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1.
植被总初级生产力(Gross Primary Productivity,GPP)决定进入陆地生态系统的初始物质和能量,是陆地碳循环与大气碳库的重要联系纽带。利用陆面过程模式CLM4-CN(Community Land Model version 4 with CarbonNitrogen interactions)模拟和分析中国区域1982~2004年GPP(CLM4_GPP)时空变化特征,并通过与基于观测数据升尺度所得到的MTE_GPP(Model Tree Ensemble,MTE)进行比较,评估CLM4在中国区域GPP的模拟能力,同时探讨了不同土地覆盖资料对GPP的影响。结果表明:(1)CLM4-CN能够较好地刻画中国区域GPP空间分布格局,表现为由东南向西北递减,但在量值上大部分区域尤其是30°N以南地区存在高估,CLM4-CN模拟的GPP多年平均值为13.7 Pg C a-1,而MTE_GPP仅为6.9 Pg C a-1;(2)CLM4-CN可以合理模拟GPP的季节变化(与MTE_GPP相关系数大于0.9),在量值上对温带阔叶落叶林、寒带阔叶落叶林、寒带阔叶落叶灌木、C3极地草地、C3非极地草地和农作物模拟较好(均方根偏差RMSD100 g C m-2 month-1);(3)不同植物功能型CLM4_GPP表现出的年际变率均大于MTE_GPP,仅热带针叶常绿林、寒带阔叶落叶林和C3极地草地的CLM4_GPP与MTE_GPP变化趋势一致;(4)降水是研究时段内控制整个中国区域GPP的主要气候因子,但不同地区存在较大差异;(5)两种不同土地覆盖资料GPP模拟结果的显著差异表明,精确的土地覆盖是准确模拟GPP的重要基础。  相似文献   

2.
The maximum rate of carboxylation(Vcmax) is a key photosynthetic parameter for gross primary production(GPP) estimation in terrestrial biosphere models. A set of observation-based Vcmax values, which take the nitrogen limitation on photosynthetic rates into consideration, are used in version 4.5 of the Community Land Model(CLM4.5). However, CLM4.5 with carbon-nitrogen(CN) biogeochemistry(CLM4.5-CN) still uses an independent decay coefficient for nitrogen after the photosynthesis calculation. This means that the nitrogen limitation on the carbon cycle is accounted for twice when CN biogeochemistry is active. Therefore, to avoid this double nitrogen down-regulation in CLM4.5-CN, the original Vcmax scheme is revised with a new one that only accounts for the transition between Vcmax and its potential value(without nitrogen limitation). Compared to flux towerbased observations, the new Vcmax scheme reduces the root-mean-square error(RMSE) in GPP for mainland China by 13.7 g C m-2 yr-1, with a larger decrease over humid areas(39.2 g C m-2 yr-1). Moreover, net primary production and leaf area index are also improved, with reductions in RMSE by 0.8% and 11.5%, respectively.  相似文献   

3.
杜娟  刘朝顺  高炜 《气象科学》2016,36(2):184-193
以通用陆面模式CLM 3.0(Community Land Model 3.0)为模型算子,基于集合卡尔曼滤波(Ensemble Kalman Filter,En KF)发展了一个土壤温湿度同化系统,主要用于改进模式对土壤温湿度和地表水热通量的模拟精度,并考察集合样本数、同化频率及不同观测量的组合对同化效果的影响。该系统同化了FLUXNET两个站点(阿柔和Bondville)不同土壤深度、不同时间频率的土壤温度和湿度数据。通过对阿柔站不同集合样本数的设计,综合考虑计算成本和计算精度,最终将集合样本数设置为40。通过分析三种同化方案对同化频率的敏感性得出,同化土壤温度最为敏感,同时同化土壤温湿度次之,同化土壤湿度最不敏感。对于阿柔站点,同化系统对不同土壤深度温度和湿度的模拟精度均能提高90%,潜热通量的均方根误差由94.0 W·m~(-2)降为46.3 W·m~(-2),感热通量均方根误差由55.9 W·m~(-2)降为24.6 W·m~(-2)。Bondville站点浅层土壤温度的改进在30%左右,深层土壤温度改进达到60%,对土壤湿度的改进均在70%以上,潜热通量和感热通量的均方根误差分别从57.4 W·m~(-2)和54.4 W·m~(-2)降为51.0 W·m~(-2)和42.5 W·m~(-2)。试验结果表明,同化站点土壤温湿度数据对土壤水热状况及通量的模拟改进非常有效,同时也验证了同化土壤水分遥感产品的可行性和必要性。  相似文献   

4.
Observations have shown a largely enhanced seasonal amplitude of northern atmospheric CO2 in the past several decades, and this enhancement is attributable to the increased seasonal amplitude of northern net ecosystem productivity (NEP amplitude). In the future, however, the changes in NEP amplitude are not clear, because of the uncertainties in climate change and vegetation dynamics. This study investigated the changes in NEP amplitude north of 45°N under future global warming by using a dynamic global vegetation model (DGVM). The authors conducted two sets of simulations: a present-day simulation (1981–2000) and future simulations (2081–2100) forced by RCP8.5 outputs from CMIP5. The results showed an overall enhanced northern NEP amplitude under the RCP8.5 scenario because of the increased maximum NEP and the decreased minimum NEP. The increases (decreases) in the maximum (minimum) NEP resulted from stronger (weaker) positive changes in gross primary production (GPP) than ecosystem respiration (ER). Changes in GPP and ER are both dominantly driven by surface air temperature and vegetation dynamics. This work highlights the key role of vegetation dynamics in regulating the northern terrestrial carbon cycle and the importance of including a DGVM in Earth system models.摘要观测显示过去几十年北半球大气二氧化碳季节幅度大幅增加, 这主要是由北半球陆地净生态系统生产力季节幅度的增加所致. 但是, 因为气候变化和植被动态的不确定性, 未来陆地净生态系统生产力季节幅度的变化还很不清楚. 本工作利用全球植被动力学模式研究了全球变暖背景下北纬45°以北陆地净生态系统生产力季节幅度的变化. 作者做了两大类试验: 当代试验 (1981−2000) 和CMIP5 RCP8.5 变暖情景驱动的未来试验 (2081−2100) . 结果显示, 在RCP8.5变暖情景下北半球中高纬陆地净生态系统生产力季节幅度整体增加, 这是因为陆地净生态系统生产力的月最大值增加且月最小值减小. 最大 (最小) 陆地净生态系统生产力的增加 (减小) 是由于总初级生产力的增加强 (弱) 于生态系统总呼吸. 总初级生产力和生态系统总呼吸的变化都主要受地表气温和植被动态的驱动. 本工作强调了植被动态对北半球中高纬陆地生态系统碳循环的关键调制作用, 也强调了在地球系统模式中包含全球植被动力学模式的重要性.  相似文献   

5.
不同陆面模式对我国地表温度模拟的适用性评估   总被引：1，自引：0，他引：1       下载免费PDF全文
基于CLDAS大气驱动数据驱动CLM3.5陆面模式和3种不同参数化方案下的Noah-MP陆面模式模拟得到的地表温度,利用中国气象局2009-2013年2000多个国家级地面观测站地表温度进行质量评估。结果表明:从时间分布看,模拟地表温度与观测的偏差及均方根误差均呈季节性波动;从空间分布看,模拟地表温度与观测的偏差及均方根误差在中国东部地区相对于中国西部地区更小。选择Noah-MP陆面模式3种不同参数化方案模拟结果进行对比,结果表明:Noah-MP模式的非动态植被方案不变时,考虑植被覆盖度的二流近似辐射传输方案的Noah-MP陆面模式模拟的地表温度优于考虑太阳高度角和植被三维结构的二流近似辐射传输方案Noah-MP陆面模式模拟的地表温度;选择动态植被方案的Noah-MP陆面模式模拟的地表温度优于选择非动态植被方案的Noah-MP陆面模式;总体而言,考虑动态植被方案的Noah-MP陆面模式模拟的地表温度优于其他两种参数化方案的Noah-MP陆面模式以及CLM3.5陆面模式模拟的地表温度。  相似文献   

6.
利用一套高分辨率的气候驱动场和全球动态植被模型LPJ-WHyMe(Lund-Potsdam-Jena-Wetland Hydrology and Methane),模拟了中国东北地区潜在植被分布,并对中国东北地区1997～2010年平均净初级生产力（Net Primary Production, NPP）、净生态系统生产力（Net Ecosystem Production, NEP）、燃烧面积、火灾碳排放、土壤温度和土壤湿度进行了估算。LPJ-WHyMe的特点在于能够描述冻融的物理过程以及土壤中多层的湿度和温度。数值结果表明,在LPJ-WHyMe模型提供的植被功能类型（Plant Function Type, PFT）划分的条件下,中国东北地区主要分布了5种植被功能类型,即温带夏绿阔叶林带、北方常绿针叶林带、北方夏绿针叶林带、北方夏绿阔叶林带和温带草本植物。在研究时间段内,中国东北地区NPP的年平均值为376 g(C) m-2,变化范围在324.15～424.86 g(C) m-2之间。火灾机制的引入使得LPJ-WHyMe模型对NEP的模拟能力进一步提高,即NEP年平均值为42.36 g(C) m-2,表明中国东北地区陆地生态系统总体表现为“碳汇”。中国东北地区年平均燃烧面积分数为0.84%,火灾碳排放量为42.41 g(C) m-2,整体上模型高估了燃烧面积值和火灾碳排放量,模型对东北地区火灾的模拟仍然存在一定的局限性。中国东北地区土壤温度与气温呈正相关关系,且各层土壤温度与气温的相关性随着深度的增加而减弱。中国东北地区土壤湿度与降水呈正相关关系,土壤湿度与气温呈反相关关系。上述结果表明LPJ-WHyMe模型模拟中国东北地区潜在植被分布和碳循环是有效的。  相似文献   

7.
In this study, variations in carbon dioxide (CO2) fluxes resulting from gross primary production (GPP), net ecosystem exchange (NEE), and respiration (R e) of soybean (Glycine max L.) were investigated by the Eddy Covariance method during the growing period from June to November 2005 on an irrigated sand field at the Arid Land Research Center, Tottori University in Tottori, Japan. Although climatic conditions were humid and temperate, the soybeans required frequent irrigation because of the low water holding capacity of the sandy soil at the field site. Finally, it has been found that the accumulated NEE, GPP, and R e fluxes of soybean over 126 days amount to ?93, 319, and 226 gC m?2, respectively. Furthermore, the average ratio of GPP to R e was 1.4 and the average ratio of NEE to GPP was about ?0.29 for the growth period of soybean. Daily maximum NEE of ?3.8 gC m?2 occurred when LAI was 1.1.  相似文献   

8.
气溶胶质量密度是气溶胶重要的参数,它影响着大气中复杂的化学反应,也与气溶胶的传输过程和空间分布息息相关.基于MERRA-2再分析资料提供的气溶胶柱质量密度数据,研究了我国塔里木盆地1980—2018年长时间序列的沙尘气溶胶柱质量密度的时空分布特征.结果表明,沙尘气溶胶和沙尘PM2.5气溶胶柱质量密度有很大的变化范围,平均值分别为0.33和0.086 g/m2,同时具有明显的年际、月和季节变化特征.沙尘气溶胶和沙尘PM2.5气溶胶柱质量密度的年平均值在0.24~0.41和0.06~0.11 g/m2范围内变化;春季最大,其平均值分别为0.47和0.12 g/m2,冬季最小,其平均值分别为0.13和0.04 g/m2;月平均值最大出现在5月,分别为0.57和0.14 g/m2,最小在1月,分别为0.1和0.03 g/m2.  相似文献   

9.
ABSTRACT

This study was carried out to quantify the physical processes of lakes in the Tibetan Plateau using the Community Land Model, version 4.5 (CLM4.5), coupled with a physically based, 10-layer lake model developed by the National Center for Atmospheric Research. The CLM was forced with 10?km resolution reanalysis data to attempt to understand detailed lake processes and how these processes affect lake surface temperature. In this study, we simulated seasonal and interannual variations of lake surface temperature for Lake Qinghai, Zhaling Co, and Nam Co in the Tibetan Plateau and compared these simulations with observations. The results showed that the CLM4.5 lake model simulations reproduced the observed lake surface temperatures for Lake Qinghai and Zhaling Co well but reproduced those for Nam Co poorly. Through detailed analysis, we found that the simulated biases for Nam Co result largely from the unrealistic parameterization of eddy diffusivity. By expanding this parameter, the lake surface temperature simulations improved remarkably. In addition, erroneous lake ice cover simulations contributed to the simulated lake surface temperature bias in the cold seasons.  相似文献   

10.
CO2 fluxes were measured continuously for three years (2003?C2005) using the eddy covariance technique for the canopy layer with a height of 27 m above the ground in a dominant subtropical evergreen forest in Dinghushan, South China. By applying gapfilling methods, we quantified the different components of the carbon fluxes (net ecosystem exchange (NEE)), gross primary production (GPP) and ecosystem respiration (Reco) in order to assess the effects of meteorological variables on these fluxes and the atmospherecanopy interactions on the forest carbon cycle. Our results showed that monthly average daily maximum net CO2 exchange of the whole ecosystem varied from ?3.79 to ?14.24 ??mol m?2 s?1 and was linearly related to photosynthetic active radiation. The Dinghushan forest acted as a net carbon sink of ?488 g C m?2 y?1, with a GPP of 1448 g Cm?2 y?1, and a Reco of 961 g C m?2 y?1. Using a carboxylase-based model, we compared the predicted fluxes of CO2 with measurements. GPP was modelled as 1443 g C m?2 y?1, and the model inversion results helped to explain ca. 90% of temporal variability of the measured ecosystem fluxes. Contribution of CO2 fluxes in the subtropical forest in the dry season (October-March) was 62.2% of the annual total from the whole forest ecosystem. On average, 43.3% of the net annual carbon sink occurred between October and December, indicating that this time period is an important stage for uptake of CO2 by the forest ecosystem from the atmosphere. Carbon uptake in the evergreen forest ecosystem is an indicator of the interaction of between the atmosphere and the canopy, especially in terms of driving climate factors such as temperature and rainfall events. We found that the Dinghushan evergreen forest is acting as a carbon sink almost year-round. The study can improve the evaluation of the net carbon uptake of tropical monsoon evergreen forest ecosystem in south China region under climate change conditions.  相似文献   

11.
利用塔城地区9个国家气象观测站1961—2021年逐月降水资料,基于标准化降水量指数(SPI)运用最小二乘法和Mann-Kendall检验等方法分析塔城地区干旱时空分布特征。结果表明：(1)年尺度上,塔城地区干旱发生频率为30.37%,轻旱发生最多,中旱次之；2/3站点SPI呈显著增大趋势,年站次比和干旱强度呈显著减小趋势,干旱程度有所减轻,在1987年之后塔城干旱程度整体偏轻。(2)季节尺度上,夏、秋、冬季在1980年代中期发生干旱减轻的突变,且秋季和冬季分别在2002年和1997年达到显著。(3)在影响范围方面,各季以局域性和全域性干旱为主,全域性干旱发生频率介于20～30%之间；在干旱强度方面,各季轻度干旱发生频率最高,中度以上干旱发生频率介于33～38%之间。(4)近60a塔城地区季节性干旱呈现影响范围缩小,强度减弱的变化趋势,尤其是冬季干旱站次比和干旱强度分别以-7.79%.(10a)-1和-0.11.(10a)-1的倾向率显著减小,干旱减轻趋势在四季中最为显著。  相似文献   

12.
Industrial pollution has a significant effect on aerosol properties in Changsha City, a typical city of central China. Therefore, year-round measurements of aerosol optical, radiative and chemical properties from 2012 to 2014 at an urban site in Changsha were analyzed. During the observation period, the energy structure was continuously optimized, which was characterized by the reduction of coal combustion. The aerosol properties have obvious seasonal variations. The seasonal average aerosol optical depth (AOD) at 500 nm ranged from 0.49 to 1.00, single scattering albedo (SSA) ranged from 0.93 to 0.97, and aerosol radiative forcing at the top of the atmosphere (TOA) ranged from ?24.0 to 3.8 W m?2. The chemical components also showed seasonal variations. Meanwhile, the scattering aerosol, such as organic carbon, SO42?, NO3?, and NH4+ showed a decrease, and elemental carbon increased. Compared with observation in winter 2012, AOD and TOA decreased by 0.14 and ?1.49 W m?2 in winter 2014. The scattering components, SO42?, NO3? and NH4+, decreased by 12.8 μg m?3 (56.8%), 9.2 μg m?3 (48.8%) and 6.4 μg m?3 (45.2%), respectively. The atmospheric visibility and pollution diffusion conditions improved. The extinction and radiative forcing of aerosol were significantly controlled by the scattering aerosol. The results indicate that Changsha is an industrial city with strong scattering aerosol. The energy structure optimization had a marked effect on controlling pollution, especially in winter (strong scattering aerosol).  相似文献   

13.
Future changes of terrestrial ecosystems due to changes in atmospheric CO2 concentration and climate are subject to a large degree of uncertainty, especially for vegetation in the Tropics. Here, we evaluate the natural vegetation response to projected future changes using an improved version of a dynamic vegetation model (CLM-CN-DV) driven with climate change projections from 19 global climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5). The simulated equilibrium vegetation distribution under historical climate (1981–2000) has been compared with that under the projected future climate (2081–2100) scenario for Representative Concentration Pathway 8.5 (RCP8.5) to qualitatively assess how natural potential vegetation might change in the future. With one outlier excluded, the ensemble average of vegetation changes corresponding to climates of 18 GCMs shows a poleward shift of forests in northern Eurasia and North America, which is consistent with findings from previous studies. It also shows a general “upgrade” of vegetation type in the Tropics and most of the temperate zones, in the form of deciduous trees and shrubs taking over C3 grass in Europe and broadleaf deciduous trees taking over C4 grasses in Central Africa and the Amazon. LAI and NPP are projected to increase in the high latitudes, southeastern Asia, southeastern North America, and Central Africa. This results from CO2 fertilization, enhanced water use efficiency, and in the extra-tropics warming. However, both LAI and NPP are projected to decrease in the Amazon due to drought. The competing impacts of climate change and CO2 fertilization lead to large uncertainties in the projection of future vegetation changes in the Tropics.  相似文献   

14.
我国北方地区植被总初级生产力的空间分布与季节变化   总被引：3，自引：0，他引：3  
本研究通过集成Terra MODIS卫星影像数据与地面通量台站的观测数据, 改进了基于遥感的VPM光能利用率模型, 模拟了我国北方地区2008年陆地生态系统总初级生产力 (GPP) 的空间分布与季节变化。研究表明: (1) 我国北方地区植被GPP在空间分布上表现为东高西低的特征, 年均值为518.36 g/m2 (C重量, 下同)。 (2) 我国北方地区主要植被类型的GPP有较强的季节动态, 大体上都表现出单峰变化趋势。GPP值按照由大到小顺序依次为: 夏绿阔叶林 (DBF)>针阔混交林 (MF)>农田 (Crop)>落叶针叶林 (DNF)>常绿针叶林 (ENF)>草地 (Grass)>稀疏灌丛 (Oshrub)>裸地或稀疏植被 (BSV)。(3) 整个区域的GPP季相变化表现为: 夏季最高, 达到32.80 g?m-2?(8 d)-1, 为全年最大值; 春季GPP为5.67 g?m-2?(8 d)-1, 与秋季的5.08 g?m-2?(8 d)-1较为接近, 冬季GPP最弱, 仅为0.07 g?m-2?(8 d)-1。与通量台站实测值及前人研究结果的比较表明, 本文所模拟的GPP与观测值之间的相对误差绝对值多小于15%, 表明模拟结果具有较好的可靠性。这说明通过集成遥感观测数据与台站观测数据的方法来模拟GPP, 可以较准确地模拟区域尺度的GPP空间分布与时间变化, 这为深入研究陆气相互作用提供了重要研究手段。  相似文献   

15.
The environmental impact of aerosols is currently a hot issue that has received worldwide attention. Lacking simultaneous observations of aerosols and carbon flux, the understanding of the aerosol radiative effect of urban agglomeration on the net ecosystem carbon exchange(NEE) is restricted. In 2009-2010, an observation of the aerosol optical property and CO_2 flux was carried out at the Dongguan Meteorological Bureau Station(DMBS) using a sun photometer and eddy covariance systems. The different components of photosynthetically active radiation(PAR),including global PAR(GPAR), direct PAR(DPAR), and scattered PAR(FPAR), were calculated using the Santa Barbara DISORT Atmospheric Radiative Transfer(SBDART) model. The effects of PAR on the NEE between land-atmosphere systems were investigated. The results demonstrated that during the study period the aerosol optical depth(AOD)reduced the DPAR by 519.28±232.89 μmol photons · m~(-2)s~(-1);, but increased the FPAR by 324.93±169.85μmol photons ·m~(-2)s~(-1);, ultimately leading to 194.34±92.62 μmol photons · m~(-2)s~(-1); decrease in the GPAR. All the PARs(including GPAR,DPAR, and FPAR) resulted in increases in the NEE(improved carbon absorption), but the FPAR has the strongest effect with the light use efficiency(LUE) being 1.12 times the values for the DPAR. The absorption of DPAR by the vegetation exhibited photo-inhibition in the radiation intensity 600 photons · m~(-2)s~(-1); in contrast, the absorptions of FPAR did not exhibit apparent photo-inhibition. Compared with the FPAR caused by aerosols, the DPAR was not the primary factor affecting the NEE. On the contrary, the increase in AOD significantly increased the FPAR, enhancing the LUE of vegetation ecosystems and finally promoting the photosynthetic CO_2 absorption.  相似文献   

16.
The regional air quality modeling system RAMS-CMAQ was applied to simulate the aerosol concentration for the period 2045–2050 over China based on the downscaled meteorological field of three RCP scenarios from CESM (NCAR's Community Earth System Model) in CMIP5. The downscaling simulation of the meteorological field of the three RCP scenarios showed that, compared with that under RCP2.6, the difference in near-surface temperature between North and South China is weakened and the wind speed increases over North and South China and decreases over central China under RCP4.5 and RCP8.5. Under RCP2.6, from 2045 to 2050, the modeled average PM2.5 concentration is highest, with a value of 40–50 µg m−3, over the North China Plain, part of the Yangtze River Delta, and the Sichuan Basin. Meanwhile, it is 30–40 µg m−3 over central China and part of the Pearl River Delta. Compared with RCP2.6, PM2.5 increases by 4–12 µg m−3 under both RCP4.5 and RCP8.5, of which the SO42− and NH4+ concentration increases under both RCP4.5 and RCP8.5; the NO3− concentration decreases under RCP4.5 and increases under RCP8.5; and the black carbon concentration changes very slightly, and organic carbon concentration decreases, under RCP4.5 and RCP8.5, with some increase over part of Southwest and Southeast China under RCP8.5. The difference between RCP4.5 and RCP2.6 and the difference between RCP8.5 and RCP2.6 have similar annual variation for different aerosol species, indicating that the impact of climate change on different species tends to be consistent.摘要基于来自于 CMIP5 中 CESM 模式的三种 RCP 情景下的气象场的降尺度模拟, 应用区域空气质量模式系统 RAMS-CMAQ 模拟 2045-2050 年中国地区气溶胶浓度.三种 RCP 情景下气象场的降尺度模拟表明, 与 RCP2.6 相比, 在 RCP4.5 和 RCP8.5 下, 华北和华南的近地表温度差减小, 风速在华北和华南地区增加, 在中部地区下降. RCP2.6 情景下, 模拟的 2045 年到 2050 年平均的 PM 2.5浓度在华北平原, 长三角的部分地区和四川盆地最高, 约为 40-50 µg m–3, 在中国中部和珠三角的部分地区约为 30-40 µg m–3. 与 RCP2.6 相比, 在 RCP4.5 和 RCP8.5 下, PM2.5增加了 4-12 µg m–3, 其中在 RCP4.5 和 RCP8.5 下, SO42–和 NH4+的浓度增加, 在 RCP4.5 下, NO3–浓度降低, 在 RCP8.5 下, NO3–浓度升高, 在 RCP4.5 和 RCP8.5 下, BC 浓度变化很小, 而 OC 浓度下降, 其中在 RCP8.5 下, 西南和东南部分地区的 OC 有所增加.不同的气溶胶物种浓度在 RCP4.5 和 RCP2.6 之间的差异以及 RCP8.5 和 RCP2.6 之间的差异具有相似的年度变化, 这表明气候变化对不同物种的影响趋于一致.  相似文献   

17.
This study examines the potential impact of vegetation feedback on changes in summer climate aridity over the contiguous United States (US) due to the doubling of atmospheric CO2 concentration using a set of 100-year-long climate simulations made by a global climate model interactively coupled with a dynamic vegetation model. The Thornthwaite moisture index (I m ), which quantifies climate aridity on the basis of atmospheric water supply (i.e., precipitation) and atmospheric water demand (i.e., potential evapotranspiration, PET), is used to measure climate aridity. Warmer atmosphere and drier surface resulting from increased CO2 concentration increase climate aridity over most of the contiguous US. This phenomenon is due to larger increments in PET than in precipitation, regardless of the presence or absence of vegetation feedback. Compared to simulations without active dynamic vegetation feedback, the presence of vegetation feedback significantly alleviates the increase in aridity. This vegetation-feedback effect is most noticeable in the subhumid regions such as southern, midwestern and northwestern US, primarily by the increasing vegetation greenness. In these regions, the greening in response to warmer temperatures enhances moisture transfer from soil to atmosphere by evapotranspiration (ET). The increased ET and subsequent moistening over land areas result in weaker surface warming (1–2?K) and PET (3–10?mm?month?1), and greater precipitation (4–10?mm?month?1). Collectively, they result in moderate increases in I m . Our results suggest that moistening by enhanced vegetation feedback may prevent aridification under climatic warming especially in areas vulnerable to climate change, with consequent implications for mitigation strategies.  相似文献   

18.
东亚地区陆地生态系统的时空变率表现出明显的对季风气候的响应特征。使用EOF（经验正交分解）方法分析了AVIM2动态植被陆面模式离线模拟试验模拟的1953～2004年东亚季风区夏季陆地生态系统总初级生产力（GPP）、生态系统净初级生产力（NPP）、净生态系统初级生产力（NEP）、植被呼吸以及土壤呼吸的时空分布特点,探讨了东亚夏季风对陆地生态系统碳循环影响机制。研究发现,在强季风年,江淮地区高温少雨的特点限制了光合作用,造成GPP偏低;而华南地区在强季风年气候温暖湿润,利于植被生长,GPP偏高。季风对于植被呼吸和土壤呼吸影响不明显,使得GPP和植被呼吸之差NPP的变化及NPP和土壤呼吸之差NEP的变化与GPP的变化保持一致。在强季风年江淮流域地区干热的气候条件使得NPP和NEP降低;但是在华南地区温度升高的同时降水增多使得在NPP偏高的基础上NEP也偏高。  相似文献   

19.
利用1981、1996和2001年逐日南京站太阳总辐射和日照时数观测资料,建立了基于支持向量机(support vector machine,SVM)方法的太阳总辐射推算模型,预测了1982、1997和2002年的太阳总辐射,并把推算结果和采用线性的气候学方法所得到的推算结果分别与实测值进行对比。采用线性方法得到的1982、1997和2002年的太阳总辐射预测值与实测值间基于1:1线的决定系数(R~2)分别为0.800、0.859和0.838,均方根误差(RMSE)分别为3.250、2.649和2.925 MJ·m~(-2)·d~(-1)。采用SVM方法得到的1982、1997和2002年的R~2分别为0.894、0.938和0.936,RMSE分别为2.353、1.726和1.804 MJ·m~(-2)·d~(-1)。SVM方法得到的太阳总辐射预测值与实测值之间的误差较小,预测精度高于线性方法,更适用于实际太阳总辐射的计算。  相似文献   

20.
张华  卢鹏  荆现文 《大气科学》2015,39(1):137-144
本文首先构建了二流—四流球谐函数谱展开累加辐射传输的新方案,然后将其应用于国家气候中心第二代大气环流模式BCC_AGCM2.0.1的新版本中,并与模式中原有的Eddington累加方案进行了比较。由于新方案本质上是单层Eddington近似方案在四流上的推广。因此新方案在计算精度上要优于原方案。通过在全球气候模式中的应用与比较,本文发现新方案对气候模拟会产生比较大的影响。在晴空条件下,新方案计算的在南纬30°到60°区间、北大西洋东北部以及非洲北部的撒哈拉沙漠区域的地表向下年平均短波辐射通量要小于原方案结果,最大差别可以达到3.5 W/m2;同时,新方案计算的在南纬30°到60°区间和北大西洋东北部的大气顶向上年平均短波辐射通量要大于原方案结果,最大差别达到3 W/m2。在有云大气情况下,新方案计算的地表向下年平均短波辐射通量要小于原方案结果,并随着纬度的增加,新旧两种方案的差别逐渐变大,在南北极时达到最大5.5 W/m2;同时,新方案计算的在赤道区域的大气顶的年平均短波向上辐射通量要小于原方案结果,最大差别为2.5 W/m2,而在南北纬30°到60°区间,新方案计算的在大气顶的年平均短波向上辐射通量则要大于原方案结果,最大差别为1.5 W/m2。新方案计算的年平均短波加热率普遍高于原方案结果,特别是在800 hPa到地表之间的低层大气以及50 hPa到100 hPa的高层大气,最大差别可达0.03 K/d。因此,新方案有助于改善全球气候模式中普遍存在的赤道平流层中下层的温度冷偏差现象。  相似文献   

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