家庭或学校植被水平与儿童青少年肥胖水平间的关联

[背景]植被暴露水平与儿童青少年肥胖水平的关联性研究证据尚不一致,且多来自发达国家和地区,我国的研究证据相对较少。[目的]评估基于卫星遥感数据估计的植被覆盖水平与儿童青少年肥胖水平的关联。[方法]2016-2018年,在中国珠三角地区3个城市52316名5~18岁儿童青少年中开展了一项横断面研究,通过问卷调查获得基本社会人口学特征和肥胖水平。应用陆地遥感卫星(Landsat)数据和中分辨率成像光谱仪(MODIS)产品评估研究对象所在学校和家庭周围的植被水平,计算家庭或学校所在500 m和1000 m缓冲区半径内的归一化植被指数(NDVI)、植被覆盖率(VCF)、土壤调整植被指数(SAVI)、增强型植被指数(EVI)。应用二水平广义线性模型评估不同植被暴露水平下的儿童青少年相对于最低植被暴露水平下的体重指数z分值(zBMI)变化和相对超重风险,并采用限制性立方样条评估暴露-反应关系。采用反事实框架模型评估PM_(2.5)和NO_(2),以及体育锻炼水平在其关联上的中介作用。研究最终纳入的52316名儿童中,8406人(16.1%)为超重。植被水平与儿童青少年的zBMI呈现出非线性的暴露-反应关联,当植被达到一定水平时,儿童青少年zBMI降低。按照植被水平四分位数分组,调整协变量后,与处于NDVI_(500m)和VCF_(500m)最低四分位组的儿童青少年相比,处于最高四分位组的儿童青少年zBMI和超重风险更低:家庭处于NDVI_(500m)第四四分位组的儿童青少年zBMI值相对于第一四分位组的变化量(b)为-0.07(95%Cl:-0.10~-0.04),超重OR为0.92(95%Cl:0.85~0.99)。当使用1000 m缓冲半径和SAVI、EVI时,观察到了与500 m缓冲半径植被暴露对儿童肥胖水平类似的负相关关联。中介分析结果显示:调整协变量后,最高NDVI_(500m)四分位组中,家庭和学校周围空气污染分别介导了NDVI_(500m)与儿童青少年zBMI负向关联的50%(95%Cl:20%~80%)、90%(95%Cl:50%~160%),未观察到体育锻炼水平的中介效应。[结论]家庭或学校周围更高的植被水平可能与儿童青少年较低的zBMI、超重风险相关,并且这种关联可能部分是通过降低空气污染物浓度实现的。

2000—2018年甘南州植被覆盖水平时空变化

基于2000—2018年MODIS EVI数据,采用Theil-Sen Median趋势分析法、Mann-Kendall检验和多元线性回归分析,研究甘南州EVI时空变化趋势和影响因素。结果表明,从年际EVI变化来看,2000—2018年甘南州草地生长季植被覆盖度呈先下降再缓慢上升的趋势,EVI均值在0.36~0.41。从空间变化看,盛草期甘南州绝大部分区域植被覆盖度较高且随时间推移而明显改善;部分地区发生了轻微退化现象。具体可以表现为高海拔地区植被退化较明显,而低海拔地区植被有改善的趋势。影响植被变化趋势的主要因素是气候和地形因素,人为因素也有显著影响。

植被对城市热岛效应影响的研究进展

热岛效应导致城市人居热环境恶化,并造成能源的巨大消耗,如何有效缓解热岛效应已成为迫切需要解决的问题。植被可以通过遮蔽长短波辐射和蒸腾等作用起到降低气温、增加湿度的效果,因此,城市绿化已成为一种缓解热岛效应的重要技术手段。为继续推动植被对城市热岛效应影响的研究,分别从研究现状、研究内容和研究方法、存在问题与展望等方面对国内外的相关研究进行梳理与综述。首先从城市热岛效应的研究起源、观测方式等角度梳理了国内外的研究进展。在此基础上,进一步分析了植被对城市气温的调节机理,并分别从植被垂直结构、水平结构、冠层结构等空间结构视角与植被遥感指数视角,进一步对植被的降温效应机理进行了综述。其中,植被冠层结构包含叶面积指数、冠幅、郁闭度、绿量等参数,遥感指数包含归一化植被指数、植被覆盖度、绿度植被指数等参数。除对国内外的研究现状进行综述外,还总结了目前绿地降温效应研究中的主要问题,并在未来研究方向等方面提出建议,为后续研究提供借鉴和参考。

基于不同地貌类型区甘南州植被覆盖时空变化及其影响因素研究

甘南藏族自治州(简称甘南州)位于青藏高原东北边缘,处在第一阶梯与第二阶梯的过渡区,地貌类型复杂多变,且在不同地貌区的植被覆盖差异十分明显。基于2000—2018年MODIS EVI数据研究甘南州不同地貌区植被覆盖时空变化趋势及其影响因素。结果表明:(1)从时间变化上来看,2000—2018年甘南州西北部山原区、东部山地丘陵区和南部岷迭山谷区增强植被指数(EVI)增长趋势分别为0.0008、0.0011和0.0009 a^(-1)。(2)从空间变化上来看,甘南州植被覆盖度(FCV)呈现由西南部向东北部逐渐递减的空间分布特征,其中,西北部山原区以较高覆盖度类型为主,东部山地丘陵区以中等覆盖度类型为主,南部岷迭山谷区呈现较低覆盖度与较高覆盖度类型的相间分布。(3)甘南州植被覆盖改善比例(约54%)高于退化比例(37%),其中,植被覆盖退化区主要分布在西北部山原区的玛曲、碌曲及南部山谷区的迭部等地;植被覆盖改善区主要分布在东部山地丘陵区。(4)甘南州不同地貌区EVI的影响因素有所不同,自然环境因子和人类活动因子是影响西北部山原区EVI的主要影响因素,而自然环境因子是东部山地丘陵区、南部岷迭山谷区EVI的主要影响因素。

Vegetation Development and Water Level Changes in Shenjiadian Peatland in Sanjiang Plain,Northeast China

This paper documents a 7800-year proxy record from the Shenjiadian peatland on the Sanjiang Plain in Northeast China.High-resolution plant macrofossil and colorimetric humification methods were used to reconstruct the vegetation and hydrologic history from a 193 cm-long sedimentary profile.Detrended correspondence analysis(DCA) was applied to transform the raw plant macrofossil data into latent indices of peatland water level.The vegetation community transited from an Equisetum fluviatile community to a Carex lasiocarpa community at approximately 3800 cal yr BP and was followed by a Carex-shrub community at approximately 480 cal yr BP.Based on the plant macrofossil DCA axis 1 scores and humification values,we distinguished four hydrologic periods:a wet period from 7800 cal yr BP to 4500 cal yr BP,dry periods up to 1600 cal yr BP,drier periods until 300 cal yr BP,and the driest period from 300 cal yr BP until the present.Through a comparison with other climate records,we suggest that the East Asian summer monsoon(EAM) was the main driving force for vegetation and water level changes to the Shenjiadian peatland through its impacts on precipitation.

Research on the Summer Drought in Chongqing Using MODIS-EVI Time Series Data

MODIS-EVI time series data from 2000 to 2009 in Chongqing were selected for this study.By the use of best index slope extraction （BISE） method for cloud elimination,analysis on the change vector of EVI time series data were conducted to investigate the EVI response on drought; then,four typical regions were selected to study the relationship between precipitation,temperature and EVI when the sever drought occurred in 2006; finally,based on the time series of vegetation condition index （VCI） and precipitation abnormity percentage,the temporal and spatial distributions of drought were studied.The results showed that,the EVI value of the summer in 2006 was significantly lower than the average EVI at the corresponding period of the other years in Chongqing.In addition,summer drought occurred mainly during the hot and dry weather.Except the southeast area,most of the other regions in Chongqing were all under severe drought.

Analytical Models for Velocity Distributions in Compound Channels with Emerged and Submerged Vegetated Floodplains

The lateral distributions of depth-averaged velocity in open compound channels with emerged and submerged vegetated floodplains were analyzed based on the analytical solution of the depth-integrated Reynolds-Averaged Navier-Stokes equation with a term to account for the effects of vegetation.The three cases considered for open channels were two-stage rectangular channel with emerged vegetated floodplain,rectangular channel with submerged vegetated corner,and two-stage rectangular channel with submerged vegetated floodplain,respectively.To predict the depth-averaged velocity with submerged vegetated floodplains,we proposed a new method based on a two-layer approach where flow above and through the vegetation layer was described separately.Moreover,further experiments in the two-stage rectangular channel with submerged vegetated floodplain were carried out to verify the results.The analytical solutions of the cases indicated that the corresponding analytical depth-averaged velocity distributions agree well with the simulated and experimental prediction.The analytical solutions of the cases with theoretical foundation and without programming calculation were reasonable and applicable,which were more convenient than numerical simulations.The analytical solutions provided a way for future researches to solve the problems of submerged vegetation and discontinuous phenomenon of depth-averaged velocity at the stage point for compound channels.Understanding the hydraulics of flow in compound channels with vegetated floodplains is very important for supporting the management of fluvial processes.

Vegetation and Topographic Control on Spatial Variability of Soil Organic Carbon

Soil organic carbon (SOC) is one of the most important parameters affecting the hydraulic characteristics of natural soils. Despite being rather easy to measure, SOC is known to be highly variable in space. In this study, vegetation, climate, and morphology factors were used to reproduce the spatial distribution of SOC in the mineral horizons of forest and grassland areas in north-western Italy and the feasibility of the approach was evaluated. When the overall sample (114 samples) was analyzed, average annual rainfall and elevation were significant descriptors of the SOC variability. However, a large part of the variability remains unexplained. Two stratification criteria were then adopted, based on vegetation and topographic properties. We obtained an improvement of the quality of the estimates, particularly for grasslands and forests in the absence of local curvatures. These results indicate that the spatial variability of soil organic matter is scarcely reproducible at the regional scale, unless an a-priori reduction of the heterogeneity is applied. A discussion on the feasibility of applying stratification criteria to deal with heterogeneous samples closes the paper.