Have applications of continuous rainfall–runoff simulation realized the vision for process‐based flood frequency analysis?

Keith Beven was amongst the first to propose and demonstrate a combination of conceptual rainfall–runoff modelling and stochastically generated rainfall data in what is known as the ‘continuous simulation’ approach for flood frequency analysis. The motivations included the potential to establish better links with physical processes and to avoid restrictive assumptions inherent in existing methods applied in design flood studies. Subsequently, attempts have been made to establish continuous simulation as a routine method for flood frequency analysis, particularly in the UK. The approach has not been adopted universally, but numerous studies have benefitted from applications of continuous simulation methods. This paper asks whether industry has yet realized the vision of the pioneering research by Beven and others. It reviews the generic methodology and illustrates applications of the original vision for a more physically realistic approach to flood frequency analysis through a set of practical case studies, highlighting why continuous simulation was useful and appropriate in each case. The case studies illustrate how continuous simulation has helped to offer users of flood frequency analysis more confidence about model results by avoiding (or exposing) bad assumptions relating to catchment heterogeneity, inappropriateness of assumptions made in (UK) industry‐standard design event flood estimation methods, and the representation of engineered or natural dynamic controls on flood flows. By implementing the vision for physically realistic analysis of flood frequency through continuous simulation, each of these examples illustrates how more relevant and improved information was provided for flood risk decision‐making than would have been possible using standard methods. They further demonstrate that integrating engineered infrastructure into flood frequency analysis and assessment of environmental change are also significant motivations for adopting the continuous simulation approach in practice. Copyright © 2016 John Wiley & Sons, Ltd.     

Probability distribution type of Canadian annual minimum streamflow / Type de distribution de probabilité du débit minimum annuel au Canada

Abstract

The method of L-moment ratio diagrams along with the averaged weighted distance (AWD) is applied to identify a probability distribution of annual minimum streamflow, namely annual minimum daily streamflow in 11 climatic regions of Canada. Across the entire country, the Pearson type III probability distribution is an acceptable distribution for describing annual minimum streamflow with the 3-parameter lognormal and log Pearson type III distributions as potential candidates. Some minor differences in the probability distribution type among different climatic regions are also observed, which may be taken into account in the selection of the distribution type of annual minimum streamflow.     

Trends in frequency of precipitation extremes in the Yangtze River basin,China: 1960–2003 / Tendances d'évolution de la fréquence des précipitations extrêmes entre 1960 et 2003 dans le bassin versant du Fleuve Yangtze (Chine)

Abstract

The spatial distribution and trends in the frequency of precipitation extremes over the last 44 years (1960–2003), especially since 1990, have been analysed using daily precipitation data from 147 stations in the Yangtze River basin. The research results are as follows: (1) The 15 mm precipitation isohyet approximately divides the precipitation extremes (corresponding to the 95th percentile) of the stations in the middle and lower Yangtze reaches (higher) from those of the upper Yangtze reaches (lower). Also the starting time of the precipitation extremes in the middle and lower Yangtze reaches is earlier than of those in the upper Yangtze reaches. Precipitation extremes are concentrated mostly in June in the middle and lower Yangtze reaches, and July in the upper Yangtze reaches. (2) During the period 1960–2003, the first two decades had fewer precipitation extremes than the last two decades. There have been significant increasing trends and step changes in frequency of annual total precipitation extremes and precipitation extremes with a 1–5 day gap in the middle and lower Yangtze reaches. Precipitation extremes occur more frequently in shorter periods, separated by a few days. Precipitation extremes are also becoming more concentrated in the month with the highest frequency of extremes (June) in the middle and lower Yangtze reaches. In the upper Yangtze reaches, there is an upward tendency of extreme events in June. Increasing precipitation extremes in June for both the middle and lower, and the upper Yangtze reaches will increase the probability of flooding if the observed trends of the last 40 years continue into the future.     

A multimodel assessment of the climate change effect on the drought severity–duration–frequency relationship

In this study, the patterns of past and future drought occurrences in the Seoul region were analysed using observed historical data from the Seoul weather station located in the Korean Peninsula and four different types of general circulation models (GCMs), namely, GFDL:CM2_1, CONS:ECHO‐G, MRI:CGCM2_3_2 and UKMO:HADGEM1. To analyse statistical properties such as drought frequency duration and return period, the Standardized Precipitation Index was used to derive the severity–duration–frequency (SDF) curve from the drought frequency analysis. In addition, a drought spell analysis was conducted to estimate the frequency and change of drought duration for each drought classification. The results of the analysis suggested a decrease in the frequency of mild droughts and an increase in the frequency of severe and extreme droughts in the future. Furthermore, the average duration of droughts is expected to increase. A comparison of the SDF relationship derived from the observed data with that derived via the GCMs indicated that the drought severity for each return period was reduced as drought duration increased and that the drought severity derived from the GCMs was severer than the severity obtained using the observed data for the same duration and return period. Furthermore, among the four types of GCMs used in this study, the MRI model predicted the most severe future drought for the Seoul region, and the SDF curve derived using the MRI model also resulted in the highest degree of drought severity compared with the other GCMs. Copyright © 2012 John Wiley & Sons, Ltd.     

卫星导航接收机中锁频环的两种实现方式

对卫星导航接收机中的锁频环进行了研究，主要涉及锁频环的鉴别器算法、环路调节的两种方式，并对这两种实现方式作了仿真。     

基于多源数据的北疆一次持续性浓雾天气过程的演变特征

利用常规高空地面、机场跑道自动观测系统(AWOS)、微波辐射计及FY4A新一代静止气象卫星等资料对2019年12月9～13日发生于北疆沿天山一带的一次持续性浓雾天气进行观测特征及演变分析，结果表明：（1）此次大雾天气过程是发生在500 hPa高空脊区控制，低层不断有暖平流东伸，地面位于蒙古冷高压后部均压场的大尺度环流背景下。（2）大雾发生前，地面明显升温有利于地表融雪、水汽蒸发，这为浓雾的形成和维持提供有利的水汽条件。浓雾维持期间，地面风速维持1 m.s-1左右的弱风场，温度露点差≤2℃，空气接近饱和，准噶尔盆地低洼地形均为浓雾维持提供有力环境条件。浓雾消散期间，风速增大，急剧降温，快速增湿，有利于雾滴凝结为米雪，使得浓雾消散。（3）Brunt-Vaisala（布伦特-维萨拉）指数能较好的反映浓雾期间边界层稳定度，并能提炼出相关稳定度阈值。浓雾期间相对湿度≥85%高度层主要集中在100米以下的贴地层，持续深厚的湿度层为浓雾形成和持续提供较好水汽条件，大雾期间强逆温层顶主要维持在600 m高度，当逆温层顶高度抬升时，有利于雾滴粒子、水汽粒子向上扩散，能见度好转。（4）FY4A卫星的多通道可见光及红外通道差图像能较好的监视白天及夜间大雾的形成、维持及生消变化，对于业务中短时临近预报有较好的帮助。     

SSR改正数更新频率及中断时间间隔对实时PPP的影响分析

实验模拟服务器端不同更新频率的SSR改正数对实时精密单点定位的影响,以及客户端改正数中断时长对实时精密单点定位的影响。结果表明,服务器端SSR改正数的播发频率控制在30 s以内可获得cm级定位精度;客户端的SSR改正数中断在150 s之内可获得cm级定位精度,改正数中断200 s可获得20 cm的定位精度,改正数中断300 s可获得亚m级定位精度。     

关于煤炭三维地震勘探发展的几点思考

根据中国煤炭地震勘探技术发展现状及趋势,提出了三维地震勘探技术今后应重点关注及开展研究的几个问题.提高地震勘探分辨率,首先要提高地震勘探反射波的频率,其次可考虑激发和利用低速波.采用小网格采集技术有利于小构造识别,使用该技术要考虑：一是目标地质体的大小尺度,二是针对倾斜层的最高无混叠频率,三是横向分辨率.利用多次覆盖技术提高地震波信噪比,针对地层倾角大、构造复杂地区,应使用叠前深度偏移处理技术.为提高矿藏及其构造的精细刻画与描述,改善成像质量,应加强开展单点地震勘探高密度采集技术的应用.     

Evidence of nonlinear site response in HVSR from SMART1 (Taiwan) data

Deamplification of strong motion and the increase of the effective period of soil deposits are typical nonlinear effects; we seek them in SMART1-array data by applying the horizontal-to-vertical spectral ratio (HVSR) technique. The recordings, from four soil and one rock stations, represent 23 earthquakes (M_L 4.9–7.0); PGA varies between 20–260 cm/s². For each station, mean HVSR curves are calculated for two PGA ranges: <75 cm/s² and >100 cm/s² (weak and strong motion). At the soil stations, the “weak” (linear) and “strong” (nonlinear) responses are significantly different. Below 1–1.8 Hz, the nonlinear response exceeds the linear one. Above 2 Hz, the nonlinear response drops below the linear one and above 4–6 Hz below unity (deamplification). From 10 to 16 Hz, the two responses converge. One soil site shows significant negative correlation between resonance frequency and ground acceleration. Such behaviour agrees with other empirical studies and theoretical predictions. Our results imply that the HVSR technique is sensitive to ground-motion intensity and can be used to detect and study nonlinear site response.     

钻孔倾斜仪高频实验观测数据的初步分析

利用测震数采器对昌平台CZB钻孔倾斜仪开展了100次/秒的高频采集实验,记录到了可靠的观测资料,其中蕴含的地震信息也更加丰富。同时利用十三陵台测震资料与昌平台钻孔倾斜高频观测资料进行对比分析,结果表明:两种仪器都记录到了地震波响应,但由于频响特性差异,钻孔倾斜仪记录的地震波所对应的P波震相较弱;通过频谱分析估计钻孔倾斜仪的频响偏低频,其频率上限大致在0.1Hz以内;对于一个近地震事件,钻孔倾斜仪的响应表现出与测震仪完全不一样的形态,其低频响应明显优于高频响应;对于远震,随着震中距的增加,两者响应特性逐渐趋于一致。