Knowledge Resource Center for Ecological Environment in Arid Area
| 中国植被覆盖变化局地及区域气候效应的多源遥感研究 | |
| 其他题名 | Multiple satellite-based research of the impacts of vegetation cover change on local and regional biophysical climate effects in China |
| 马薇 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 贾根锁 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 地表与大气之间时刻进行着物质、能量和动量的交换。自然或者人类活动引起的植被覆盖变化通过改变地表特征来影响陆气间的物质和能量交换，进而影响局地和区域气候。这种生物物理气候效应被证明是全球重要的气候驱动力，但由于其存在高度的时空分异至今没有被纳入应对气候变化政策的考虑范围内。与低纬度和高纬度地区相比，中纬度地区植被覆盖变化引起的生物物理气候效应存在更大的不确定性，至今没有得到一致的研究结论。过去对中纬度生物物理气候效应的认识大部分来源于数值模拟实验。其优势是机理性强，但敏感性实验的非真实性、参数化方案的误差和粗网格尺度都使得模拟结果存在不确定性。基于站点的观测能够提供真实准确的、局地尺度的陆气相互作用过程，但是受到站点尺度的制约，难以在空间上进行拓展。近年来，随着遥感技术的进步和遥感数据的积累，多源遥感对地观测提供了独立的、高时间精度和高空间分辨率的连续观测，能够帮助提取地表特征因子和气候因子的时空分异特征，尤其对于理解中纬度地区由于植被覆盖变化引起的高时空分异的生物物理气候效应有独特的优势。中国地处中纬度区域，植被覆盖变化具有空间上的复杂性和时间上的易变性，是研究植被覆盖变化引起的生物物理气候效应的良好的“试验场”。本文以中国为例，综合了2003-2014年包括MODIS、CERES、SRTM在内的多源遥感观测平台研究中国潜在植被覆盖变化引起的生物物理气候效应及其纬度、季节及时空分布特征，并从地表能量平衡的角度揭示了地表特征改变（包括地表反照率和地表蒸散）对地表温度变化的决定作用。本文为进一步研究中纬度区域地表过程和气候变化提供了遥感观测依据，并为未来区域高精度气候模拟提供了有益的地表过程信息。本文重点研究5种植被覆盖变化，包括：森林和农田、森林和草地、中国北方地区的草地和农田，以及和灌丛相关的两种植被覆盖变化，包括森林和灌丛、灌丛和农田。使用的MODIS产品全部进行了严格的数据质量控制，其中地表温度数据还进行了海拔高度控制。主要研究结论如下：1、森林相较于周围的农田的地表温度效应具有日不对称性，即白天具有制冷效应，夜晚具有增温效应。区域平均而言，森林日平均地表温度效应为-0.31±0.02℃。随着纬度由低到高，森林白天制冷效应减弱，夜晚的增温效应增强，日平均地表温度效应由制冷转换为增温的转换纬度为北纬40-48°。季节方面，森林日平均地表温度效应表现为冬季增温，春、夏、秋季降温。森林相较于周围农田的地表温度差时空分布特征表现出高度的时空异质性。仅从温度角度分析，这种复杂性是由森林白天和夜晚的地表温度效应不对称造成的。森林的温度日较差（DTR）小于农田，在北纬20-39°主要表现为日最高地表温度低，在大于北纬50°地区主要表现为日最低地表温度高，中纬度森林对周围环境具有温度调节作用。森林比周围农田的地表反照率低。同时比农田的地表蒸散值高。森林和农田间地表反照率差异和地表蒸散差异都随纬度增加而减小。季节方面，地表反照率差异在冬季出现明显低值，在夏季出现相对高值。地表蒸散差异在5、6月份出现最高值，而森林在冬季并不比农田具有蒸散优势。对于森林和农田之间的转换，地表反照率变化引起的对太阳短波辐射吸收的差异和地表蒸散变化引起的潜热通量释放差异在中纬度的作用机制有两种。在25°N以南地区和在25°N以北地区的夏季，短波辐射吸收差与潜热通量差作用方向相反，即森林比农田多吸收短波辐射能量并且多释放潜热通量，潜热通量差的制冷作用超过了短波辐射吸收差的增温作用，地表温度差异的空间格局主要继承潜热通量差的特征，表现为降温；在25°N以北地区的冬季，短波辐射吸收差与潜热通量差作用方向相同，即森林比农田多吸收短波辐射能量并且少释放潜热通量，两者共同起到增温作用，地表温度差异的空间格局主要继承太阳短波辐射差异的特征。当森林覆盖变化发生时，地表反照率和地表蒸散改变的时空格局能够决定地表温度的时空格局，并且地表感热通量的改变和地表温度的差异也呈现出相似的时空分布格局，表明地表温度改变导致的能量收支能够被感热通量补偿。2、森林相较于周围的草地的地表温度效应与上述森林和农田间的地表温度效应类似，区别在于其在纬度间和年际间变化较为缓和，考虑与自然草地不受人为灌溉影响有关。森林和草地间的地表特征变化也与上述森林和农田间的地表特征差异类似，并且地表反照率和地表蒸散共同引起的能量变化也能够很好的解释地表温度变化的纬度、季节及时空分布特征。3、对中国北方地区农牧交错带和新疆绿洲灌溉区的自然草地和农田之间的潜在转换研究表明：草地相较于农田在白天和夜晚都具有增温效应，日平均增温幅度为0.49±0.03℃。草地和农田的地表温度差异基本不随纬度改变，但是有明显的季节特征：非生长季草地和农田的地表温度类似，但生长季内草地的温度显著高于农田。地表特征分析表明，草地比农田的地表蒸散值低，且主要表现在生长季内，非生长季内两者的地表蒸散值基本相同。同时，草地的地表反照率更高。地表能量分析表明，生长季和非生长季内地表蒸散差异引起的潜热通量的差异是造成草地和农田地表温度差异的主要原因，地表反照率差异引起的短波辐射吸收差异主要影响非生长季的地表温度差异。由于之前缺乏自然草地和农田（包括灌溉和雨养农田）生物物理气候效应的研究，本研究得到的结论对未来高精度气候模拟的参数化方案有一定参考作用。4、灌丛覆盖变化的地表温度效应介于森林和农田之间，即：区域平均而言，农田向灌丛转换有降温效应，而森林向灌丛转换有增温效应。灌丛发生转换时的地表特征差异也介于森林和农田之间。一方面，灌丛比森林的地表反照率高，比森林的地表蒸散值低；另一方面，灌丛比农田的地表反照率地低，比农田的地表蒸散值高。对于灌丛覆盖变化，地表反照率和地表蒸散变化引起的能量收支改变同样能够在季节、纬度和时空分布角度决定地表温度的变化。 |
| 英文摘要 | Changes of land cover regulate climate system directly through the alteration of water vapor, energy and momentum exchange between land surface and the atmosphere. Although long recognized scienti?cally as being important, these so-called biophysical effects are rarely included in climate change adaptation and mitigation policies due to the many challenges associated with their highly spatial and temporal heterogeneity. Biophysical effects vary with locations and seasons, and cause regional cooling or warming. However, the largest uncertainty exhibit in the mid-latitudes. Until now, the sign and magnitude of biophysical effect of vegetation cover change in temperate zones are still under debate.Research progress on the biophysical climate effect of vegetation cover change is hindered by certain limitations of existing methodology. In modelling approaches, global climate models still cannot reproduce local climate effects reliably due to their coarse spatial resolution and uncertainties in physical processes, parameterization, and input data. For observational approach, in situ measurements (for example, Fluxnet, ?eld experiments, and weather stations) can provide local evidence to verify model results. But in most cases, ?eld data are collected from geographically restricted areas. With the accumulation of remote sensing data in the past ten years, satellite-based studies provide independent, repeated and consistent observations to investigate the impacts of vegetation conversion on climate, especially in temperate zones with highly spatial and temporal heterogeneity.China has experienced dramatic vegetation cover changes in the 21st century, which is largely driven by anthropogenic land use practices and various natural causes. Here we focus on the climate response to potential vegetation cover changes in China between 18-53°N. Multi-sensor satellite data, including SRTM derived digital evaluation model, MODIS derived land cover classification, LST, ET, albedo, and CERES radiation data products are implied in this study. The main contribution of this study are: 1) to better understand biophysical climate effects of vegetation cover conversion in mid-latitudes; 2) to better understand the biophysical mechanisms behind those effects in terms of the changing surface energy induced by albedo and ET.This study focus on 5 kinds of vegetation cover change, including forest and cropland conversion, forest and grassland conversion, grassland and cropland conversion in the northern part of China, forest and shrubland conversion, and shrubland and cropland conversion. All MODIS products are used with data quality control, and the MODIS LST product are also controlled by elevation. The main conclusions in this study are as follows:1. The average annual daytime and nighttime land surface temperature difference between forest and cropland shows an asymmetric diurnal variation, with a larger magnitude in daytime cooling than nighttime warming. For regional average, forest shows a daily net cooling effect of -0.31±0.02℃. From the latitudinal perspective, forest shows an average daily cooling effect within 18-39°N and an average daily warming effectwithin 49-53°N. In the transition zone of 40-48°N, the effect is negligible. From the seasonal perspective, forest presents daily cooling in spring, summer autumn, and daily warming in winter. Forest has smaller daily temperature range with cropland, which mainly cause by a lower maximum LST in 20-39°N and by a higher minimum LST to the north of 50°N.Forest shows lower albedo and higher ET than adjacent cropland. And the albedo difference and ET difference increase across the latitude.Albedo difference is lower in winter and higher in summer. ET difference shows noticeable high in May and June and nearly zero during the wintertime.From the surface energy budget perspective, the changes of albedo induced shortwave radiation absorptionand ET induced latent heat can largely determine the direction and magnitude of land surface temperature response to deforestation or afforestation. Here we find that two biophysical mechanisms work in the temperate region by checking the spatio-temporal patterns of albedo difference and ET difference. First, compared with cropland, more solar radiation absorbed and less latent heat released by forest dominate the north of 25°N in cold seasons, implying negative albedo difference and negative ET difference work in the same direction. Second, forest absorbs more solar radiation and releases more latent heat to the south of 25°N in all seasons as well as to the north of 25°N in warm seasons, which means that negative albedo difference and positive ET difference work in a competitive way. This result reflects the complexity of biophysical mechanisms in the mid-latitude. Furthermore, the net effect of albedo induced short radiation difference and ET induced latent heat difference shows similar latitudinal and seasonal trend and similar spatiotemporal pattern with LST difference, meaning that albedo and ET is the determiant factor in shaping LST. Sensible heat difference also shows similar spatiotemporal pattern with LST difference, which imply the LST difference induced surface energy change is compensated by altered sensible heat.2. The biophysical climate effects between forest and grassland is similar with that between forest and cropland, with a more moderate change between latitude and season. The biophysical properties changes can also well explain LST difference, which means that the net effect of albedo induced short radiation difference and ET induced latent heat difference presents similar pattern with LST difference.3. Arid and semi-arid areas experienced significant conversion between natural grasslands and croplands in recent decades along farming-pastoral ecotones in the northern China. In this study, natural grassland is found warmer than nearby cropland (including irrigated and rainfed cropland) in both daytime and nighttime, with a net daily warming effect of 0.49±0.03℃. LST difference is similar among differenct latitude and shows obvious seasonal trend. Grassland had lower ET in growing seasons and nearly the same ET in non-growing seasons, compared with cropland. Graassland has higher albedo than cropland. Surface energy budget analysis reveals that LST difference between grassland and cropland is primarily determined by the net effect of ET induced latent heat changes, and followed by albedo induced solar radiation absorption changes. These findings may contribute to next generation climate model parameterization, and provide policy support for climate adaptation and mitigation.4. The climate effects of shrubland related vegetation cover change is between forest and short vegetation. Cropland conversion to shrubland cause cooling and forest conversion to shrubland cause warming. The biophysical properties change of shrubland related vegetation cover conversion is also between forest and short vegetation. On the one hand, shrubland has higher albedo and lower ET than nearby forest. On the other hand, shrubland has lower albedo and higher ET than adjactent cropland. For shrubland cover change, the net effect of albedo induced short radiation difference and ET induced latent heat difference can also change the latitudinal, seasonal and spatiotemporal pattern of LST difference. |
| 中文关键词 | 中纬度植被覆盖变化 ; 生物物理气候效应 ; 地表能量平衡 ; 时空分布特征 ; 多源卫星遥感观测 |
| 英文关键词 | Temperate vegetation cover change Biophysical climate effect Surface energy budget Spatiotemporal pattern Multiple satellite-based observations |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 气象学 |
| 来源机构 | 中国科学院大气物理研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287855 |
| 推荐引用方式 GB/T 7714 | 马薇. 中国植被覆盖变化局地及区域气候效应的多源遥感研究[D]. 中国科学院大学,2017. |
| 条目包含的文件 | 条目无相关文件。 | |||||
| 个性服务 |
| 推荐该条目 |
| 保存到收藏夹 |
| 导出为Endnote文件 |
| 谷歌学术 |
| 谷歌学术中相似的文章 |
| [马薇]的文章 |
| 百度学术 |
| 百度学术中相似的文章 |
| [马薇]的文章 |
| 必应学术 |
| 必应学术中相似的文章 |
| [马薇]的文章 |
| 相关权益政策 |
| 暂无数据 |
| 收藏/分享 |
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。
