Identifying strengths and limitations of pan-European forest cover maps through spatial comparison

Detailed and harmonized information on spatial forest distribution is an essential input for forest-related environmental assessments, in particular, for biomass and growing stock modeling. In the last years, several mapping approaches have been developed in order to provide such information for Europe in a harmonized way. Each of these maps exhibits particular properties and varies in accuracy. Yet, they are often used in parallel for different modeling purposes. A detailed spatial comparison seemed necessary in order to provide information on the advantages and limitations of each of these forest cover maps in order to facilitate their selection for modeling purposes.

This article confronts the high-resolution forest cover map recently developed by the Joint Research Centre for the year 2000 (FMAP2000) with previously existing maps for the same time period: the CORINE Land Cover 2000 (CLC2000) and the Calibrated European Forest Map 1996 (CEFM1996). The spatial comparison of these three maps was carried out based on forest proportion maps of 1 km derived from the original maps. To characterize differences according to biogeographic regions, two criteria were used: detail of thematic content within each map and local spatial agreement.

Concerning thematic content, CLC2000 displayed a surfeit of non-forested areas at the cost of low forest proportions, while FMAP2000 showed a more balanced distribution likely to preserve more detail in forest spatial pattern. Good spatial agreement was found for CLC2000 and FMAP2000 within about 70% of the study area, while only 50% agreement was found when compared with CEFM1996. The largest spatial differences between all maps were found in the Alpine and Mediterranean regions. Reasons for these might be different input data and classification techniques and, in particular, the calibration of CEFM1996 to reported national statistics.     

A dimension-independent extrusion algorithm using generalised maps

One solution to the integration of additional characteristics, for example, time and scale, into GIS data sets is to model them as extra geometric dimensions perpendicular to the spatial ones, creating a higher-dimensional model. While this approach has been previously described and advocated, it is scarcely used in practice because of a lack of high-level construction algorithms and accompanying implementations. We present in this paper a dimension-independent extrusion algorithm permitting us to construct from any (n–1)-dimensional linear cell complex represented as a generalised map, an n-dimensional one by assigning to each (n–1)-cell one or more intervals where it exists along the nth dimension. We have implemented the algorithm in C++11 using CGAL, made the source code publicly available and tested it in experiments using real-world 2D GIS data sets which were extruded to construct up to 5D models.     

基于手机信令数据的深圳市二元居住空间迁居模式研究

迁居是城市空间重构的基础动力,了解其行为机制对改善住房结构、优化空间组织具有重要意义,然而目前针对大城市内部、正规与非正规二元居住空间并存的迁居研究仍较薄弱。本文基于生命历程理论与家庭迁居理论,利用2018年12月至2019年12月的手机信令等多源数据,识别深圳市二元居住空间分布和迁居流样本,从迁居流特征、邻里属性和二元空间类型三方面选取指标开展基于主成分分析的K-means聚类,探究迁居模式、结构特性与形成原因。结果表明：(1)非正规内部、正规与非正规交互、正规内部三层次迁居类型间存在年龄和居住质量递增的趋势,但均呈现通勤导向;(2)二元迁居的主体是短距离迁移,形成了4个大规模迁居网络集群,总体方向表现出郊区化趋势;(3)迁居模式可聚类为社区型、改善型、家庭型、事业型4类,结合二元空间分异影响呈现出8亚类,不同类型迁居群体属性和动因存在显著差别,总体反映出人们在不同生命历程下的迁居过程。最后,文章针对不同迁居模式提出差异化空间治理政策建议。     

基于手机定位数据的珠海市职住空间特征研究

深入分析职住平衡的概念及内涵，从时间和空间两个视角提出了两种职住平衡测度方法。采用移动手机定位数据对珠海居民的就业和居住空间分布、通勤距离、通勤来源进行了分析，同时测算了各规划分区的职住指数。结果表明：就业地与居住地在空间分布上保持较高的一致性；全市居民以短距离通勤为主，平均通勤距离为2048m，各规划分区的居民通勤距离存在较大差异；各规划分区有80%以上的居民实现了本地就业或居住。同时，从自然、规划、政策方面分析了职住影响因素，并提出了优化产业和人口空间配置、打通各规划分区之间交通瓶颈、合理配套公共服务设施等相关建议。     

An event simulation approach to the assessment of flood level frequencies: risk maps for the Warsaw reach of the River Vistula

Flood risk assessment is customarily performed using a design flood. Observed past flows are used to derive a flood frequency curve which forms the basis for a construction of a design flood. The simulation of a distributed model with the 1‐in‐T year design flood as an input gives information on the possible inundation areas, which are used to derive flood risk maps. The procedure is usually performed in a deterministic fashion, and its extension to take into account the design flood‐and flow routing model uncertainties is computer time consuming. In this study we propose a different approach to flood risk assessment which consists of the direct simulation of a distributed flow routing model for an observed series of annual maximum flows and the derivation of maps of probability of inundation of the desired return period directly from the obtained simulations of water levels at the model cross sections through an application of the Flood Level Frequency Analysis. The hydraulic model and water level quantile uncertainties are jointly taken into account in the flood risk uncertainty evaluation using the Generalized Likelihood Uncertainty Estimation (GLUE) approach. An additional advantage of the proposed approach lies in smaller uncertainty of inundation predictions for long return periods compared to the standard approach. The approach is illustrated using a design flood level and a steady‐state solution of a hydraulic model to derive maps of inundation probabilities. Copyright © 2016 John Wiley & Sons, Ltd.     

Two‐dimensional and three‐dimensional computational models in hydrodynamic and morphodynamic reconstructions of a river bend: sensitivity and functionality

This study assesses hydrodynamic and morphodynamic model sensitivity and functionality in a curved channel. The sensitivity of a depth‐averaged model to user‐defined parameters (grain size, roughness, transverse bed slope effect, transport relations and secondary flow) is tested. According to the sensitivity analysis, grain size, transverse bed slope effect and sediment transport relations are critical to simulated meander bend morphodynamics. The parametrization of grain size has the most remarkable effect: field‐based grain size parametrization is necessary in a successful morphodynamic reconstruction of a meander bend. The roughness parametrization method affects the distribution of flow velocities and therefore also morphodynamics. The combined effect of various parameters needs further research. Two‐dimensional (2D) and three‐dimensional (3D) reconstructions of a natural meander bend during a flood event are assessed against field measurements of acoustic Doppler current profiler and multi‐temporal mobile laser scanning data. The depth‐averaged velocities are simulated satisfactorily (differences from acoustic Doppler current profiler velocities 5–14%) in both 2D and 3D simulations, but the advantage of the 3D hydrodynamic model is unquestionable because of its ability to model vertical and near‐bed flows. The measured and modelled near‐bed flow, however, differed notably from each other's, the reason of which was left open for future research. It was challenging to model flow direction beyond the apex. The 3D flow features, which also affected the distribution of the bed shear stress, seem not to have much effect on the predicted morphodynamics: the 2D and 3D morphodynamic reconstructions over the point bar resembled each other closely. Although common features between the modelled and measured morphological changes were also found, some specific changes that occurred were not evident in the simulation results. Our results show that short‐term, sub‐bend scale morphodynamic processes of a natural meander bend are challenging to model, which implies that they are affected by factors that have been neglected in the simulations. The modelling of short‐term morphodynamics in natural curved channel is a challenge that requires further study. Copyright © 2014 John Wiley & Sons, Ltd.     

Preferential percolation quantified by large water content sensors with artifactual macroporous envelopes

For many scientific and practical tasks, it is important to estimate the soil–water percolation fluxes. This paper builds on measurements with large horizontal time‐domain reflectometry water content sensors in a loamy Mollisol. The sensors were installed into pre‐drilled holes and the gaps between them, and the soil was filled with a slurry of local soil with water. This gave rise to envelopes around them that contained artificial macropores. The sensors reacted to intensive rains by a rapid increase of their readings, often above the native soil's porosity, followed by an almost equally rapid decrease. The paper explores the feasibility of quantifying the rapid percolation, based on these anomalous water content peaks, and demonstrates that this is possible in principle, if the processes are simulated by a suitable model. A two‐dimensional dual porosity non‐equilibrium (mobile‐immobile) model was tried. The envelope around the sensor was modelled as an annulus with higher porosity and hydraulic conductivity, which attracts preferential flow and amplifies the percolation signal. With the model at hand, the flux hydrographs can be derived from model simulations and measured precipitation. For contrast, the Durner equilibrium dual porosity model was tried but was found little suitable. However, even the mobile‐immobile model did not perform perfectly. Simulated water contents were similar to the measured ones at some depths but not in the others, and the percolation fluxes were overestimated, compared to cumulative soil–water balance. Efforts to improve model performance were not successful. Hence, the model structure needs to be improved. Copyright © 2015 John Wiley & Sons, Ltd.     

2007年宁洱6.4级地震序列精定位

2007年6月3日在云南宁洱发生6.4级地震,震后云南省地震局在主震附近架设了5套流动数字地震台.利用这些地震台和思茅固定地震台记录的震相数据,采用双差定位法对宁洱6.4级地震的余震序列重新进行精定位.结果显示,宁洱地震序列的长度约为40km,宽度约为10km,明显集中在普洱断裂与NNE向断裂横断错移的构造部位,且大部...     

Regional mapping and characterisation of old landslides in hilly regions using LiDAR-based imagery in Southern Flanders

Analysis of LiDAR-derived imagery led to the discovery of more than 330 pre-Holocene to recent landslides in Southern Flanders (4850 km²). The morphology of three landslides, including the 266.5 ha deep-seated gravitational slope deformation in Alden Biesen, was investigated in more detail. The analysis of the morphological and topographical characteristics (width–length relation, frequency–area distribution and topographical threshold) of the landslides revealed important differences compared to the characteristics reported in other landslide studies, and helped understanding possible landslide triggering mechanisms. Especially the possibility of a seismic origin of the landslides was investigated. Finally, a heuristic model for region-wide landslide susceptibility mapping was successfully tested. The susceptibility model and map allow prediction of future landslide locations and contribute to better understanding the role of individual causal factors on landslide location and spatial density. The results suggest that landslides on low-gradient, soil-mantled hills are a more important contributor to landscape evolution of hilly areas than was hitherto thought. The morphology of all hilly regions of Flanders is clearly marked by landslide processes and higher landslide densities often coincide with the presence of quaternary active faults. This study further shows that high-resolution topographical data such as LiDAR significantly contributes to a better detection of old, previously unknown landslides.     

粤西沿海震动图的生成和研究

震动图是描绘地震产生的地面运动和可能破坏情况的有效工具,主要包括峰值地面速度(PGV)等值线图、峰值地面加速度(PGA)等值线图和仪器烈度分布图等.基于华南数字地震台网记录到的2010年7月9日MS3.7级阳江地震的数据资料,利用SAC和GMT软件从记录到的地震波形数据提取地面运动参数,生成了PGV和PGA等值线图,并...