Exploring the stemflow dynamics and driving factors at both inter- and intra-event scales in a typical subtropical deciduous forest     

Haixia Zhang  Congsheng Fu  Aimin Liao  Can Zhang  Jiufu Liu  Niu Wang  Bin He 《水文研究》2021,35(3):e14091

Numerous efforts have been made to understand stemflow dynamics under different types of vegetation at the inter-event scale, but few studies have explored the stemflow characteristics and corresponding influencing factors at the intra-event scale. An in-depth investigation of the inter- and intra-event dynamics of stemflow is important for understanding the ecohydrological processes in forest ecosystems. In this study, stemflow volume (F_V), stemflow funnelling ratio (F_R), and stemflow ratio (F_%) from Quercus acutissima and Broussonetia papyrifera trees were measured at both inter- and intra-event scales in a subtropical deciduous forest, and the driving factors, including tree species and meteorological factors were further explored. Specifically, the F_V, F_R and F_% of Q. acutissima (52.3 L, 47.2, 9.6%) were lower than those of B. papyrifera (85.1 L, 91.2, 12.4%). The effect of tree species on F_V and F_% was more obvious under low intensity rainfall types. At the inter-event scale, F_V had a strong positive linear correlation with rainfall amount (G_P) and event duration (D_E) for both tree species, whereas F_R and F_% had a positive logarithmic correlation with G_P and D_E only under high-intensity, short-duration rainfall type. F_R and F_% were mainly affected by wind speed and the maximum 30-min rainfall intensity under low-intensity, long-duration rainfall type. At the intra-event scale, for both tree species, the mean lag time between the start of rainfall and stemflow was the shortest under high-intensity, short-duration rainfall type, while the mean duration and amount of stemflow after rain cessation were the greatest under high-amount, long-duration rainfall type. The relationship between stemflow intensity and rainfall intensity at the 5-min interval scale also depended greatly on rainfall type. These findings can help clarify stemflow dynamics and driving factors at both inter- and intra-event scales, and also provide abundant data and parameters for ecohydrological simulations in subtropical forests.  相似文献   

Numerical Simulation of Magnetic Reconnection Driven by the Laser Helmholtz Capacitor-coil Targets     

XU Shan-shan  MEI Zhi-xing  ZHONG Jia-yong  LIN Jun 《Chinese Astronomy and Astrophysics》2021,45(2):131-146

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A two-layer model for studying 2D dissolved pollutant runoff over impermeable surfaces     

Taotao Zhang  Yang Xiao  Dongfang Liang  Hongwu Tang  Junzeng Xu  Saiyu Yuan  Nairu Wang  Bin Luan 《水文研究》2021,35(5):e14152

Dissolved pollutants in stormwater are a main contributor to water pollution in urban environments. However, many existing transport models are semi-empirical and only consider one-dimensional flows, which limit their predictive capacity. Combining the shallow water and the advection–diffusion equations, a two-dimensional physically based model is developed for dissolved pollutant transport by adopting the concept of a ‘control layer’. A series of laboratory experiments has been conducted to validate the proposed model, taking into account the effects of buildings and intermittent rainfalls. The predictions are found to be in good agreement with experimental observations, which supports the assumption that the depth of the control layer is constant. Based on the validated model, a parametric study is conducted, focusing on the characteristics of the pollutant distribution and transport rate over the depth. The hyetograph, including the intensity, duration and intermittency, of rainfall event has a significant influence on the pollutant transport rates. The depth of the control layer, rainfall intensity, surface roughness and area length are dominant factors that affect the dissolved pollutant transport. Finally, several perspectives of the new pollutant transport model are discussed. This study contributes to an in-depth understanding of the dissolved pollutant transport processes on impermeable surfaces and urban stormwater management.  相似文献   

Sentinel-2卫星落叶松林龄信息反演   总被引：1，自引：0，他引：1  

唐少飞  田庆久  徐凯健  徐念旭  岳继博 《遥感学报》2020,24(12):1511-1524

林龄结构信息能够有效反映区域森林群落不同生长阶段的固碳能力，对于评估森林生态系统的健康状况具有重要意义。本研究以中国温带典型优势树种落叶松林为研究对象，分别选择其芽萌动期、展叶期和落叶期时段的Sentinel-2影像，采用多元线性回归（MLR）、随机森林（RF）、支持向量机回归（SVR）、前馈反向传播神经网络（BP）以及多元自适应回归样条（MARS）等5种方法依次构建落叶松林龄反演模型。通过相关性分析首先确定最佳遥感反演物候期，并在此基础上根据相关性差异筛选出5个最优特征变量用于模型反演，分别为冠层含水量（CWC），归一化水体指数（NDWI），叶面积指数（LAI），光合有效辐射吸收率（FAPAR）和植被覆盖度（FVC）。研究结果表明，展叶期为落叶松林最佳遥感反演物候期。除植被衰减指数（PSRI）以及落叶期的NDVI、RVI外，落叶松林龄与各指标之间均呈负相关关系，其中与冠层含水量（CWC）的相关性最高，pearson相关系数达到-0.74（p<0.01）。此外，不同模型反演结果表明，随机森林模型（RF）为最佳落叶松林龄估测模型，其平均决定系数R²和平均均方根误差RMSE分别为0.89和2.91 a；多元线性回归模型（MLR）的林龄估测结果最差，其平均决定系数R²和平均均方根误差RMSE仅为0.57和5.69 a，非线性模型能更好的解释林龄与建模变量之间的关系。  相似文献   

香坊老工业区搬迁改造监测分析     

李晶晶  罗研  张滨 《测绘与空间地理信息》2020,(2):182-184,188

利用地理信息技术及遥感监测方法,监测香坊老工业区搬迁改造试点进展情况,主要针对搬迁改造过程中地表覆盖、用地性质、空气质量变化情况,开展综合统计分析,客观评价香坊老工业搬迁改造实施成效。  相似文献   

大西安地区土地利用类型时空演变分析          下载免费PDF全文

马新萍  韩申山  王磊  王建兴  许晓婷 《干旱区地理》2020,43(2):499-507

通过多种方法分析大西安地区土地利用类型演变特征、空间变化特征及其影响因素，旨在为大西安地区土地利用优化发展提供科学基础。在GIS和RS技术的支持下，对区域1996年、2006年、2016年3期LANDSAT TM（OLI）遥感影像进行解译，采用土地利用转移矩阵和土地利用变化模型对大西安1996 年以来土地利用类型和土地覆被时空动态变化进行量化分析，结果表明：（1） 大西安近20 a来建设用地面积不断增加，耕地、林业用地面积总体减少，草地小幅增加，水域略有萎缩，各地类间相互转换频繁。（2） 土地利用综合程度较高且不断加强，土地利用结构趋于均衡。（3） 空间变化上，土地利用变化区域差异显著，建设用地、耕地、林业用地重心转移的速度呈现出先快后慢的阶段性特征。（4） 综合相关文献，大西安地区土地利用变化的驱动因素主要为政策因素。论文从时空变化角度首次提出大西安地区的土地利用演变规律，该结果可为大西安地区发展过程中的土地优化提供科学基础。  相似文献   

基于PCA-TOPSIS的重庆市县域经济密度综合测度及时空演变          下载免费PDF全文

张彬  谢贤健  杨联安  郭金铭 《干旱区地理》2020,43(2):546-556

经济密度是衡量区域经济发展水平和聚集程度的重要指标之一。以重庆市38个县（区）所辖范围为研究区，建立了人均和地均相结合的综合测度指标体系，采用主成分分析确定指标权重，将PCA TOPSIS评价法运用到经济密度综合测度中，依据测度对象与最优值的相对接近程度，综合测度1997年、2001年、2006年和2013年重庆市县域经济密度，获得各个时间断面经济密度综合指数及其排名。通过利用ArcGIS制图功能绘制重庆市经济密度等级分布图，揭示其空间分异演变规律，利用Moran’s I，LISA和热点分析分别探索了县域经济密度的全局和局部空间自相关及其时空演变规律，并讨论影响经济密度高低的主要因素。通过对县域经济密度的综合测度及时空演变的探究，为实现城市科学定位和制定中长期发展战略提供科学依据。  相似文献   

德令哈13.7m望远镜接收机抗射频干扰研究     

李振强  李积斌  张旭国  单文磊  徐烨  左营喜  张海龙  金风娟  孙继先  逯登荣  巨秉刚 《天文学报》2019,60(3):62-76

在天文观测中,射频干扰会造成假谱,降低数据的可靠性和有效性.射频干扰消减旨在减少干扰信号对射电天文观测的影响,包含器件方面的技术革新和数据处理领域的方法研究.针对德令哈13.7 m望远镜接收机中频部分引入的射频干扰,通过优化中频器件的抗射频干扰能力,提高了接收机的整体抗射频干扰能力,以主动消除方法来减少射频干扰耦合到接收机内部.分析了接收机干扰的传输路径,提出了器件射频干扰的直接耦合系数和器件射频干扰的系统耦合系数的概念,为定位干扰敏感器件并量化干扰引入比重提供了基础.经过抗射频干扰优化后,接收机抗干扰能力改善30 dB左右,望远镜的天文观测效率提高10%以上.  相似文献   

High-P granulites of the Songshugou area (Qinling Orogen,east-central China): Petrography,phase relations,and U/Pb zircon geochronology     

Thomas Bader  Lifei Zhang  Xiaowei Li  Bin Xia  Leander Franz  Christian de Capitani  Qingyun Li 《Journal of Metamorphic Geology》2020,38(4):421-450

High-pressure (HP) granulites provide telling records of mineral reactions at upper mantle to lower crustal levels and key information on the fate of material in subduction systems. The latter especially applies when they abut eclogite and mantle dunite because such rock associations are crucial for understanding the incompletely known processes at the interface of converging plates. A continental arc, active c. 520–395 Ma ago, formed an enigmatic example of such a rock association in the Songshugou area, Qinling Orogen. To unravel the juxtaposition of the distinct rocks, this study combines petrography, phase equilibria modelling, conventional thermobarometry, and zircon U–Th–Pb–Ti–REE analysis. Two mafic HP granulites, which contain the mineral assemblages garnet–clinopyroxene–plagioclase–rutile–mesoperthite–quartz and garnet–clinopyroxene–plagioclase–rutile, experienced peak metamorphic conditions of ≤1.4 GPa, 860°C and ~1.3 GPa, ≥910°C, respectively. During decompression and cooling, at 489 ± 4 Ma, amphibole lamellae unmixed from a clinopyroxene solid solution and orthopyroxene in part replaced garnet. A felsic HP granulite shows equilibration of garnet, perthite, antiperthite, kyanite, quartz, and rutile at 810–860°C, ~1.2 GPa, sillimanite growth during decompression, and upper amphibolite facies cooling at 510 ± 4 Ma. Though the thermobarometric data are just within the methodological errors, the U/Pb zircon ages imply the HP granulites did not evolve coherently. The HP granulites either represent foundered lower arc crust or originated from subduction erosion because their geochemistry is indistinguishable from that of the hanging-wall plate. Published and new pressure–temperature–time–deformation paths converge at ~710°C, ~0.9 GPa, and ≲470 Ma, implying exhumation tectonics juxtaposed the HP granulites with a mélange of eclogite and mantle dunite at lower crustal levels. This study highlights that lower arc crust can comprise material of diverse evolution.  相似文献   

顾及基准站坐标动态特性与稳定性的区域框架构建     

蒋光伟  王斌  王延伟  李康  孙洋洋 《地球物理学进展》2020,(1):8-15

基准站受构造运动与非线性因素的影响,如何构建高精度、现势性强的精细区域框架是位置服务与形变分析的的关键.笔者提出顾及基准站坐标动态特性与稳定性的区域框架构建方法.以我国西部与东部某城市的多年连续运行基准站数据为例进行试算比对,试验结果表明:该方法是可行的,较好地顾及了基准站的坐标特性与非线性影响,考虑了基准站的垂直运动规律,可构建高精度的区域基准,可发现区域基准的微动态变化.  相似文献