Development of climate change projections for small watersheds using multi-model ensemble simulation and stochastic weather generation

Regional climate models (RCMs) have been increasingly used for climate change studies at the watershed scale. However, their performance is strongly dependent upon their driving conditions, internal parameterizations and domain configurations. Also, the spatial resolution of RCMs often exceeds the scales of small watersheds. This study developed a two-step downscaling method to generate climate change projections for small watersheds through combining a weighted multi-RCM ensemble and a stochastic weather generator. The ensemble was built on a set of five model performance metrics and generated regional patterns of climate change as monthly shift terms. The stochastic weather generator then incorporated these shift terms into observed climate normals and produced synthetic future weather series at the watershed scale. This method was applied to the Assiniboia area in southern Saskatchewan, Canada. The ensemble led to reduced biases in temperature and precipitation projections through properly emphasizing models with good performance. Projection of precipitation occurrence was particularly improved through introducing a weight-based probability threshold. The ensemble-derived climate change scenario was well reproduced as local daily weather series by the stochastic weather generator. The proposed combination of dynamical downscaling and statistical downscaling can improve the reliability and resolution of future climate projection for small prairie watersheds. It is also an efficient solution to produce alternative series of daily weather conditions that are important inputs for examining watershed responses to climate change and associated uncertainties.     

以SRTM-DEM为控制的光学卫星遥感立体影像正射纠正

针对全球测图缺少统一的控制基准的问题,提出了利用SRTM-DEM作为控制基准,对光学卫星遥感影像进行正射纠正的方法。首先,对光学卫星影像构建的立体影像对进行自由网平差并制作DEM;然后,以SRTM-DEM作为控制,将DEM作为单元模型,进行独立模型法DEM区域网平差,获得单元模型的定向参数;最后,改正立体影像的成像几何模型参数,进行正射纠正。选取湖北咸宁和江西某地两个测区的资源三号数据进行试验,试验结果表明,资源三号正视全色影像的平面定向精度由12.93像素提高到6.85像素。     

非线性中立型时滞微分方程解的振动性

本文研究几类非线性中立型时滞微分方程解的振动性质 ,利用 Riccati不等式和某个不等式得到了保证方程振动的充分条件     

北京一次极端雨雪天气异常诊断分析

2020年2月13—14日北京地区出现一次极端雨雪天气过程,利用EC再分析数据、风廓线雷达、气候资料等,采用诊断分析、风廓线产品反演、气候异常分析等方法,对这次伴有复杂相态转换、对流、累计降水量破历史同期极值的极端雨雪天气过程进行分析和异常诊断,结果表明：①大尺度低涡、高\低空急流、锋面等天气系统为降水提供良好的背景条件。②河北中部的中尺度涡旋,是这次极端雨雪天气的重要成因之一。③对流活动的参与提高了降水效率,致使过程累计降水量进一步加大。④850 hPa切变线北侧强盛的偏东气流,在动力抬升和水汽输送及辐合中发挥重要作用。⑤-8～-20 ℃层云冰含量低,且0 ℃层高度超过700 m是造成北京平原地区相态转换时间延迟的直接原因。⑥边界层回流冷空气由平原东部进入北京,是雨雪相态转换由东向西发生的根本原因。⑦极端的水汽通量辐合异常,是此次天气过程累计雨量突破同期历史极值的重要原因之一。     

瘤背石磺体腔细胞分类、免疫相关酶特性及初步转录组学分析

瘤背石磺(Onchidium struma)广泛分布于潮间带和潮下带,是海洋生物向陆地生物辐射进化的重要代表,也是环境监测的指示生物.为丰富瘤背石磺的基础免疫学资料,本文研究了瘤背石磺体腔细胞的类别、细胞密度和体腔液免疫相关酶活性,并通过RNA-Seq测序获得体腔细胞转录本,进行生物信息学分析.结果表明,瘤背石磺主要有...     

Landscape Dynamics and Driving Factors in Da＇an County of Jilin Province in Northeast China During 1956-2000

The landscape pattern of Da＇an County, Northeast China has undergone significant changes since the 1950s as a result of climatic change and human activities. The aim of this paper is to quantitatively study landscape pattern and its spatial dynamics of Da＇an County at the landscape level over the nearly 50-year span. Patch dynamics were examined according to land use and land cover change processes built from a series of images, as well as topographic maps, and temporal patterns built from landscape pattern metrics. The transition matrix of landscape patch types and changes of various landscape metrics were applied. The results showed that, from 1956 to 2000, the landscape within the study area had undertaken a complicated evolution in landscape structure and composition. The outstanding characteristic is that saline-alkali land increased and grassland decreased. As some smaller patches amalgamated, the heterogeneity of patch decreased. All those changes were the synthetic result of both climatic and anthropogenic influences, but the predominant factor was different in different parts. In the southern part of the study area, the landscape pattern changes resulted from the modification of climate obviously, while in the northern part, the landscape pattern changes were mainly caused by human activities, such as the conversion between farmland and saline-alkali land. This phenomenon showed that human activities played more important role in the north than in the south of Da＇an County.     

区域创新网络模式研究——以长三角城市群为例

网络范式的兴起赋予城市创新模式新的内涵,引起了经济地理学者对不同空间尺度知识流动和创新联系的关注。基于网络视角,以中国知识产权局2014年长三角城市群26个地级市合作发明专利信息为原始数据,借助Ucinet、ArcGIS等分析工具,从本地和跨界多维空间尺度,刻画长三角城市群创新网络结构,测度城市创新网络地位,评价城市创新能力,进而对城市创新模式进行划分。研究表明：①研发密集的大型国有企业、中外合资企业和知名的理工科院校具有较高的知识生产能力,成为长三角城市群创新合作优先链接主体;②长三角城市群重视外部知识获取,跨界网络成为重要的创新合作途径,地理距离对创新合作空间载体选择的制约减弱;③创新网络位置影响知识获取和城市创新,网络视角下的长三角城市群呈现四类创新模式,密集的“本地—跨界”创新网络有助于城市创新。研究结论对长三角城市群不同类型创新模式的优化升级具有一定的参考价值。     

Early Paleozoic subduction of the Paleo-Asian Ocean: Geochronological and geochemical evidence from the Dashizhai basalts,Inner Mongolia

Zircon U-Pb results of basalt from the Dashizhai Town in Inner Mongolia, NE China, shows that the basaltic lava was erupted at 439±3 Ma, much older than the “Permian basalts” as previously thought. These rocks show arc-type trace element patterns (i.e., Nb-Ta depletion and light REE and large ion lithophile element enrichment) and unradiogenic Sr and highly radiogenic Nd and Hf isotope compositions. They can be subdivided into two petrogenetic groups: Group 1 basalts have relatively high TiO₂, MgO and compatible elements and low Sr and Th, characterized by mid-oceanic ridge basalt (MORB)-type Sr-Nd-Hf isotope compositions (⁸⁷Sr/⁸⁶Sr(i)=0.7028−0.7032, ε_Nd(t)=+9.8−+11.2, ε_Hf(t)=+16.1−+18.4). Group 2 has lower TiO₂, MgO and compatible elements and higher Sr and Th, and relatively evolved Sr-Nd-Hf isotope compositions (⁸⁷Sr/⁸⁶Sr(i)=0.7037−0.7038, ε_Nd(t)=+5.7−+7.3, ε_Hf(t)=+12.6−+13.0). Both groups were interpreted as melts derived from a metasomatized mantle wedge formed during the subduction of Paleo-Asian Ocean. The mantle source for Group 1 was probably a highly isotopically depleted oceanic mantle modified by predominant slab fluids; whereas subducted sediments had an important contribution to the melting source for Group 2. The petrogenesis of the Dashizhai basalts provides clear evidence for early Paleozoic subduction of the Paleo-Asian Ocean, and the highly radiogenic Nd and Hf compositions in these rocks suggest that these lavas and their possible intrusive counterparts were one of the important components for Phanerozoic crustal growth. Our and previous studies on the “Dashizhai Formation” volcanic rocks yield an unrealistic eruption range of 440-270 Ma for different rock types, we thus advise to disassemble the previously defined “Dashizhai Formation” into multiple lithologic units and to reinterpret the spatial and temporal distributions of different volcano-sedimentary associations. Supported by National Basic Research Program of China (Grant No. 2006CB403504)     

甘肃省舟曲特大泥石流的遥感影像特征及古泥石流遥感识别的地质意义

2010年舟曲特大泥石流是舟曲地区第四纪以来泥石流最新暴发期内强烈活动的体现,所造成的人员伤亡及财产损失堪称世界泥石流灾害史之最。准确分析该地区泥石流的空间分布规律及预测未来泥石流暴发时间可为泥石流的防灾救灾提供科学的依据,其首要任务就是利用一种先进技术对不同时期的泥石流堆积物的空间分布进行快速、准确的识别。遥感技术具有数据获取量大、空间分辨率高及快速等方面的独特优势,可在舟曲特大泥石流及不同时期古泥石流堆积物识别中发挥重要作用。在高分辨率的航空遥感影像上,舟曲特大泥石流具有明显的光谱特征,可用于准确圈定泥石流灾害的范围; 泥石流堆积物在沟谷两侧形成的侧碛堤及在堆积区末端形成的扇形地等形态特征也是识别泥石流的另一个重要标志。舟曲县城东南瓦厂村南及马莲坪村西南白龙江支流沟中的垄岗状堆积物和沟口处的扇形地堆积体在光学遥感影像上具有典型的古泥石流堆积的形态特征,雷达遥感的后向散射系数对比分析和对堆积物剖面的沉积特征分析也证明古泥石流的存在。研究结果表明,通过多期次、多空间分布的现代和古泥石流的对比,不仅可以揭示舟曲地区第四纪以来泥石流发育历史并间接反映地质尺度上气候变化特点,还可为未来泥石流的易发性分析提供数据支撑,因此泥石流堆积物的遥感直接识别具有重要的地质意义。