snow cover fraction with the new parameterization
lead to a large-scale southward retreat of boreal vegetation, widespread cooling, and persistent snow cover over much of the
boreal region during the boreal summer. Large cold anomalies of up to 15°C cover much of northern Eurasia and North America
and the cooling is geographically extensive in the northern hemisphere extratropics, especially during the spring and summer
seasons. This study demonstrates the potential for dynamic vegetation within climate models to be quite sensitive to modest
forcing. This highlights the importance of dynamic vegetation, both as an amplifier of feedbacks in the climate system and
as an essential consideration when implementing adjustments to existing model parameters and algorithms. 相似文献
3.
应用MODIS地表反照率产品MCD43C3,结合青藏高原自然带数据、积雪覆盖率和植被指数数据,采用一元线性回归方法分析了2000~2016年青藏高原地表反照率的分布及变化特征,结果表明:1）高原地表反照率空间分布差异大,整体上东南部低、西北部高,受地形和地表覆盖影响较大。2）高原地表反照率四季的空间分布变化明显,高海拔山脉和高寒灌丛草甸是高原地表反照率年内和年际变化的敏感地区。3）高原地表反照率年变化介于0.19~0.26,一定程度上表现为“双峰单谷”型,与地表覆盖类型的季节变化密切相关。4）高原地表反照率年际变化整体呈缓慢波动减小的趋势,平均变率约为－0.4×10-3 a-1,减小的区域约占高原总面积的66%,川西 —藏东针叶林带的西南部地区减小得最快,减小速率超过1.0×10-2 a-1。5）高原地表反照率减小与冰川消融和积雪减少密切相关,高原植被覆盖改善也是一个重要因素。 相似文献
4.
Snow-albedo feedback (SAF) is examined in 25 climate change simulations participating in the Coupled Model Intercomparison Project version 5 (CMIP5). SAF behavior is compared to the feedback’s behavior in the previous (CMIP3) generation of global models. SAF strength exhibits a fivefold spread across CMIP5 models, ranging from 0.03 to 0.16 W m?2 K?1 (ensemble-mean = 0.08 W m?2 K?1). This accounts for much of the spread in 21st century warming of Northern Hemisphere land masses, and is very similar to the spread found in CMIP3 models. As with the CMIP3 models, there is a high degree of correspondence between the magnitudes of seasonal cycle and climate change versions of the feedback. Here we also show that their geographical footprint is similar. The ensemble-mean SAF strength is close to an observed estimate of the real climate’s seasonal cycle feedback strength. SAF strength is strongly correlated with the climatological surface albedo when the ground is covered by snow. The inter-model variation in this quantity is surprisingly large, ranging from 0.39 to 0.75. Models with large surface albedo when these regions are snow-covered will also have a large surface albedo contrast between snow-covered and snow-free regions, and therefore a correspondingly large SAF. Widely-varying treatments of vegetation masking of snow-covered surfaces are probably responsible for the spread in surface albedo where snow occurs, and the persistent spread in SAF in global climate models. 相似文献
5.
Various proxy data reveal that in many regions of the Northern Hemisphere (NH), the middle Holocene (6 kyr BP) was warmer than the early Holocene (8 kyr BP) as well as the later Holocene, up to the end of the pre-industrial period (1800 AD). This pattern of warming and then cooling in the NH represents the response of the climate system to changes in orbital forcing, vegetation cover and the Laurentide Ice Sheet (LIS) during the Holocene. In an attempt to better understand these changes in the climate system, the McGill Paleoclimate Model (MPM) has been coupled to the dynamic global vegetation model known as VECODE (see Part I of this two-part paper), and a number of sensitivity experiments have been performed with the green MPM. The model results illustrate the following: (1) the orbital forcing together with the vegetation—albedo feedback result in the gradual cooling of global SAT from about 6 kyr BP to the end of the pre-industrial period; (2) the disappearance of the LIS over the period 8–6 kyr BP, associated with vegetation—albedo feedback, allows the global SAT to increase and reach its maximum at around 6 kyr BP; (3) the northern limit of the boreal forest moves northward during the period 8–6.4 kyr BP due to the LIS retreat; (4) during the period 6.4–0 kyr BP, the northern limit of the boreal forest moves southward about 120 km in response to the decreasing summer insolation in the NH; and (5) the desertification of northern Africa during the period 8–2.6 kyr BP is mainly explained by the decreasing summer monsoon precipitation. 相似文献
6.
R. J. Harding S.-E. Gryning S. Halldin C. R. Lloyd 《Theoretical and Applied Climatology》2001,70(1-4):5-18
Summary This paper summarises some of the key results from two European field programmes, WINTEX and LAPP, undertaken in the Boreal/Arctic
regions in 1996–98. Both programmes have illustrated the very important role that snow plays within these areas, not only
in the determination of energy, water and carbon fluxes in the winter, but also in controlling the length of the summer active
season, and hence the overall carbon budget. These studies make a considerable advance in our knowledge of the fluxes from
snow-covered landscape and the interactions between snow and vegetation. Also some of the first measurements of greenhouse
gas fluxes (carbon dioxide and methane) are reported for the European arctic and sub-arctic. The measurements show a considerable
variability across the arctic, with very high instantaneous values from sub-arctic birch and fen areas and extremely low fluxes
reported from the polar desert in the high arctic. The overall annual budgets are everywhere limited by the very short active
season in these regions. The heat flux over a high latitude boreal forest during late winter was found to be high. At low
solar angles the forest shades most of the snow surface, therefore an important part of the radiation never reaches the snow
surface but is absorbed by the forest. This indicates that in areas with sparse vegetation and low solar angles, absorption
of direct solar radiation is due to an apparent vegetation cover, which is much greater than the actual one.
The first steps are taken in using these measurements to improve models, both point soil/vegetation/atmosphere transfer schemes
and 3D meteorogical models. The results are encouraging; increasing the realism progressively improves the representation
of the fluxes. A start is made in developing landscape, or catchment scale models. There seems to be some hope that comparatively
simple relationships between evaporation and photosynthesis and leaf area may be sufficiently robust to allow the use of remotely
sensed images to investigate the areally averaged exchanges.
It is suspected that high latitude regions will experience considerable climatic and environmental change in the coming decades.
A well found prediction of how these regions will respond requires a comprehensive knowledge of how vegetation will respond
and how the changed vegetation will interact with the snow cover and the atmosphere. The studies from the LAPP and WINTEX
programmes presented in this volume are an important contribution to this understanding and provide a useful foundation for
future research.
Received March 6, 2001 相似文献
7.
L. D. Danny Harvey 《Climatic change》1988,13(2):191-224
A seasonal energy balance climate model containing a detailed treatment of surface and planetary albedo, and in which seasonally varying land snow and sea ice amounts are simulated in terms of a number of explicit physical processes, is used to investigate the role of high latitude ice, snow, and vegetation feedback processes. Feedback processes are quantified by computing changes in radiative forcing and feedback factors associated with individual processes. Global sea ice albedo feedback is 5–8 times stronger than global land snowcover albedo feedback for a 2% solar constant increase or decrease, with Southern Hemisphere cryosphere feedback being 2–5 times stronger than Northern Hemisphere cryosphere feedback.In the absence of changes in ice extent, changes in ice thickness in response to an increase in solar constant are associated with an increase in summer surface melting which is exactly balanced by increased basal winter freezing, and a reduction in the upward ocean-air flux in summer which is exactly balanced by an increased flux in winter, with no change in the annual mean ocean-air flux. Changes in the mean annual ocean-air heat flux require changes in mean annual ice extent, and are constrained to equal the change in meridional oceanic heat flux convergence in equilibrium. Feedback between ice extent and the meridional oceanic heat flux obtained by scaling the oceanic heat diffusion coefficient by the ice-free fraction regulates the feedback between ice extent and mean annual air-sea heat fluxes in polar regions, and has a modest effect on model-simulated high latitude temperature change.Accounting for the partial masking effect of vegetation on snow-covered land reduces the Northern Hemisphere mean temperature response to a 2% solar constant decrease or increase by 20% and 10%, respectively, even though the radiative forcing change caused by land snowcover changes is about 3 times larger in the absence of vegetational masking. Two parameterizations of the tundra fraction are tested: one based on mean annual land air temperature, and the other based on July land air temperature. The enhancement of the mean Northern Hemisphere temperature response to solar constant changes when the forest-tundra ecotone is allowed to shift with climate is only 1/3 to 1/2 that obtained by Otterman et al. (1984) when the mean annual parameterization is used here, and only 1/4 to 1/3 as large using the July parameterization.The parameterized temperature dependence of ice and snow albedo is found to enhance the global mean temperature response to a 2% solar constant increase by only 0.04 °C, in sharp contrast to the results of Washington and Meehl (1986) obtained with a mean annual model. However, there are significant differences in the method used here and in Washington and Meehl to estimate the importance of this feedback process. When their approach is used in a mean annual version of the present model, closer agreement to their results is obtained. 相似文献
8.
The effects of terrestrial ecosystems on the climate system have received most attention in the tropics, where extensive deforestation and burning has altered atmospheric chemistry and land surface climatology. In this paper we examine the biophysical and biogeochemical effects of boreal forest and tundra ecosystems on atmospheric processes. Boreal forests and tundra have an important role in the global budgets of atmospheric CO2 and CH4. However, these biogeochemical interactions are climatically important only at long temporal scales, when terrestrial vegetation undergoes large geographic redistribution in response to climate change. In contrast, by masking the high albedo of snow and through the partitioning of net radiation into sensible and latent heat, boreal forests have a significant impact on the seasonal and annual climatology of much of the Northern Hemisphere. Experiments with the LSX land surface model and the GENESIS climate model show that the boreal forest decreases land surface albedo in the winter, warms surface air temperatures at all times of the year, and increases latent heat flux and atmospheric moisture at all times of the year compared to simulations in which the boreal forest is replaced with bare ground or tundra. These effects are greatest in arctic and sub-arctic regions, but extend to the tropics. This paper shows that land-atmosphere interactions are especially important in arctic and sub-arctic regions, resulting in a coupled system in which the geographic distribution of vegetation affects climate and vice versa. This coupling is most important over long time periods, when changes in the abundance and distribution of boreal forest and tundra ecosystems in response to climatic change influence climate through their carbon storage, albedo, and hydrologic feedbacks. 相似文献
9.
Statistical and dynamical assessment of vegetation feedbacks on climate over the boreal forest 总被引：1，自引：1，他引：0
Vegetation feedbacks over Asiatic Russia are assessed through a combined statistical and dynamical approach in a fully coupled
atmosphere–ocean–land model, FOAM-LPJ. The dynamical assessment is comprised of initial value ensemble experiments in which
the forest cover fraction is initially reduced over Asiatic Russia, replaced by grass cover, and then the climatic response
is determined. The statistical feedback approach, adopted from previous studies of ocean–atmosphere interactions, is applied
to compute the feedback of forest cover on subsequent temperature and precipitation in the control simulation. Both methodologies
indicate a year-round positive feedback on temperature and precipitation, strongest in spring and moderately substantial in
summer. Reduced boreal forest cover enhances the surface albedo, leading to an extended snow season, lower air temperatures,
increased atmospheric stability, and enhanced low cloud cover. Changes in the hydrological cycle include diminished transpiration
and moisture recycling, supporting a reduction in precipitation. The close agreement in sign and magnitude between the statistical
and dynamical feedback assessments testifies to the reliability of the statistical approach. An additional statistical analysis
of monthly vegetation feedbacks over Asiatic Russia reveals a robust positive feedback on air temperature of similar quantitative
strength in two coupled models, FOAM-LPJ and CAM3–CLM3, and the observational record.
CCR Contribution # 931. 相似文献
10.
A new, physically-based snow hydrology has been implemented into the NCAR CCM1. The snow albedo is based on snow depth, solar zenith angle, snow cover pollutants, cloudiness, and a new parameter, the snow grain size. Snow grain size in turn depends on temperature and snow age. An improved expression is used for fractional snow cover which relates it to surface roughness and to snow depth. Each component of the new snow hydrology was implemented separately and then combined to make a new control run integrated for ten seasonal cycles. With the new snow hydrology, springtime snow melt occurs more rapidly, leading to a more reasonable late spring and summer distribution of snow cover. Little impact is seen on winter snow cover, since the new hydrology affects snow melt directly, but snowfall only indirectly, if at all. The influence of the variable grain size appears more important when snow packs are relatively deep while variable fractional snow cover becomes increasingly important as the snow pack thins. Variable surface roughness affects the snow cover fraction directly, but shows little effect on the seasonal cycle of the snow line. As an applicaion of the new snow hydrology, we have rerun simulations involving Antarctic and Northern Hemisphere glaciation; these simulations were previously made with CCM1 and the old snow hydrology. Relatively little difference is seen for Antarctica, but a profound difference occurs for the Northern Hemisphere. In particular, ice sheets computed using net snow accumulations from the GCM are more numerous and larger in extent with the new snow hydrology. The new snow hydrology leads to a better simulation of the seasonal cycle of snow cover, however, our primary goal in implementing it into the GCM is to improve the predictive capabilities of the model. Since the snow hydrology is based on fundamental physical processes, and has well-defined parameters, it should enable model simulations of climatic change in which we have increased confidence.This paper was presented at the Second International Conference on Modelling of Global Climate Variability, held in Hamburg 7–11 September 1992 under the auspices of the Max Planck Institute for Meteorology. Guest Editor for these papers is L. Dümenil 相似文献
11.
12.
Lee Wei-Liang Liou K. N. He Cenlin Liang Hsin-Chien Wang Tai-Chi Li Qinbin Liu Zhenxin Yue Qing 《Theoretical and Applied Climatology》2017,129(3-4):1373-1382
We investigate the snow albedo variation in spring over the southern Tibetan Plateau induced by the deposition of light-absorbing aerosols using remote sensing data from moderate resolution imaging spectroradiometer (MODIS) aboard Terra satellite during 2001–2012. We have selected pixels with 100 % snow cover for the entire period in March and April to avoid albedo contamination by other types of land surfaces. A model simulation using GEOS-Chem shows that aerosol optical depth (AOD) is a good indicator for black carbon and dust deposition on snow over the southern Tibetan Plateau. The monthly means of satellite-retrieved land surface temperature (LST) and AOD over 100 % snow-covered pixels during the 12 years are used in multiple linear regression analysis to derive the empirical relationship between snow albedo and these variables. Along with the LST effect, AOD is shown to be an important factor contributing to snow albedo reduction. We illustrate through statistical analysis that a 1-K increase in LST and a 0.1 increase in AOD indicate decreases in snow albedo by 0.75 and 2.1 % in the southern Tibetan Plateau, corresponding to local shortwave radiative forcing of 1.5 and 4.2 W m−2, respectively.
相似文献13.
A monthly snow accumulation and melt model is used with gridded monthly temperature and precipitation data for the Northern Hemisphere to generate time series of March snow-covered area (SCA) for the period 1905 through 2002. The time series of estimated SCA for March is verified by comparison with previously published time series of SCA for the Northern Hemisphere. The time series of estimated Northern Hemisphere March SCA shows a substantial decrease since about 1970, and this decrease corresponds to an increase in mean winter Northern Hemisphere temperature. The increase in winter temperature has caused a decrease in the fraction of precipitation that occurs as snow and an increase in snowmelt for some parts of the Northern Hemisphere, particularly the mid-latitudes, thus reducing snow packs and March SCA. In addition, the increase in winter temperature and the decreases in SCA appear to be associated with a contraction of the circumpolar vortex and a poleward movement of storm tracks, resulting in decreased precipitation (and snow) in the low- to mid-latitudes and an increase in precipitation (and snow) in high latitudes. If Northern Hemisphere winter temperatures continue to warm as they have since the 1970s, then March SCA will likely continue to decrease. 相似文献
14.
In this research, we studied the effects of black carbon (BC) aerosol radiative forcing on seasonal variation in the Northern Hemisphere (NH) using numerical simulations with the NASA finite-volume General Circulation Model (fvGCM) forced with monthly varying three-dimensional aerosol distributions from the Goddard Ozone Chemistry Aerosol Radiation and Transport Model (GOCART). The results show that atmospheric warming due to black carbon aerosols subsequently warm the atmosphere and land surfaces, especially those over Eurasia. As a result, the snow depth in Eurasia was greatly reduced in late winter and spring, and the reduction in snow cover decreased the surface albedo. Our surface energy balance analysis shows that the surface warming due to aerosol absorption causes early snow melting and further increases surface-atmosphere warming through snow/ice albedo feedback. Therefore, BC aerosol forcing may be an important factor affecting the snow/ice albedo in the NH. 相似文献
15.
To build land surface dataset for climate model,with application of remote sensing technique as well as the Geographic Information System(GIS),the data of surface type,roughness and albedo over China in 1997 were retrieved,resolutions being 10 km×10 km.Based on these data,an analysis is conducted on the geographic distributions and seasonal variations of surface vegetation cover and roughness as well as albedo over China.Results show that surface vegetation cover is mainly located to the south of Yangtze River,in Southwest and Northeast China andsparse vegetation cover is in the Northwest.The variation of land surface cover affects the variations of land surface roughness and albedo.High albedo occurred in the north of Xinjiang Autonomous Region,the north of Northeast China and the Qinghai-Xizang Plateau in winter,in correspondence with the location of snow cover.For most part of China,surface roughness decreases and albedo increases in winter,while the roughness increases and the albedo decreases in summer,which could mainly result from land surface cover(snow cover and vegetation cover)and soil moisture changes.This shows that the geographic distribution and seasonal variation of the albedo are almost opposite to those of the roughness,in agreement with theoretical results.Temporally,the amplitude of surface roughness change is quite small in comparison with the roughness itself. 相似文献
16.
The radiative forcing and climate response due to black carbon(BC) in snow and/or ice were investigated by integrating observed effects of BC on snow/ice albedo into an atmospheric general circulation model(BCC AGCM2.0.1) developed by the National Climate Center(NCC) of the China Meteorological Administration(CMA).The results show that the global annual mean surface radiative forcing due to BC in snow/ice is +0.042 W m 2,with maximum forcing found over the Tibetan Plateau and regional mean forcing exceeding +2.8 W m 2.The global annual mean surface temperature increased 0.071 C due to BC in snow/ice.Positive surface radiative forcing was clearly shown in winter and spring and increased the surface temperature of snow/ice in the Northern Hemisphere.The surface temperatures of snow-covered areas of Eurasia and North America in winter(spring) increased by 0.83 C(0.6 C) and 0.83 C(0.46 C),respectively.Snowmelt rates also increased greatly,leading to earlier snowmelt and peak runoff times.With the rise of surface temperatures in the Arctic,more water vapor could be released into the atmosphere,allowing easier cloud formation,which could lead to higher thermal emittance in the Arctic.However,the total cloud forcing could decrease due to increasing cloud cover,which will offset some of the positive feedback mechanism of the clouds. 相似文献
17.
The climatic impact of a Sonoran vegetation discontinuity 总被引：3，自引：0，他引：3
Robert C. Balling Jr. 《Climatic change》1988,13(1):99-109
The international fence separating Mexico and the United States is marked by a sharp vegetation discontinuity in the Sonoran Desert. Due to overgrazing, the Mexican side of the border has shorter grasses, more bare soil, and a higher albedo compared to the adjacent lands in the United States. In this investigation, long-term climate records are analyzed to determine the magnitude of any climatic differences associated with the spatial variation in the vegetation regime. The results suggest that summertime maximum temperatures recorded at the Mexican stations are significantly higher (by nearly 2.5 °C) than the Arizona stations when latitude and elevation are held constant. When only elevation is held constant, the difference in the maximum temperature jumps to approximately 4 dgC. No discernible changes in monthly and/or summer season precipitation could be identified in the records. These findings add support to other site-specific field measurements suggesting warming in desert areas where vegetation cover is decreasing and albedo is increasing. 相似文献
18.
春季欧亚大陆积雪对春夏季南北半球大气质量交换的可能影响 总被引：2，自引：0，他引：2
本文基于春季欧亚雪盖资料与大气再分析资料的奇异值分解(SVD)分析结果,结合数值试验,研究了春季欧亚大陆积雪变化与春、夏季南北半球大气质量交换的联系。研究表明,当春季欧亚积雪异常偏多时,同期欧亚大陆中高纬大范围地区的地面气温异常偏低,这种冷却效应可能持续至夏季,同时,冷空气的堆积造成了欧亚大陆地表气压(气柱大气质量)的增加,并且对应了夏季北半球大气总质量的异常上升,而南半球大气质量却明显下降。分析发现,春季欧亚积雪异常与夏季南北半球际大气质量涛动存在显著的滞后相关,而且前者还与同期及后期包括索马里急流和对流层上部80°E~120°E区域高空急流在内的多处越赤道气流变化联系密切。从数值模拟结果分析发现,以改变春季初始积雪状况作为驱动,欧亚大陆中高纬地区的低层大气环流出现了显著响应,即当积雪增加时,同期及其后夏季地面气温显著降低,并且冷异常区域对应着气柱质量的异常升高。 相似文献
19.
A full global atmosphere-ocean-land vegetation model is used to examine the coupled climate/vegetation changes in the extratropics
between modern and mid-Holocene (6,000 year BP) times and to assess the feedback of vegetation cover changes on the climate
response. The model produces a relatively realistic natural vegetation cover and a climate sensitivity comparable to that
realized in previous studies. The simulated mid-Holocene climate led to an expansion of boreal forest cover into polar tundra
areas (mainly due to increased summer/fall warmth) and an expansion of middle latitude grass cover (due to a combination of
enhanced temperature seasonality with cold winters and interior drying of the continents). The simulated poleward expansion
of boreal forest and middle latitude expansion of grass cover are consistent with previous modeling studies. The feedback
effect of expanding boreal forest in polar latitudes induced a significant spring warming and reduced snow cover that partially
countered the response produced by the orbitally induced changes in radiative forcing. The expansion of grass cover in middle
latitudes worked to reinforce the orbital forcing by contributing a spring cooling, enhanced snow cover, and a delayed soil
water input by snow melt. Locally, summer rains tended to increase (decrease) in areas with greatest tree cover increases
(decreases); however, for the broad-scale polar and middle latitude domains the climate responses produced by the changes
in vegetation are relatively much smaller in summer/fall than found in previous studies. This study highlights the need to
develop a more comprehensive strategy for investigating vegetation feedbacks. 相似文献
20.
植被覆盖异常变化影响陆面状况的数值模拟 总被引：15，自引：2，他引：15
利用NCAR最新的公用陆面模式CLM3．0，通过数值模拟初步研究了植被叶面积指数（LAI，leafareaindex）异常变化对陆面状况的可能影响，结果表明，植被LAI的异常变化能够引起地表能量平衡、地表水循环等陆面状况的异常。（1）植被LAI的异常变化主要影响太阳辐射在植被与地表之间的分配，以及地表的感热、潜热通量。植被LAI增大，能够引起植被吸收的太阳辐射增加，而到达土壤表面的太阳辐射减小，并导致植被的蒸发、蒸腾潜热通量增加，造成地表的蒸发潜热和感热通量不同程度的减小。（2）植被LAI增大时，植被对降水的拦截和植被叶面的蒸发增大，植被的蒸腾作用也明显增强；植被LAI增加会使得热带地区各个季节的土壤表面蒸发、地表径流减小，而土壤湿度有所增加；LAI增加造成中高纬度地区土壤蒸发的减少主要出现在夏季；LAI增加还能够引起中高纬地区冬、春积雪深度不同程度的增加，造成春末、夏初地表径流的增加。（3）植被LAI增加能够使得叶面和土壤温度有所下降，但植被LAI的变化对叶面、土壤温度的影响相对较小。 相似文献