2021年3月中旬东亚中部沙尘天气地面起尘量及源区贡献率估算

2021年3月中旬,东亚中部包括中国北方大部分地区,爆发了持续性的沙尘天气,引发了人们对于沙尘源区、防风固沙生态建设工程效益的高度关注.提出了一个新的地表起尘量估算方法,使用高精度、大范围的气象数据,计算了这次沙尘天气的地面起沙条件、大风过程中的输沙状况,估算了不同时刻的起尘量,获得了14、15日蒙古和中国北方荒漠地区...     

Wind tunnel simulation of the effects of freeze–thaw cycles on soil erosion in the Qinghai–Tibet Plateau

Intense freezing and thawing actions occur in the Qinghai–Tibet Plateau because of its high elevation and cold temperature. The plateau's unique environment makes it easy to generate wind erosion under dry, windy weather conditions, resulting in the emergence of desertification. As a major form of freeze–thaw erosion, freeze–thaw and wind erosion is displayed prominently on the Qinghai–Tibet Plateau. Therefore, in this study, soil samples were collected from the surface of the plateau to undergo freeze–thaw and wind erosion simulation experiments. Results show that wind erosion strength increases with an increasing number of freeze–thaw cycles, water content in the freezing–thawing process, and the difference in freeze–thaw temperatures. Therefore, in the conditions of water participation, the main reason for the freeze–thaw and wind erosion in the Qinghai–Tibet Plateau is the damage to the soil structure by repeated, fierce freeze–thaw actions, and the sand-bearing wind is the main driving force for this process. The research results have theoretical significance for exploring the formation mechanism of freeze–thaw and wind erosion in the Qinghai–Tibet Plateau, and provide a scientific basis for freeze–thaw desertification control in the plateau.     

台特玛湖干涸湖盆两种典型风蚀坑的三维流场特征及对风蚀的影响

台特玛湖干涸湖盆区风蚀沙漠化快速发展,发育了以新月形沙丘和风蚀坑（主要为槽状坑和碟状坑）为主的风沙地貌。风蚀坑的发育不仅受来流风影响,还与坑内三维流场有关。基于风洞实验和计算机流体力学（Computational fluid dynamics, CFD）数值模拟,对风蚀坑三维流场进行了探究。结果表明：（1） 从入风侧到出风侧,槽状风蚀坑和碟状风蚀坑底面的风速均呈减速—加速—减速—加速的变化模式,上口所在水平面的风速变化呈加速—减速—加速变化模式,上口气流压强也相应地发生变化,槽状风蚀坑和碟状风蚀坑整体呈低压—高压—低压变化模式,其中槽状坑变化更为明显。（2） 两种形状风蚀坑对气流均具有一定的吸附效应,使坑外一定范围的风沙流被吸入坑内,聚集能量和风沙流,加剧风蚀坑风蚀发育。（3） 风蚀坑加剧了地表侵蚀,侵蚀程度与风蚀坑尺度有关,风蚀坑尺度越大,对地表侵蚀越强。本文直观展示了两种典型风蚀坑中的三维速度、压力、风沙流流向分布,揭示了风蚀坑的风沙流吸附机制,研究结果可加深对风蚀坑形态动力学的理解,也可为内陆干涸湖盆沙漠化防治提供理论指导。     

塔里木河下游不同生活型植被对地表的防护效果

在干旱区植被生态建设过程中,需要进行决策并经常引起争论的问题是,究竟应该选择哪种生活型植被才能获得最大的防护效果.为比较不同生活型植被对地表防护效果的差异,本文选取塔里木河下游6种常见乔灌草植被,以降低风速百分比的平均值作为植被对地表防护效果的评价指标,对不同生活型植被对地表防护效果进行定量比较.结果表明:上述6种植被防风性能大小次序依次为:花花柴>罗布麻>骆驼刺>柽柳>盐穗木>胡杨.花花柴对地表防护效果最好,降低地表风速百分比的平均值达44.00%,胡杨对地表防护效果最差,降低地表风速百分比平均值13.21%.就乔、灌、草不同生活型植被而言,防护效果大小次序为:多年生草本>灌木>乔木.因此,从生态防护效应角度来说,在干旱区植被生态建设中,应坚持灌、草先行的原则,乔木植被只能在水分条件较优越的地区适度发展.只有这样才能充分利用有限的水资源, 取得最佳的生态防护效应.     

基于航空口岸的台胞大陆 旅游流空间场效应分析

为克服缺乏研究分析所需的各源点(旅游目的地)间旅游流的流量、流向数据,本文基于网络分析原理的数据库分析技术,对航空口岸选择变化所引起的台胞大陆旅游流空间场效应进行模拟分析。研究发现,以广州－广州,上海－上海为入出境口岸的客流联系比较发育,其次是北京－北京、上海－广州(或广州－上海),而选择北京－上海(或上海－北京),北京－广州(或广州－北京)为入出境口岸的旅游流空间场发育较为薄弱。造成这种空间效应的主要原因是受到旅游资源区位供给、旅游者市场需求(如产品偏爱,旅游时间限制)、旅游交通(航空网络连接强度和紧密度)及旅行社营销等共同影响。研究结果为入境台胞区域旅游合作与发展提供参考依据。     

Wind tunnel investigation of the influence of surface moisture content on the entrainment and erosion of beach sand by wind using sands from tropical humid coastal southern China

Wind erosion has major impacts on dune growth, desertification, and architecture on sea coasts. The deflation threshold shear velocity is a crucial parameter in predicting erosion, and surface moisture greatly affects this threshold and thus sand stability. Wind tunnel studies have shown that reduced moisture contents decrease entrainment thresholds and increase wind erosion, but field and wind tunnel test data is lacking for tropical humid coastal areas. In this study, we investigated the influence of surface moisture contents (at 1 mm depth) on sand entrainment and erosion using tropical humid coastal sands from southern China. Shear velocities were deduced from velocity profiles above the sand. The threshold shear velocity increased linearly with increasing ln100M (M, gravimetric moisture content). The increase was steepest below a moisture content of 0.0124 (i.e., at M_1.5, the moisture content in the sand at a matric potential of − 1.5 MPa). We compared several popular models that predict threshold shear velocity of moisture sediment, and found substantial differences between their predicted results. At a surface moisture content of 0.0124, the predicted increase in the wet threshold shear velocity compared with the dry threshold shear velocity ranged from 34% to 195%. The empirical model of Chepil and Selah simulated the data well for M < 0.0062 (i.e., 0.5M_1.5), whereas Belly's empirical model simulated the data best for M > 0.0062. Wind erosion modulus increased with increasing effective wind velocity following a power function with a positive exponent at all moisture contents, but decreased with increasing surface moisture content following a power function with a negative exponent. When wind speed and moisture content varied simultaneously, wind erosion modulus was proportional to the 0.73 power of effective wind velocity, but inversely proportional to the 1.48 power of M. The increase in resistance to erosion at low moisture contents probably results from cohesive forces in the water films surrounding the sand particles. At a moisture content near M_1.5, wind erosion ceases nearly for all wind velocities that we tested.     

A field investigation into the effects of progressive rainfall-induced soil seal and crust development on runoff and erosion rates: The impact of surface cover

Surface crusts and seals can form from a variety of processes, both physical and biological, and have the potential to alter runoff and erosion, especially in regions with low vegetation covers. Despite the obvious links between seals and crusts these features have rarely been considered together. This study uses rainfall simulation experiments to investigate interrill soil crust and seal development in response to structural (or raindrop-impact-induced) and depositional (or runoff-induced) processes on a semiarid piedmont in southern New Mexico, USA, which has undergone substantive vegetation change (replacement of grasses by shrubs) over the last 100 years. The study design incorporates six double-paired runoff plots divided into four subplots, each of which was exposed to three rainfall simulation events. Crust development on these plots was assessed using penetration-resistance measurements while seal development was assessed using runoff coefficients. The penetration-resistance data indicate that subplots directly exposed to raindrop impacts (uncovered plots) have crusts that are  40% stronger than those positioned beneath a mesh cover (covered plots) that intercepts the kinetic energy of the rainfall. The crusts exposed to raindrop-impacts increased in strength following each simulation, whereas the crusts on the covered surfaces reached a plateau after two events.Runoff data indicate that seal development does not directly mirror crust formation. Runoff coefficients increased after each rainfall simulation event but were not significantly different between the covered and uncovered plots. Rather, the presence of stone lags or litter on the soil surface influenced the relation between runoff and seal development. Sediment yields from uncovered surfaces exceeded those from covered surfaces, indicating that raindrop impacts contribute to the delivery of sediment into flows. The results of this study indicate that the loss of vegetation cover on the piedmont has increased the extent of surface crust and seal development but that those crusts may be playing an important role in mitigating erosion.     

中国城市化水平的自回归与功率谱分析

利用1949~2000年的城市人口比重数据,开展中国城市化过程的自相关和功率谱分析,建立了ARMA (1,q )模型。中国的城市化过程具有1阶自相关特征:上一年的一个变动直接影响下一年,间接影响则可达10年之久。ARMA (1,q)模型表明中国的城市化过程在趋势性上附加有丰富的随机性。对提取趋势之后的序列进行功率谱分析,发现趋势性和随机性的背后隐含一个长度为30年左右的周期波动。根据上述研究,将中国的城市化过程分解为三种变动:趋势性、周期性和随机性。研究结论对发展更为完善的城市化预测方法,以及对指导具有中国特色的城市化建设,都可能具有一定程度的启示意义。     

基于SD的水质型缺水区水系统的模拟分析——以上海杨浦区为例

针对雨量丰富的南方地区出现水质型缺水问题,采用系统动力学方法,对其水系统做模拟分析。以上海杨浦区为分析实例,根据其特征设立模型,包括5个子系统、6个调控参数。通过调整调控参数,运行模型得到所需的3种不同方案。在此基础上,找出影响需水系统的主要因素为:水价 、污水治理系数、节水意识、工艺改革。基于三种方案的作用参数和模拟结果,为解决水资源这一"瓶颈"问题,实现杨浦区水系统的供需平衡和区域的协调发展,提出具体的调整政策。其中,该政策的调控参考值 (对应年:1990/1995/2000/2005/2010/2015/2020)为:水价TPW=1.3/2.7/2.9/3.5/4.7/5.2/6.8;污水治理率TRWW=0.73/0.79/0.84/0.85/0.93/0.96/0.97;节水意识为INDEX1=2.5 (2005年后),INDEX2=1.021 (2005年前);工艺改革系数为TRT=1/1.1/1.28/1.35/1.5/1.65/1.66。在实施相应措施的基础上,采用协调发展方案,预测到2020年上海杨浦区总需水量约14.0×10⁹t,而预计工程供水能力可达到约13.9×10⁹t,基本达到水系统的供需平衡,实现区域水资源的协调发展。     

Spatiotemporal evolution and driving factors of global production networks: An analysis based on the input-output technique

Global production networks have become the most important organizational plat-forms for coordinating international production activities,and their evolution patterns pro-foundly affect value distribution across the world.In this study,we shall firstly carry out an in-depth quantitative research to analyze the patterns and evolution of global production networks,using a long time-sequenced multi-region input-output table and the network analysis approach.Then based on the method of value-added decomposition,we will develop an index system to measure the degree of participation of regions in global production net-works.Finally,we will try to identify the factors affecting the degree of participation of coun-tries in global production networks by constructing a regression model.The results show that from 1995 to 2015,the evolution of global production networks measured by input-output linkages experienced four stages:expansion,contraction,re-expansion,and re-contraction.In addition,the core communities of global production networks evolved from two major production communities(Europe and the Americas)to three pillars(Europe,Americas,and Asia)while more segmented communities are mainly affected by geographical proximity.The latter consists of European,North American,South American,African and Asian communities.The evolution of the global production network pattern primarily manifests as a process of cooperation strengthening or weakening among communities,based on changes in the ex-ternal environment and the need for individual development strategies.Meanwhile,the United States,Germany,and the United Kingdom have consistently ranked among the top entities in global production networks,whereas China,Russia,and Southeast Asia have the fastest rises in ranking.In addition,government efficiency,resources endowment,infrastructure conditions and technology levels play important roles in the participation in global production networks.     

基于微博语义分析的重庆主城区风貌感知评价

采用社交网络数据对城市进行感知与评价是一种新的城市感知定量研究方法。本文将新浪微博签到数据作为城市感知的数据来源,通过文本挖掘和语义分析方法,探索用户对重庆主城区城市风貌的感知与评价。针对重庆主城区特色风貌片区,研究形成了签到地图、情绪地图和对象地图。签到地图客观反映重庆主城区新浪微博用户活跃程度的空间分布特征;情绪地图挖掘活跃用户对空间的情绪表达和正负面态度;对象地图解析出现这种签到热力分布和情绪分布的原因,发现引发正负面态度的情绪对象。通过分析用户对规划师所设定的风貌要素载体的典型意见,将要素载体归纳为有感知积极、有感知消极、无感知和有感知未设定4类。今后应进一步从要素识别和价值判断两个方面为规划师塑造和管控城市风貌提供参考意见。     

城市老年人的移动性变化及其对日常生活的影响——基于社区老年人生活历程的叙事分析

就地养老日益受到中国城市老年人的欢迎,其中个体移动性对老年人日常生活尤具重要意义。本文从微观个体的视角出发,运用质性研究方法,选取一对空巢的高龄老年夫妇作为典型案例,对其退休以来的移动性变化与日常生活历程进行叙事分析;以期揭示移动性对老年个体生活的重要意义、移动性的变化特征与日常生活的密切关联,从而为中国城市老年服务与宜老环境建设提供科学支持。结果表明,老年个体移动性具有日常活动空间向外拓展、逐渐向社区及周边收缩、局限于家及住所附近3个阶段;随年龄增长而不断下降的身体机能与健康状况,和家庭因素共同促使老年人移动性与日常生活发生阶段性演变;个人、家庭、所在社区的资源分别构成了各阶段的核心影响因素。个体的移动性空间应成为中国城市宜老社区与环境建设以及老年规划与服务的关键命题。