Robustness of the holistic seismic risk evaluation in urban centers using the USRi

The Urban Seismic Risk index (USRi) published in a previous article (Carreño et al., Nat Hazards 40:137–172, 2007) is a composite indicator that measures risk from an integrated perspective and guides decision-making for identifying the main interdisciplinary factors of vulnerability to be reduced or intervened. The first step of the method is the evaluation of the potential physical damage (hard approach) as a result of the convolution of the seismic hazard with the physical vulnerability of buildings and infrastructure. Subsequently, a set of social context conditions that aggravate the physical effects is also considered (soft approach). According to this procedure, the physical risk index is evaluated for each unit of analysis from existing loss scenarios, whereas the total risk index is obtained by multiplying the former index by an impact factor using an aggravating coefficient, based on variables associated with the socio-economic conditions of each unit of analysis. The USRi has been developed using the underlying holistic and multi-hazard approach of the Urban Risk Index framework proposed for the evaluation of disaster risk in different megacities worldwide. This article presents the sensitivity analysis of the index to different parameters such as input data, weights and transformation functions used for the scaling or normalization of variables. This analysis has been performed using the Monte Carlo simulation to validate the robustness of this composite indicator, understanding as robustness how the cities maintain the ranking as well as predefined risk level ranges, when compared with the deterministic results of risk. Results are shown for different cities of the world.     

Assessment of wetland fragmentation in the Tarim River basin, western China

The wetlands in the middle and lower reaches of the Tarim River are a rich area of biodiversity and natural resources in the inland arid region of China. However, this wetland area has decreased in size during the past several decades. Water quality and biodiversity has declined due to expanded agricultural activities since 1960s. Using remote sensing (RS), geographic information system (GIS) and global positioning system (GPS) techniques, we investigated the dynamics, spatial patterns and fragmentation of the wetlands in the middle and lower reaches of the Tarim River from 1980 to 2000. We found that the total area of the wetlands was reduced by 45.8% and the density of the patches increased four times from 1980 to 1990. From 1990 to 2000, though the total area of the wetlands slightly increased the number of the patches increased three times and the density of the patches doubled. Based on the analyses of transition matrixes, diversity and fragmentation indexes, and spatial distribution alternation of the wetlands, we found the landscape diversity and fragmentation indices increased while wetland dominance index decreased dramatically. Among the wetland types, the areas of the river-channel, reservoir and pond wetlands increased while the areas of the lake and marsh wetlands decreased continuously.     

Statistical Distributions of Hydraulic Conductivity from Reliability Analysis Data

This paper describes a first-order reliability-based analysis to identify the best-fit probability distributions for hydraulic conductivity. The analysis involved the use of existing hydraulic conductivity model developed from laboratory data and applied to lateritic soils, considering variations in soil parameters. Plots of reliability indices versus coefficients of variation were first made for hydraulic conductivity as well as for initial degree of saturation, plasticity index and clay content, considering three compactive efforts and log-normally distributed hydraulic conductivity. The traditional two-parameter log-normal distribution was compared to four alternative distributions: normal, gamma, Gumbel (extreme value type I-EVT-I) and Weibull (extreme value type III-EVT-III). The analysis showed that the Weibull and normal are the best-fit probability distributions for the hydraulic conductivity based reliability data. Hydraulic conductivities predicted from reliability analysis were used to demonstrate the possibility of applying the results obtained in this research by practising engineers. Experimentally-determined hydraulic conductivities were shown to be in good agreement with predicted values.     

科尔沁沙地典型区域地表环境变化与气候变化的响应关系

以科尔沁沙地阿古拉苏木为典型代表区域, 应用1987-2006年20 a间12幅遥感影像及相应气候数据, 分析了地表环境变化与气候变化间的响应关系, 提出了表征响应敏感程度、影响程度大小排序的气候因子影响指数(CFII). 结果表明: 近20 a研究区地表环境变化表现为不断恶化的趋势. 各类地表环境变化与气候因子变化间有着良好的响应关系, 各类气候因子变化以不同方式和过程不同程度地影响着地表环境的变化. 响应敏感度最大, 即对地表环境变化影响最大的是相对湿度, 其次为降水量和蒸发量. 水分条件是制约干旱半干旱地区地表环境变化的主导因素.     

中国3个典型城市气溶胶光学厚度地基观测及其MODIS气溶胶产品精度分析

利用中国太阳分光观测网的观测资料结合MODIS(中分辨率成像光谱仪)的气溶胶产品分析了北京、兰州、上海3个典型区域城市的气溶胶光学特性。结果表明:北京AOD(气溶胶光学厚度)年平均为0.41±0.35,春夏高,秋冬低,Angstrm波长指数α年平均为1.40±0.85表现为细模态粒子,MODIS的光学厚度为0.52±0.39与地面观测相关系数为0.91,存在系统性高估;兰州AOD年平均为0.55±0.21,夏季最低,秋冬较高,α年平均为0.95±0.20表现为粗模态粒子,MODIS光学厚度为0.43±0.21与地面观测相关系数仅为0.07,存在系统性低估;上海AOD年平均为0.55±0.21,无明显季节变化,α平均为1.03±0.25,MODIS光学厚度为0.74±0.30与地面观测相关系数为0.75,存在系统性高估。城市地理位置和复杂地表等原因造成反照率的不确定,MODIS气溶胶产品在这3个城市的反演效果仍有很大提升空间。     

青藏高原上空甲烷的时空分布特征及其夏季高值形成机制分析

利用搭载在美国Aqua卫星上的大气红外探测仪(AIRS)观测资料反演的全球甲烷(CH_4)产品和NCEP再分析资料,分析了2003~2014年青藏高原上空CH_4的时空变化特征,探讨了夏季CH_4高值变化与季风的关系。研究结果表明:就青藏高原整体而言,CH_4浓度随高度增加递减;对流层中高层CH_4含量季节变化较为明显,其平均浓度在7~9月处于高值,6月、10月次之,其余月份处于低值。2003~2014年CH_4含量呈逐年上升趋势,年增长率约为4.66ppb(10-9)。高原上空CH_4空间分布分析显示,高原北部CH_4浓度高于南部地区。夏季风期间,随着高原上的强对流输送和上空南亚高压的阻塞,对流层中高层CH_4浓度明显增加并不断积累,在8月底至9月初出现最大值。在分析季风指数的基础上发现,夏季季风影响下的强对流输送是高原对流层中高层CH_4高值形成的主要原因之一,对流层中高层CH_4浓度最大值出现时间较季风指数的峰值滞后约半至一个月,随着夏季风的撤退,CH_4浓度高值迅速降低。     

1960~2011年中国日降水集中程度的时空变化特征

利用1960~2011 年的日降水资料,计算降水集中指数（Concentration Index,CI）,分析中国区域降水集中程度的空间分布及时间变化特征,得到以下主要结论：CI 指数可有效描述我国日降水集中程度;我国CI 指数介于0.575 与0.750 之间,平均为0.652,总体呈现出东部大、西部小,夏季大、冬季小的特征;44.17%站点的CI 指数表现出增加趋势,55.83%的站点表现出减少趋势,其中10.36%站点的变化趋势通过95%信度水平的显著性检验,CI 指数显著增大的站点主要分布在西北、华中和西南地区,显著减小的站点主要分布在东北、华北、东南沿海及青藏高原东部等地区;3~5 年是各子区域CI 指数变化的主要周期,与对应区域降水量的变化周期较一致;1970 年左右和2000 年左右是显著周期性变化出现较集中的时间段。     

基于MODIS数据不同荒漠植被指数的空间变化研究--以新疆三工河流域为例

通过对三工河流域的实例研究,探讨了干旱区不同下垫面荒漠植被指数的空问变化规律。采用植被信号／土壤噪音对15个植物样方数据进行对比分析,探讨了三工河流域荒漠植被指数的梯度变化及适宜性。结果表明：扇缘溢出带植被指数值最高,其次是山前丘陵带和固定沙丘,较真实地反映出了三工河流域荒漠植被的梯度变化规律;扇缘溢出带的EVI值要比NDVI值离散程度小,趋势平稳,在扇缘溢出带用EVI能更好地反映植被生长状况;山前丘陵带的NDVI值要比EVI值均匀,山前丘陵区用NDVI这一植被指数较好,扇缘溢出带和固定沙丘区用EVI要比用NDVI好。     

河口和沿岸海域的富营养化评价模型

河口和沿岸海域富营养化评价模型和方法,已经从以营养盐为基础的第1代评价体系发展到当前的以富营养化症状为基础的第2代多参数富营养化评价模型和方法。重点介绍了2种有代表性的、被广泛应用的河口和沿岸海域富营养化评价方法：综合评价法(OSPAR-COMPP)和河口营养状况评价法(ASSETS),比较和评价了这2种方法的特点、异同和优缺点,并建议尽快建立适合我国河口和沿岸海域特点的富营养化评价模型和方法以及相应的监测和管理体系。     

基于植被指数的高光谱遥感水陆识别方法初探

提出了一种判别两类地物分类效果的依据——显著性度量,并采用植被指数的形式,给出了应用高光谱图像进行水陆识别的方法。以滩涂为例进行水陆识别实验,结果表明,基于显著性度量遴选得到的最佳植被指数类型及其最佳波段组合,适合于解决以高光谱图像为数据源的水陆识别问题。