Identification of flood seasonality using an entropy-based method

Identifying flood seasonality is critical in hydrologic applications as well as water resources management. We develop an entropy-based method (EBM) for identifying flood seasonality and partitioning the entire flood season into multiple sub-seasons. The performance of the proposed EBM is evaluated using a Monte Carlo simulation test and compared with current methods. The Three Gorges Reservoir (TGR) basin in the Yangtze River is selected as a case study to test the applicability of the proposed method. Results of Monte Carlo simulation test demonstrate that the EBM performs better than the probability change-point method and the improved relative frequency method with less bias and higher efficiency. The case study results illustrate that the EBM can appropriately divide the entire flood season of the TGR into pre-flood season (from June 1st to June 20th), main-flood season (from June 21th to September 10th) and post-flood season (from September 11th to September 30th). The flood limited water levels (FLWL) in these three sub-seasons can then be derived, which are 150 m, 145 m and 149 m, respectively. Compared with conventional operation rule, the seasonal FLWL scheme can generate more hydropower (0.93 billion KWh) annually with a reliability of 99.86%. Therefore, it is meaningful to divide the entire flood season into three sub-seasons and apply seasonal FLWL for TGR operation.     

Rapid improvement of PM_(2.5) pollution and associated health benefits in China during 2013–2017

Exposure to fine particulate matter(PM_(2.5)) is known to harm public health.In China,after implementation of aggressive emissions control measures under the Action Plan of Air Pollution Prevention and Control(2013-2017),air quality has significantly improved.In this work,we investigated changes in PM_(2.5) exposure and the associated health impacts in China for the period 2013-2017.We used an optimal estimator of PM_(2.5) combining in-situ observations,satellite measurements,and simulations from a chemical transport model to derive the spatial and temporal variations in PM_(2.5) exposure,and then used welldeveloped exposure-response functions to estimate the premature deaths attributable to PM_(2.5) exposure.We found that national population-weighed annual mean PM_(2.5) concentrations decreased from 67.4μgm~(-3) in 2013 to 45.5μgm~(-3) in 2017(32%reduction).This rapid decrease in PM_(2.5) pollution led to a 14% reduction in premature deaths due to long-term exposure.We estimated that,during 2013-2017,the premature deaths attributable to long-term PM_(2.5) exposure decreased from 1.2 million(95% CI:1.0,1.3;fraction of total mortality:13%) in 2013 to 1.0 million(95% CI:0.9,1.2;10%) in 2017.Despite the rapid decrease in annual mean PM_(2.5) concentrations,health benefits associated with reduced long-term exposure were limited,because for many cities,the PM_(2.5) levels remain at the portion where the exposure-response function is less steeper than that at the lowconcentration end.We also found that the deaths associated with acute exposure decreased by 61% during 2013-2017 due to rapid reduction in the number of heavily polluted days.Our results confirm that clean air policies in China have mitigated the air pollution crisis;however,continuous emissions reduction efforts are required to protect citizens from air pollution.     

机载LiDAR点云密度和插值方法对DEM及地表粗糙度精度影响分析

机载LiDAR点云是获取高质量数字高程模型(Digital Elevation Model, DEM)的主要数据源,而地表粗糙度作为DEM的主要派生产品,在地学研究中发挥了重要作用,但点云密度和插值方法对DEM及地表粗糙度精度影响程度并没有明确结论。为此,本文利用不同地形条件下的林区机载LiDAR点云为实验对象,将原始点云随机缩减为不同的采样密度,利用5种常用插值方法(克里金(Ordinary Kriging, OK),径向基函数(Radial Basis Function, RBF),不规则三角网(Triangulated Irregular Network, TIN),自然邻域(Natural Neighbor, NN)和反距离加权(Inverse Distance Weighting, IDW))构建各个测区不同采样密度条件下的DEM,并通过空间特征和统计特征两方面对DEM及其地表粗糙度精度分析。结果表明:(1) DEM插值算法的精度随点云密度缩减而降低,且数据量缩减至原始数据量的30%后,不同算法精度区别较为明显,其中,RBF和OK精度最优,IDW精度最低;(2) DEM误差与...     

THE PROCESS OF MAKING 3D VECTOR SCENOGRAPH OF ANCIENT BUILDING WITH LARGE QUANTITIES OF DATA

1　ＩｎｔｒｏｄｕｃｔｉｏｎＡｎｃｉｅｎｔｂｕｉｌｄｉｎｇｓ ,ａｓｔｈｅｅｓｓｅｎｃｅｏｆａｎｃｉｅｎｔＣｈｉ ｎｅｓｅｃｕｌｔｕｒｅ ,ｃｈａｒａｃｔｅｒｉｚｅｄｂｙｉｔｓｃｏｍｐｌｅｘａｎｄａｎ ｔｉｑｕｅｓｈａｐｅ ,ｄｅｌｉｃａｔｅｓｔｒｕｃｔｕｒｅ ,ｃｏｍｐａｃｔｃｏｍｂｉｎａｔｉｏｎａｎｄ ｇｒａｃｅｆｕｌｓｃｕｌｐｔｕｒｅ ,ａｒｅａｐｐｒｅｃｉａｔｅｄ ｇｌｏｂａｌｌｙ .Ｓｏｍｅａｎｃｉｅｎｔｂｕｉｌｄｉｎｇｓｍａｄｅｏｆｗｏｏｄｅｎｄｕｒｅｌｏｎｇｂｅｃａｕｓｅｏｆｉｔｓｓｏｌｉｄｓｔｒ…     

宜昌站1882-2007年径流变化规律分析

以长江流域宜昌站1882-2007年的天然径流序列为基础数据,采用Mann-Kendall检验法和小波分析等统计方法,对径流序列各年代年内变化和年际分配变化进行了分析.结果表明,年内变化中,宜昌站径流分配不均匀,各个年代径流量集中在汛期;不均匀性和集中程度以20世纪20-50年代最明显,21世纪初最不明显,其他年份均介于二者之间,差别不大.在年际变化中,宜昌站多年径流量呈现减少的趋势,但并不显著;1935年左右为径流突变年份,径流量由突变前的14432 m3/s减少到突变后的13471 m3/s,减少了961 m3/s;多年径流量均存在12a和27 a的变化周期.     

大型木造建筑物的计算机仿真和质量控制

利用传统测量方法和现代测绘技术相结合,对大型木造建筑物进行计算机三维模型构造并以此对整个重建工程进行测量监控,也对一些新的设备和技术在占建筑领域的应用作了有益的尝试。结果表明,在占文物古建筑维护和重建过程中,用计算机三维仿真来保存完整数据资料和对施工过程进行质最监控是一种合适的方法。     

Sensitivity Experiments on the Poleward Shift of Tropical Cyclones over the Western North Pacific under Warming Ocean Conditions

Recent studies found that in the context of global warming, the observed tropical cyclones (TCs) exhibit significant poleward migration trend in terms of the mean latitude where TCs reach their lifetime-maximum intensity in the western North Pacific (WNP). This poleward migration of TC tracks can be attributed to not only anthropogenic forcing (e.g., continuous increase of sea surface temperature (SST)), but also impacts of other factors (e.g., natural variability). In the present study, to eliminate the impacts of other factors and thus focus on the impact of unvaried SST on climatological WNP TC tracks, the mesoscale Weather Research and Forecasting (WRF) model is used to conduct a suite of idealized sensitivity experiments with increased SST. Comparisons among the results of these experiments show the possible changes in climatological TC track, TC track density, and types of TC track in the context of SST increase. The results demonstrate that under the warmer SST conditions, the climatological mean TC track systematically shifts poleward significantly in the WNP, which is consistent with the previous studies. Meanwhile, the ocean warming also leads to the decreased (increased) destructive potential of TCs in low (middle) latitudes, and thus northward migration of the region where TCs have the largest impact. Further results imply the possibility that under the ocean warming, the percentage of TCs with westward/northwestward tracks decreases/increases distinctly.     

Uncertainty analysis of groundwater model based on data assimilation北大核心CSCD

黑河流域中下游地下水系统受上游冰冻圈融水和降雨的补给,由气候变暖导致的冰冻圈萎缩致使中下游地下水系统的稳定性面临更多的风险。地下水模型是地下水系统稳定性评估的有效手段,但是地下水模型参数往往存在较大的不确定性。为此,本文提出了基于数据同化算法的不确定性分析方法,通过包含观测资料信息减小模型不确定性。采用所提方法分析了(基于MODFLOW构建)黑河流域中游地下水模型中13个参数的不确定性,讨论了算法超参数的影响及其最优取值,分析了地下水模型参数的不确定性。实验结果证明数据同化算法可有效减小地下水模型参数的不确定性,观测资料的种类与数量对参数不确定性的减小起到重要作用;不同地下水模型参数的不确定性不同,地表水与地下水相互作用频繁的区域参数不确定性较大;含水层渗透系数、含水层给水度以及灌溉回流系数对模型输出的地下水位输出影响显著,河床水力传导系数对模型输出的河流流量影响较大。本研究将为地下水研究提供更加可靠的模型方法,为西北内流区地下水哺育的绿洲生态系统稳定可持续研究提供重要支撑。     

中国北方沙尘气溶胶对云和降水影响的数值模拟研究

已有的研究表明中国北方千旱半干旱地区是对流层沙尘气溶胶的主要来源之一,对当地乃至全球气候都有重要的意义.利用数值模拟研究方法探讨不同干燥程度的大气背景环境下,沙尘气溶胶数浓度对混合云形成和发展的可能影响,并采用析因试验讨论了主次影响因素.结果表明:沙尘气溶胶的增加导致降水减少、延长了云在空中存在的时间,改变了云的空间结构和微观结构.析因分析表明干旱半干旱气候背景条件下,混合云的累计降水量对沙尘气溶胶数浓度变化的敏感性要高于对大气环境湿度的敏感性;沙尘气溶胶数浓度增加导致云累计降水量的减少;沙尘气溶胶数浓度和大气环境湿度对云的累计降水量的影响是复杂的,研究结果可以用于指导降水预报业务.     

金沙江下游梯级水库运行期设计洪水及汛控水位

研究探讨梯级水库运行期设计洪水计算理论和方法,实现防洪和发电效益最大化。采用t-Copula函数建立各分区洪水的联合分布,通过蒙特卡罗法和遗传算法(GA)推求金沙江下游梯级水库的最可能地区组成;分析计算各水库运行期的设计洪水及汛控水位。结果表明:①最可能地区组成结果合理可靠,可为梯级水库运行期设计洪水的分析计算提供依据;②金沙江下游梯级水库受上游水库调蓄影响显著,向家坝水库1000年一遇设计洪峰15400m^3/s(35%),3d、7d和30d洪量的削减量(削减率)分别为35.6亿m^3(33%)、70.2亿m^3(30%)和85.0亿m^3(11%);③在不降低防洪标准的前提下,下游各水库在运行期汛控水位相比汛限水位可适当抬高,白鹤滩、溪洛渡和向家坝水库的汛控水位(汛限水位)分别为788.82m(785m)、570.67m(560m)和371.36m(370m),汛期年均发电量分别增加2.1%、6.1%和1.4%,年增发电量17.1亿kW·h。