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132.
This study examines the land-use/cover change (LUCC) dynamics and drivers for two prominent land-use/cover systems in Guatemala: natural forests (FOR) and coffee agroforests (CAF). To-date, very little research has examined the LUCC dynamics of CAF, in large part due to the high degree of spectral similarity that exists between agroforests and other forest-cover types. Given the ecosystem and livelihood services provided by shade-grown coffee production, it is increasingly necessary to map and identify the dynamics and drivers of CAF changes over space and time. This research uses remote sensing analysis, land transition matrices, and multinomial regression models to examine LUCC dynamics over two ten-year intervals (1990–2000; 2000–2010) in Guatemala. Spatially explicit biophysical (e.g. slope, elevation) and accessibility (e.g. distance to roads) factors are used to model and compare drivers of change for CAF and FOR. Results demonstrate LUCC dynamics and drivers for the two land-use/cover systems to be complex over space and time. For example, FOR losses are evident for both time intervals, largely associated with conversion to CAF and croplands (CPL) in low slope, low altitude areas, and in areas close to existing croplands, respectively. CAF losses are also evident in the 1990s, but are outpaced by expansion in the 2000s. Losses are associated with conversion to CPL, particularly near roads and existing croplands, while expansion and/or persistence of CAF occurs near cities. These results suggest that conservation programs aimed at tree cover preservation and expansion should consider natural forests and managed agroforests separately. Further, such programs should be tailored to specific locations and institutional settings given the influence of topography and accessibility factors in determining localized patterns of landscape transformations over space and time. 相似文献
133.
气象台站网的布局优化可以提高气象台站观测资料的代表性、准确性和可比较性.简述了气象台站网布局优化方法的国内外研究进展,讨论了气象台站网布局优化方法的关键技术和存在的问题,重点介绍和分析了利用线性内插法、最优内插法、信息论法、因子分析法和经验模式法来进行气象台站网的布局优化,总结了这些方法的可行性.结合气象业务需求变化,提出了气象台站网布局优化方法的改进方向. 相似文献
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综合考虑农田生态系统中水、热、CO2输送所涉及的大气、水文、生物等生物物理过程,以Farquhar等提出的叶片尺度光合作用生物化学过程机理模型为理论基础,对其进行空间尺度扩展,并改进冠层分层方法,建立了均匀农田与大气之间物质输送和能量交换的多层模式,在模式中运用双叶模型,同时考虑叶片氮素水平垂直差异,对2008年4—5月华北平原冬小麦生长旺季农田生态系统中冠层CO2通量进行了模拟研究,并利用涡度相关观测的通量数据对模型的有效性加以验证,结果表明:在冠层多层空间,小麦拔节至孕穗期和开花至乳熟期叶片氮含量随冠层高度的衰减系数分别为0.793(R2=0.698)和1.374(R2=0.728),冠层内叶片氮含量的空间分布可以用以相对累积叶面积指数为自变量的函数来描述;模型分别计算各层阴、阳叶的光截取、气孔传导、光合作用等,最终计算冠层上方CO2通量,冬小麦农田净生态系统生产力模拟值与实测值相关显著(R2=0.78),模拟的CO2通量日变化特征晴天昼间比阴雨天和夜间的效果好;在考虑丛聚影响的叶片非随机分布的密集农田中,阴叶对总初始生产力的贡献率在35.7%左右,对生产力贡献很重要。分层统计显示,作物最终产量的形成主要... 相似文献
138.
The summertime phytoplankton bloom near the Kerguelen Plateau is in marked contrast to the low-chlorophyll conditions typical of the Southern Ocean and is thought to arise from natural iron fertilisation. The mechanisms of iron supply to the euphotic zone in this region are poorly understood, and numerical studies of iron transport have until now omitted fine-scale (sub-mesoscale) dynamics which have been shown to significantly increase vertical transport in other parts of the ocean.We present the first sub-mesoscale-resolving study of the flow and vertical transport in this region. The modelled transport and flow structure agree well with observations. We find that an increase in horizontal resolution from mesoscale-resolving (1/20°) to 1/80° resolves sub-mesoscale filamentary frontal structures in which vertical velocities are dramatically higher and are consistent with available observations. Lagrangian tracking shows that water is advected to the surface from much greater depth in the sub-mesoscale-resolving experiment, and that vertical exchange is far more rapid and frequent. This study of sub-mesoscale vertical velocities sets the foundation for subsequent investigation of iron transport in this environment. 相似文献
139.
The assessment of drought relief by typhoon Saomai based on MODIS remote sensing data in Shanghai,China 总被引：1，自引：1，他引：0
Typhoons are one of the major natural hazards occurring frequently in Shanghai. The comprehensive assessment of drought relief by typhoon has become a major concern of scientists and government agencies in Shanghai, China. In this article, with the support of remote sensing data and the available data from local meteorological stations, the regional drought relief was investigated and the change of drought intensity was quantified by the typhoon “Saomai” between 5 and 8 August 2005. The precipitation anomaly calculated on the basis of recorded rainfall was adopted to analyze drought condition changes before and after the typhoon. Then, vegetation supply water index (VSWI) and normalized difference vegetation index (NDVI) were used to monitor the drought relief due to the consecutive shortage of summer rainfall. Impact of typhoon on drought was compared by VSWI before and after typhoon Saomei. The results showed that the typhoon alleviated the drought of the vegetation by more than 70 %, based on the spatial and temporal distribution of precipitation, the ground temperature, relative humidity, high temperature, NDVI from Shanghai area. The result shows that MODIS remote sensing data are a useful quantitative monitoring tool in drought relief by local typhoons. More strategies are necessary to be adopted for prevention and mitigation of meteorological disaster in Shanghai in recent years. 相似文献
140.
The relationship between monthly vegetation cover anomalies and climate in the Hulunbei'er steppe were studied through analyzing the relationship between regional normalized difference vegetation index (NDVI) and climatic variables, and NDVI and tree-ring width during the growing season (May–October). The local moisture (dry/wet) and temperature (cold/warm) variations largely affected the vegetation cover and the radial growth of Mongolian pines (Pinus sylvestiris Linnaeus var. mongolica Litvinov) in the steppe. Monthly precipitation and Palmer drought severity index (PDSI) data from the previous to the current growing seasons were positively correlated to regional vegetation cover and radial growth of Mongolian pines; however, negative correlations were found between temperature and vegetation variables. A reconstruction of monthly vegetation cover dynamics for the growing season was created and spans 116 years (from 1891 to 2006). The results show that the total numbers of anomalies for dense and sparse seasonal vegetation cover is 22 years over the 116 year record; about 5–7 relatively dense or sparse periods; and ∼2–8 years significant periodicities (p < 0.05). Linkages to the Pacific Ocean and Arctic Ocean regimes were also detected. 相似文献