青藏高原湿地土壤冻结、融化期间的陆面过程特征   总被引：4，自引：0，他引：4       下载免费PDF全文

张海宏  肖宏斌  祁栋林  李甫 《Acta Meteorologica Sinica》2017,75(3):481-491

利用青藏高原中部玉树隆宝湿地2015年7月-2016年7月的观测资料,分析了土壤冻结、融化前后土壤温、湿度和地表能量收支特征,结果表明：冻土持续时期为12月至次年4月,深层土壤的冻结较浅层土壤滞后,融化过程快于冻结过程,5-40 cm土壤全部冻结历时51 d,全部融化历时19 d。土壤体积含水量年变化幅度达0.6 m³/m³。冻结过程5-40 cm土壤体积含水量下降,融化过程5-10 cm土壤体积含水量升高。土壤冻结之后,感热通量白天的值升高,潜热通量白天的值降低,净辐射和土壤热通量均降低,土壤热通量日变化幅度增大。土壤融化之后,潜热通量、净辐射和土壤热通量白天的值升高。地表反照率、鲍恩比、土壤热导率和土壤热扩散率冻结后增大融化后减小,土壤热容量冻结后减小融化后增大。  相似文献   

Geologically constrained changes to landforms caused by human activities in the 20th century: A case study from Fukuoka Prefecture,Japan     

《Applied geography (Sevenoaks, England)》2017

Human activity has been recognized to be an important geomorphic agent, and the resulting changes to landforms and land cover are regarded as a global problem. Although there has been much research into the relationships between geomorphic processes and types of land use such as agriculture, mining, and urbanization, it is important to clarify spatiotemporal human impacts on topography on a regional scale when predicting future changes in land cover.This study examined changes in land use to clarify the distribution and impact of anthropogenic changes to landforms, as well as the influence of geology on the extent of these changes. In a case study from Fukuoka Prefecture, Japan, changes in land use over the last century were analyzed using a geographic information system (GIS). The study area, which covers approximately 4930 km², has experienced urban development since 1950 and has a current population of over 5 million. Land use data were prepared using paper-based early editions of topographic maps. Subsequently, the distribution of anthropogenic landforms was evaluated by comparing landforms with regional geological data.GIS analysis using our prepared land use data, landform data, and regional geological data has clarified the following characteristics of the study area. (1) Land uses prior to 1950 were constrained by topographic relief. After 1950, land use was characterized by urban sprawl. Urban areas expanded and contained both higher elevations and steeper slopes at their margins. The relationships between land uses and landforms during this urbanization are unclear. (2) The area of urban land increased in the geological regions with Paleogene sedimentary rocks (PSD) and Mesozoic granitic rocks (GR) during the 20th century. The largest coal mining area in Japan was located in the PSD geological regions, and ancient iron working was common in the GR geological regions, particularly during the 7th century. This result indicates that the land use distribution, especially urban areas in sloping terrain, is related to the regional geology. (3) Deforestation related to land use resulted in steeper terrain in forest land in the PSD and GR geological regions. These changes to landforms in forest areas occurred as a result of rapid urban sprawl and have created many new boundaries between forest areas with steeper slopes and urban areas with gentler slopes. This phenomenon may have caused an increase in the frequency of sediment-related disasters.This case study indicates that predictions of anthropogenic changes to landform, which are important for the assessment of global climate change and natural hazards, must clarify the relationships between land uses, landforms, and regional geology.  相似文献   

Four decades of urban sprawl and population growth in Teresina,Brazil     

《Applied geography (Sevenoaks, England)》2017

The expansion of medium-sized cities in Brazil has increased significantly since the 80–90's decades. In that period, most of the urbanization process was represented by the agglomeration of the population in the major metropolitan areas such as São Paulo and Rio de Janeiro. Nowadays, the rural-urban movement in Brazil is predominantly affecting cities with less than 1 million inhabitants, located particularly in the Center-West and in the Semiarid Northeast regions. The city of Teresina, the capital and largest city of the Brazilian state of Piauí, is one example that has shown an accelerated process of urban development. In this context, this paper seeks to discuss the urban sprawl of Teresina over the last four decades (1974–2014), associating its trends of urban expansion and population growth with their social and environmental implications. The results of our work indicate that urban sprawl in Teresina has been continuous over the years and getting faster in the 2010–2014 period. High demographic density areas are located mostly in peripheral zones, where the low-income population dominates. The population density varies across the city, and it is far from the standard proposed by the urban legislation. Thus, urbanization in Teresina is characterized by the sprawl of its municipal boundaries, intra-urban densification and verticalization, and an increase in population, especially in areas of low-income neighborhoods.  相似文献   

Land cover changes and landscape pattern dynamics in Senegal and Guinea Bissau borderland     

《Applied geography (Sevenoaks, England)》2017

Different levels of climatic, agricultural, demographic, political and socioeconomic change have been detected in West African countries. For many years the human impact on the region was negligible, due to the low population density. However, in the last decades, demographic increase has accelerated exploitation of the natural resources and consequently the degradation of the ecosystems. Land cover degradation and landscape changes are more or less pronounced according to politic and socio-economic conditions of each country. In this study, a region located on the borderland of north Guinea-Bissau and south Senegal, is analyzed with regard to land cover and landscape trends, considering the socio-economic factors that drive them and the borderline effect. In this analysis, remote sensing data (Landsat TM, ETM+ and OLI data) were used to obtain four land cover maps for the years 1990, 2002, 2010 and 2015. The results show a similar landscape behavior in both countries, directly related to similar socio-economic practices. Forest area increase in both countries and there is a reduction in Agriculture/Bare soil areas until 2010. Main causes may be associated to the rural exodus, resulting from the conflict for independence of Casamance, which affects the borderland region of Senegal and Guinea Bissau, or to the conversion of agricultural areas into cashew orchards. In opposition, between 2010 and 2015, Forest area decrease and Agriculture/Bare soil increase, due to the recent trend of conversion of old cashew orchards into traditional fields of cereals and peanut. An increase in landscape fragmentation is observed in the period under analysis, revealing a heterogenization trend, which can be related to the adoption of similar human practices, in the last decades.  相似文献   

Global SMOS Soil Moisture Retrievals from The Land Parameter Retrieval Model     

《International Journal of Applied Earth Observation and Geoinformation》2016

A recent study by Van der Schalie et al. (2015) showed good results for applying the Land Parameter Retrieval Model (LPRM) on SMOS observations over southeast Australia and optimizing and evaluating the retrieved soil moisture (θ in m³ m⁻³) against ground measurements from the OzNet sites. In this study, the LPRM parameterization is globally updated for SMOS against modelled θ from MERRA-Land (MERRA) and ERA-Interim/Land (ERA) over the period of July 2010–December 2010, mainly focusing on two parameters: the single scattering albedo (ω) and the roughness (h). The Pearson's coefficient of correlation (r) increased rapidly when increasing the ω up to 0.12 and reached a steady state from thereon, no significant spatial pattern was found in the estimation of the single scattering albedo, which could be an artifact of the used parameter estimation procedure, and a single value of 0.12 was therefore used globally. The h was defined as a function of θ and varied slightly for the different angle bins, with maximum values of 1.1–1.3 as the angle changes from 42.5° to 57.5°.This resulted in an average r of 0.51 and 0.47, with a bias (m³ m⁻³) of −0.02 and −0.01 and an unbiased root mean square error (ubrmse in m³ m⁻³) of 0.054 and 0.056 against MERRA (ascending and descending). For ERA this resulted in an r of 0.61 and 0.53, with a bias of −0.03 and an ubrmse 0.055 and 0.059. The resulting parameterization was then used to run LPRM on SMOS observations over the period of July 2010–December 2013 and evaluated against SMOS Level 3 (L3) θ and available in situ measurements from the International Soil Moisture Network (ISMN). The comparison with L3 shows that the LPRM θ retrievals are very similar, with for the ascending set very high r of over 0.9 in large parts of the globe, with an overall average of 0.85 and the descending set performing less with an average of 0.74, mainly due to the negative r over the Sahara. The mean bias is 0.03, with an ubrmse of 0.038 and 0.044. In this study there are three major areas where the LPRM retrievals do not perform well: very dry sandy areas, densely forested areas and over high latitudes, which are all known limitations of LPRM. The comparison against in situ measurement from the ISMN give very similar results, with average r for LPRM of 0.65 and 0.61 (0.64 and 0.59 for L3) for the ascending and descending sets, while having a comparable bias and ubrmse over the different networks. This shows that LPRM used on SMOS observations produce θ retrievals with a similar quality as the SMOS L3 product.  相似文献   

Major forest changes and land cover transitions based on plant functional types derived from the ESA CCI Land Cover product     

《International Journal of Applied Earth Observation and Geoinformation》2016

Land use and land cover change are of prime concern due to their impacts on CO₂ emissions, climate change and ecological services. New global land cover products at 300 m resolution from the European Space Agency (ESA) Climate Change Initiative Land Cover (CCI LC) project for epochs centered around 2000, 2005 and 2010 were analyzed to investigate forest area change and land cover transitions. Plant functional types (PFTs) fractions were derived from these land cover products according to a conversion table. The gross global forest loss between 2000 and 2010 is 172,171 km², accounting for 0.6% of the global forest area in year 2000. The forest changes are mainly distributed in tropical areas such as Brazil and Indonesia. Forest gains were only observed between 2005 and 2010 with a global area of 9844 km², mostly from crops in Southeast Asia and South America. The predominant PFT transition is deforestation from forest to crop, accounting for four-fifths of the total increase of cropland area between 2000 and 2010. The transitions from forest to bare soil, shrub, and grass also contributed strongly to the total areal change in PFTs. Different PFT transition matrices and composition patterns were found in different regions. The highest fractions of forest to bare soil transitions were found in the United States and Canada, reflecting forest management practices. Most of the degradation from grassland and shrubland to bare soil occurred in boreal regions. The areal percentage of forest loss and land cover transitions generally decreased from 2000–2005 to 2005–2010. Different data sources and uncertainty in the conversion factors (converting from original LC classes to PFTs) contribute to the discrepancy in the values of change in absolute forest area.  相似文献   

Integrating the system dynamic and cellular automata models to predict land use and land cover change     

《International Journal of Applied Earth Observation and Geoinformation》2016

Land use and land cover change (LULCC) is a widely researched topic in related studies. A number of models have been established to simulate LULCC patterns. However, the integration of the system dynamic (SD) and the cellular automata (CA) model have been rarely employed in LULCC simulations, although it allows for combining the advantages of each approach and therefore improving the simulation accuracy. In this study, we integrated an SD model and a CA model to predict LULCC under three future development scenarios in Northern Shanxi province of China, a typical agro-pastoral transitional zone. The results indicated that our integrated approach represented the impacts of natural and socioeconomic factors on LULCC well, and could accurately simulate the magnitude and spatial pattern of LULCC. The modeling scenarios illustrated that different development pathways would lead to various LULCC patterns. This study demonstrated the advantages of the integration approach for simulating LULCC and suggests that LULCC is affected to a large degree by natural and socioeconomic factors.  相似文献   

基于GIS的岷江上游流域土地利用／覆被变化研究     

李茂娇  杨斌  詹金凤  高桂胜  王世举 《测绘工程》2016,25(6):41-45

以岷江上游流域为对象,选取3期9景TM/+ETM遥感影像,通过多步骤最大似然监督分类、变化检测,结合空间动态分析测算模型,分析近20年土地利用/覆被变化情况。结果表明:从整个流域分析,林地面积减少,主要转化为未利用地、建设用地和耕地;未利用地在前8年以每年3.7%、后8年以每年0.4%的速度增加;建设用地在1994—2002年以每年34%的速度增加,到2002—2010年增长速度减缓;耕地总面积减少54 431hm2;从县域分析,1994—2002年间,松潘和黑水县大面积林地转为未利用地;2002—2010年间,松潘县未利用地转为林地和建设用地,茂县和汶川县未利用地面积大幅增加。该研究结论不仅为国土资源管理部门优化土地利用结构提供依据,亦为当地政府实现生态资源可持续发展提供数据支撑。  相似文献   

南海北部海区无柄蔓足类的分布   总被引：4，自引：1，他引：4  

严文侠  董钰  王华接  严涛  严岩  梁冠和 《海洋与湖沼》1995,26(4):414-422

于1986－1991年在南海北部对16个海洋结构物上的无柄蔓足类水平分布、垂直分布和个体大小进行调查。研究表明，所采集到的标本隶属于无柄蔓足类的3科7属19种，其中藤壶科5属16种，笠藤壶科1属2种和小藤壶科1属1种。共有17种无柄蔓足类分布在珠江口东南海区；而琼东海区仅发现2种；琼东南海区有8种；莺歌海海区11种和北部湾海区10种。纵肋巨藤壶、美丽藤壶和珠江藤壶为珠江口东南海区特有种。研究无柄蔓足类在南海北部近海海区的分布及其与海流的关系，不仅有助于深入了解该类生物的生活习性和生态特点，也为海洋石油平台的设计及污损生物的防除提供参数。  相似文献   

南海北部海区有柄蔓足类的生态特点   总被引：7，自引：1，他引：7  

严文侠  董钰  梁冠和  王华接  严岩  严涛 《海洋与湖沼》1995,26(4):423-430

于1986－1991年，在南海北部对17个海洋结构物进行调查，以了解有柄蔓足类的种类组成、分布状况和个体大小。结果表明，所采集的标本有2科4属8种，它们分别是茗荷属的荷、鹅荷和印度荷；条荷属的细板条荷、条荷和百条荷；软荷属的太平洋软荷及异荷属的日本异荷。荷、鹅荷和细板条荷几乎分布在所有浮标站，其附着密度随着离岸距离的增加而增大；荷和鹅行可分别在0－80m和0－75m水层中分布，而细板条荷则从表层一直分布到150m深处。该类生物属外海性种类，只附着在漂浮或能移动的物体表面，而不栖息于固定式海洋结构物。  相似文献