ISWC OpenIR  > 水保所2018届毕业生论文
基于RegCM-CLM模式的植被覆盖变化对中国区域气候的影响
苟娇娇
Subtype硕士
Thesis Advisor王飞
2018-05
Degree Grantor中国科学院研究生院
Place of Conferral北京
Keyword区域气候模式 植被覆盖变化 气候反馈 情景模式 中国
Abstract区域尺度土地覆盖变化是自然变化和人类活动共同驱动的结果,同时又对区域气候环境产生反馈。本研究通过基于中国高精度土地覆盖资料、LAI卫星产品数据集及植被分区图等数据生成的高精度植被覆盖数据集,结合欧洲中值数值预报中心(ECMWF)ERA-Interim再分析资料,驱动RegCM4.5区域气候模式耦合陆面模式CLM4.5,开展1999—2009年不同植被覆盖情景模式的敏感性试验来模拟中国地表覆盖变化对区域气温与降水的影响;同时采用热量平衡及低层大气环流分析的方法对气温与降水变化机理进行了初步研究,评估植被覆盖变化对区域气温与降水量的影响方式。研究结果有:
(1)RegCM-CLM模式可以较好模拟中国区域气温与降水量的空间分布,与观测值有较好的一致性。模式对夏季气温和降水的模拟能力优于冬季,对降水模拟的精度不如气温。同时,RegCM4.5模式能够模拟出中国平均气温和降水的年间变化及年内变化,模拟与观测的气温与降水在时间尺度上的变化趋势大致相同,气候异常年份的峰值/低值处也较为匹配。RegCM4.5对气温与降水的年内循环有较好的模拟能力,可以很好地捕捉年内周期。
(2)植被覆盖变化的影响具有较明显的季节性差异,相较于冬季,植被覆盖变化对区域气候的影响在夏季较强。不同植被覆盖变化类型对气候反馈作用不同,中国南部农田转变为林地后,1999—2009年夏季平均气温升高,升高幅度在0.5 ℃以上;夏季降水量增加,增加幅度达80 mm。中国东北部草地转变为林地则与之相反,10 a间夏季平均气温下降,下降达1 ℃。当植被覆盖类型由灌木林地转变为草地时(非极地C3草/极地C3草),虽然草地对气温影响上较为一致,即都带来中国东部与青藏高原夏季平均气温下降,但青藏高原极地C3草对气温的作用较非极地C3草更强,夏季气温下降幅度更大,最小值达-4.47 ℃。不同种类草地对降水量影响不同,中国东部非极地C3草的增加使得夏季降水量增加,增加最大值达105.17 mm,而青藏高原极地C3草的增加使得夏季降水量减少。
(3)植被覆盖类型的改变,通过改变粗糙度、反照率、叶面指数等参数影响地面环流和能量平衡,引起降水和气温等发生变化。以中国南部为例,由于农田转变为自然植被,夏季反照率下降,地面粗糙度增加,叶面积指数增加,气孔阻力增大。反照率下降增加了地表吸收的太阳辐射,增加的吸收太阳辐射通过增加大气长波的损耗而有所抵消,使得净辐射(吸收的太阳辐射-净长波辐射)增加。净辐射的增加量主要通过植被的显热通量增加和潜热通量减少来平衡。这就要在更高的气温下才能使地表吸收的短波、发射的长波、输送的有效热通量达到新的平衡。另外,植被覆盖变化典型区域的风向和风速变化明显强于四周。我国青藏高原地区、中部地区上空受反气旋环流控制,表明夏季风强度总体偏弱,但在季风边缘区如中国东南部有所增强。近地面环流变化对区域降水量有一定影响。研究结果可促进对植被与气候变化关系的认识,又能为缓解区域气候变化环境影响和生态环境建设提供科学依据。
Other AbstractLand-cover change is driven by the natural climate change and human activities, in turn, the land-cover change also has impact on regional climate. In this paper, we produced a high resolution land cover datasets suited for model based on the high accuracy vegetation cover map, MODIS LAI datasets and the vegetation division map in China. In order to cognizing the impact of vegetation cover changes on regional temperature and precipitation over China, we conducted two sensitivity experiments numerical simulations (1999-2009) by using Regional Climate model RegCM4.5 coupled with the land surface model CLM4.5 under two different vegetation cover scenarios, which are driven by ERA-Interim reanalysis data produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). Meanwhile, we adopted two methods, surface heat balance analysis and atmospheric low circulation analysis to researching the mechanisms of air temperature and precipitation change and evaluating the pathways of vegetation cover changes, such as afforestation, affecting the regional air temperature and precipitation. The main conclusions of this study are summarized as follows:
(1) RegCM4-CLM is reliable for its ability to simulate the spatial distribution of air temperature and precipitation over China, and the simulated values are consistent with the observed values. Compared to the winter, the model performances on air temperature and precipitation are better in summer, and the accuracy of precipitation simulation is not as well as the temperature. Meanwhile, result shows an overall agreement between the observed and modelled inter-annual and annual changes in mean air temperature and precipitation over China. The tendency of simulated and observed temperature and precipitation changes are consistence in time scale, and the timing of simulated anomalies peaks are closely match the observed data. RegCM4.5 also is reliable for its ability to simulate the annual cycle of temperature and precipitation, and the inter-annual period can be well captured in the model.
(2) The impacts of vegetation cover changes on regional climate could be large in summer and small in winter and be different in different vegetation cover change types. An increase of the average 1999-2009 summer air temperature (warming range to above 0.5 ℃) and precipitation (wetting range to above 80 mm) were found in the south China where croplands was converted to forestland, which contrary to the conversion of grassland to forest land in northeast China, the average summer temperature were decreased(cooling range to reach 1 ℃). When the shrubland was replaced by grasslands (C3 Non Arctic Grass/Arctic Grass), although the impact of grassland on temperature are consistent in central China and the Tibetan Plateau, which brings about a decrease in summer temperature, but the C3 Arctic grass has a stronger effect on temperature than C3 Non Arctic grass with more temperature decreased (the minimum cooling value to reach -4.47 ℃) in the Tibetan Plateau. Different types of grassland also have different effects on precipitation. The increase of C3 Non Arctic grass resulted in an increase of the summer rainfall (the maximum wetting value to reach 105.17 mm) in central China, while the increase of C3 Arctic grass resulted in a decrease of the summer precipitation decrease in the Tibetan Plateau.
(3) The vegetation cover change can alter various physical characteristics of the land surface, including the land surface parameters such as roughness, albedo and leaf area index (LAI). All the changes in these parameters can influence the atmospheric low circulation and energy budget through the land-surface process, which has an effect on the air temperature and precipitation. In the South region of China for example, as a result of croplands being replaced by natural vegetation, summer and albedo decreased, roughness length increased, the sum of leaf area increased, and stomatal resistance increased. The summer albedo decreased which increased the solar radiation absorbed by the vegetation. The increased absorbed solar radiation was offset somewhat by increased longwave loss to the atmosphere so that net radiation (absorbed solar– net longwave) increased. This was balanced by an increase in vegetation sensible heat flux and a decrease in latent heat flux (canopy evapotranspiration). By analysis the energy budget in South region, it is necessary to reach a higher TX for make the short waves flux, the long waves, and the delivery of effective heat flux to a new balance. Moreover, there are significant changes in the near ground wind field in summer due to the vegetation cover change, and the changes of wind field are stronger in summer than in winter in terms of extent and scope. Changes in direction and speed of wind in typical vegetation cover change areas are significantly stronger than those in the surrounding area with unchanged vegetation. An anti-cyclonic circulation dominates in the Tibetan Plateau and central China, indicating that the summer monsoon intensity was generally weak, but it increased in the monsoon marginal regions such as southeastern China. Results indicate that near-ground circulation changes have a certain effect on regional precipitation. The research results can not only deepen the understanding of the relationship between vegetation and climate change, but also provide decision making for ecological environment construction, and for mitigating the environmental impact of regional climate change.
Subject Area水土保持与荒漠化防治
Language中文
Document Type学位论文
Identifierhttp://ir.iswc.ac.cn/handle/361005/8098
Collection水保所2018届毕业生论文
Affiliation中国科学院教育部水土保持与生态环境研究中心
Recommended Citation
GB/T 7714
苟娇娇. 基于RegCM-CLM模式的植被覆盖变化对中国区域气候的影响[D]. 北京. 中国科学院研究生院,2018.
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