基于随机暴雨移置方法的城市设计暴雨分析

城市地区暴雨洪灾发生频繁，合理计算设计暴雨是解决城市洪涝的重要前提。采用随机暴雨移置方法（Stochastic Storm Transposition，SST），设定暴雨移置区并提取出暴雨目录，通过区域性概率重采样与暴雨空间变换相结合的方式进行降雨频率分析，估计本地化的极端暴雨频率。以上海地区为例，研究发现暴雨移置区内暴雨分布具有空间异质性，暴雨随机移置概率不均，计算得到的设计暴雨方案包含了降雨时空分布信息，在不同重现期下设计暴雨的时空结构存在变异性，说明传统方法中采用的简化雨型和均一化空间分布假设会增加设计暴雨的不确定性。     

降雨数据时空精度对城市暴雨变异性及频率分析的影响

提升城市暴雨内涝防治精细化水平是解决城市洪涝问题的关键。采用16种不同时空分辨率的降雨产品,利用暴雨时空异质性评估指标和随机暴雨移置法,在上海地区定量评估降雨数据精度对暴雨事件时空变异性诊断和频率分析的影响。研究发现利用低精度降雨数据得到的年最大暴雨序列发生时间延迟、降水量低估,暴雨过程不均匀性提升、空间不均匀性降低;在不同重现期下,降雨数据精度对频率分析结果影响有显著差异,重现期越大,低精度数据带来的低估程度越大;时间精度的影响占主导地位,可达空间精度的5倍。在城市暴雨洪涝研究中有必要采用更高精度的降雨数据,建议与研究区域类似的小型城市地区在防洪设计中使用精度达(12 h、0.05°)或以上的降雨数据。     

城市暴雨强度公式研究进展与述评

能够客观反映城市降雨特征与规律的暴雨强度公式是城市排水防涝基础设施建设、海绵城市建设过程中相关工程规划、设计的重要前提。简述了暴雨强度公式推求的过程,从暴雨强度公式型式、暴雨资料选样方法、频率曲线选择、频率曲线参数估计以及暴雨强度公式的参数求解等方面,系统梳理了国内外发展现状,深入分析、归纳了各种方法的优缺点,对暴雨强度公式编制过程中存在的两步最优与直接拟合、公式拟合的"异参同效"、公式及参数合理性分析以及编制长历时暴雨强度公式等问题进行深入剖析,认为暴雨强度公式还需在全要素误差分析、成果合理性检验、降雨空间分布、气候变化对城市未来降雨的影响等方面进行深入研究。     

城市设计暴雨频率计算问题

城市设计暴雨,具有历时短、设计标准较低的特点,与常用的频率计算方法不尽相同。简述了暴雨系列的取样问题;改正了与经验频率有关的计算公式;提出以经验适线法来拟合暴雨系列呈反Ｓ形的分布;比较了推求设计暴雨的几种方法,认为超定量综合法有偏于安全的结果;列述了我国一些城市的暴雨强度公式,其中的参数无一定的规律性,期望进一步工作,在点面上进行协调。     

无资料小流域不同暴雨频率计算方法的比较

实践中存在规划小流域降雨资料不足或无降雨资料的情况下,使用三种不同暴雨频率计算方法,即传统矩法、地区综合法和L-矩法来计算不同重现期下小流域的设计暴雨与暴雨过程线.结果表明,L-矩法和地区综合法各有优势,可适用于不同资料情况设计暴雨的计算.分析结果希望为无资料小流域利用暴雨资料推求洪水过程提供一定的借鉴和启示.     

考虑降雨时空变化的单位线研究

流域降雨的时空变异性和地形地貌特征，以及不确定性因素对单位线的影响始终是流域汇流计算方法研究的难点问题。本文分析了传统的根据降雨时空分布不均匀性对单位线进行分类的方法及其缺点，推导了考虑暴雨重心位置和降雨强度的影响的S曲线法，给出了新的S曲线方程，建立了S曲线参数与暴雨重心位置和降雨强度的关系，采用该方法可求得任一暴雨重心位置及任一降雨强度下的时段单位线。该方法具有谢尔曼经验单位线简便实用的特点，又具有考虑降雨时空变异性的优点，在沮河流域洪水预报模型中的应用表明该方法是可行的。     

地区线性矩法在太湖流域暴雨频率分析中的应用

介绍了基于水文气象途径的地区线性矩法的概念,通过基于次序统计量的线性矩进行参数估计与基于水文气象一致区的地区分析法相结合,以太湖流域1d时段的年极值降雨资料为例,进行暴雨频率分析。应用水文气象一致区的判别准则,将太湖流域划分为8个水文气象一致区;综合考虑三种拟合优度检测方法,选择1~8区的最优分布线型分别为:GEV、GLO、GEV、GEV、GNO、GNO、GEV、GNO;根据地区分析法原理,估算各雨量站的暴雨频率设计值。分析表明:太湖流域各重现期下的年极值降雨空间分布形态基本一致,西南山区是太湖流域的暴雨高风险区,应该在地区防洪规划中引起重视。结果表明:地区线性矩法具有很高的学术和实用价值,建议在全国范围内推广,作为防洪规划的顶层设计和基础工作,以满足工程防洪设计、地区防洪规划、山洪预警和城市防涝防洪规划等方面的需求。     

关于设计暴雨推求设计洪水方法的探讨

笔者进行过多次由设计暴雨推求设计洪水的工作，对这一设计洪水计算方法在实际中存在的问题及改进意见进行过探讨，认为现阶段采用的方法在亢进怀设计洪水频率转换，设计暴雨的点在拆算，设计暴雨的特大值处理，产汇流方案的外延使用等方面存在着无法克服的困难。     

我国三峡库区近49年暴雨气候特征分析

根据三峡库区及其周围35个气象站1961～2009年的逐日降雨资料,采用常规统计方法、小波变换等方法,分析了49年来三峡库区暴雨日数的气候变化特征;使用偏态系数与峰度系数方法,对暴雨日数分布的正态性进行了分析。结果表明:49年来,三峡库区的暴雨事件具有显著的年代际变化和区域差异,年平均暴雨日数及其均方差空间分布型态比较一致。历年暴雨日数的偏态系数以正偏为主,峰度系数则以负值为主。     

太湖流域设计暴雨修订

太湖流域属平原河网地区,河网密布、水流流向往复不定,不存在流域出口控制断面,太湖流域设计洪水一般根据设计暴雨采用流域产汇流模型间接推求。因此,设计暴雨成果将直接影响流域防洪规划、工程设计、风险图编制等多项工作,其可靠性关系到流域的防洪安全,是一项十分重要的基础工作。开展了太湖流域设计暴雨修订计算,与太湖流域防洪规划设计暴雨成果对比分析,并针对设计暴雨过程推求采用的不同空间分配方法,进行成果的合理性评估。     

Development of design storm hyetographs in hyper-arid and arid regions: case study of Sultanate of Oman

The temporal distribution of the design storm is an important input in hydrological models. This research aims to develop design storm profiles representative of arid and hyper-arid areas based on actual storm recordings. Two hundred thirty-six rainfall storms were collected from seventeen rainfall gauges that cover the coastal zone of Oman for the period from 1993 to 2007. Storms were classified into four categories according to their total durations. Design storm hyetographs were derived from raw rainfall records for all four categories using the Alternating Block Method (ABM) and were also computed by ABM applied on the Intensity-Duration-Frequency (IDF) curves. Both design storm profiles were compared and it was found that the ABM_IDF storm profiles were equivalent to the four ABM_Storms profiles from a practical point of view as they produce similar peak discharges. The storm profiles developed in the current research were also compared to the commonly used Soil Conservation Service (SCS) dimensionless distributions and the UK50 storm profiles. The results showed that the most conservative commonly used SCS type II and the UK50 summer profiles are not safe to be used in design purposes in arid and hyper arid regions, despite their wide utilization in many codes of practice in these regions. The study recommends using the newly developed dimensionless storm profiles derived from the actual records.     

Development of storm hyetographs for flood forecasting in the Kingdom of Saudi Arabia

This paper presents the derivation of the design storm hyetograph patterns for the Kingdom of Saudi Arabia based on real rainfall events from meteorological stations distributed throughout the Kingdom. Two thousand twenty-seven rainfall storms for a 20–28-year period were collected and analyzed covering 13 regions of the Kingdom. Four distinct dimensionless rainfall hyetograph patterns have been obtained over the Kingdom, while two patterns have been obtained for each individual region because of the lack of data for long-duration storms in individual regions. The resulting dimensionless rainfall patterns for each region can be used to develop storm hyetographs for any design duration, total rainfall depth and return period. It has been shown that the developed storm hyetographs have different features from other storm patterns that are commonly used in arid zones. The study recommends using these curves for the design of hydraulic structures in Kingdom of Saudi Arabia and regions alike.     

Multi-criteria decision-making analysis in selecting suitable plotting positions for IDF curves of storm events

Selecting suitable distributions for rainfall data is usually subjective and complex since it requires decision-makers to consider results from various measures of goodness-of-fit indices. In this study, the VIKOR method in multi-criteria decision-making analysis is modified to select the most suitable plotting positions to represent extreme storm intensities in order to build the intensity–duration–frequency (IDF) curves of storm events. This is done by considering the rankings provided by all goodness-of-fit indices used to obtain a compromise solution. Nine plotting positions are considered: Weibull (W), Adamowski (A), Gringorten (G), Hazen (H) and Gumbel (EV I) and two known plotting positions for generalized extreme value (GEV) distribution using Pearson’s skewness and another two using L-skewness. The IDF curves obtained are compared to a reference IDF curves which was found using the GEV distribution. The mean and median for three goodness-of-fit indices, the coefficient of variation of root mean square error, CV_RMSE, the mean percentage of difference, Δ, and the coefficient of determination, R ², are taken as the criteria for selection process. The results show that six plotting positions, A, H, W, G and the two plotting positions with L-skewness, are equally superior compared to the other three plotting positions.     

Modelling a storm surge under future climate scenarios: case study of extratropical cyclone Gudrun (2005)

Weather Research and Forecasting atmosphere model and Finite Volume Community Ocean Model were for the first time used under the pseudo-climate simulation approach, to study the parameters of an extreme storm in the Baltic Sea area. We reconstructed the met-ocean conditions during the historical storm Gudrun (which caused a record-high +275 cm surge in Pärnu Bay on 9 January 2005) and simulated the future equivalent of Gudrun by modifying the background conditions using monthly mean value differences in sea surface temperature (SST), atmospheric air temperature and relative humidity from MIROC5 in accordance with the IPCC scenarios RCP4.5 and RCP8.5 for 2050 and 2100. The simulated storm route and storm surge parameters were in good accordance with the observed ones. Despite expecting the continuation of recently observed intensification of cyclonic activity in winter months, our numerical simulations showed that intensity of the strongest storms and storm surges in the Baltic Sea might not increase by the end of twenty-first century. Unlike tropical cyclones, which derive their energy from the increasing SST, the extratropical cyclones (ETCs) harvest their primary energy from the thermal differences on the sides of the polar front, which may decrease if the Arctic warms up. For climatological generalizations on future ETCs, however, it is necessary to re-calculate a larger number of storms, including those with different tracks and in different thermal conditions.     

Preparedness and storm hazards in a global warming world: lessons from Southeast Asia

The 2007 Intergovernmental Panel on Climate Change (IPCC) Assessment Report 4 found an average increase in global surface temperature of 0.74°C between 1906 and 2005. There is general agreement in the literature that the frequency of extreme precipitation events in Southeast Asia will increase with global warming. In particular, the potential impact of associated storm hazards will render the densely populated countries in Southeast Asia vulnerable to such changes in precipitation events. One main adaptation strategy given such impending changes is preparedness. Using existing literature and historical meteorological data, this paper establishes that Southeast Asia is indeed experiencing storms of higher intensities and more frequently. Two case of extreme storm event in Southeast Asia, the extreme high rainfall event in December 2006 in Southern Johor and Typhoon Vamei, are presented to consider the implications of the increased storm activities due to global warming. These two examples also discuss the need for preparedness in adapting to the impact of global warming.     

Modeling the impact of land reclamation on storm surges in Bohai Sea,China

A nested model for the simulation of tides and storm surges in the Bohai Sea, China, has been developed based on the three-dimensional finite-volume coastal ocean model. The larger domain covers the entire Yellow Sea and Bohai Sea with a horizontal resolution of ~10 km, and the smaller domain focuses on the Bohai Sea with a fine resolution up to ~300 m. For the four representative storm surges caused by extratropical storms and typhoons, the simulated surge heights are in good agreement with observations at coastal tide gauges. A series of sensitivity experiments are carried out to assess the influence of coastline change due to land reclamation in recent decades on water levels during storm surges. Simulation results suggest that changes in coastline cause changes in the amplitude and phase of the tidal elevation, and fluctuations of surge height after the peak stage of the storm surges. Hence, for the assessment of the influence of coastline changes on the total water level during storm surges, the amplitudes and phases of both the tidal and surge heights need to be taken into account. For the three major ports in the Bohai Bay, model results suggest that land reclamation has created a coastline structure that favors increasing the maximum water level by 0.1–0.2 m. Considering that during the storm surges the total water level is close to or even exceeds the warning level for these ports, further increasing the maximum water level by 0.1–0.2 m has the potential to cause severe damages and losses in these ports.

     

Advances in surrogate modeling for storm surge prediction: storm selection and addressing characteristics related to climate change

This paper establishes various advancements for the application of surrogate modeling techniques for storm surge prediction utilizing an existing database of high-fidelity, synthetic storms (tropical cyclones). Kriging, also known as Gaussian process regression, is specifically chosen as the surrogate model in this study. Emphasis is first placed on the storm selection for developing the database of synthetic storms. An adaptive, sequential selection is examined here that iteratively identifies the storm (or multiple storms) that is expected to provide the greatest enhancement of the prediction accuracy when that storm is added into the already available database. Appropriate error statistics are discussed for assessing convergence of this iterative selection, and its performance is compared to the joint probability method with optimal sampling, utilizing the required number of synthetic storms to achieve the same level of accuracy as comparison metric. The impact on risk estimation is also examined. The discussion then moves to adjustments of the surrogate modeling framework to support two implementation issues that might become more relevant due to climate change considerations: future storm intensification and sea level rise (SLR). For storm intensification, the use of the surrogate model for prediction extrapolation is examined. Tuning of the surrogate model characteristics using cross-validation techniques and modification of the tuning to prioritize storms with specific characteristics are proposed, whereas an augmentation of the database with new/additional storms is also considered. With respect to SLR, the recently developed database for the US Army Corps of Engineers’ North Atlantic Comprehensive Coastal Study is exploited to demonstrate how surrogate modeling can support predictions that include SLR considerations.     

Sensitivity analysis of runoff hydrographs due to temporal rainfall patterns in Makkah Al-Mukkramah region,Saudi Arabia

Runoff peak and volume in flood studies are estimated relying on temporal rainfall distribution from various storm patterns. Usually, SCS distributions types (I, II, III, IA) are commonly used. Using these distributions in runoff calculations assume that the in situ temporal rainfall pattern typically behaves as the one described by the SCS-type distribution, which is due to cyclonic frontal storms and actually developed in temperate environment. To what extent such assumption is valid in the arid environment? How much the impacts of rainfall temporal patterns are reflected in runoff volumes and peaks? The aim objectives of the current study are to answer the above two questions and clarify the validity of aforementioned assumption and exemplify such effect. Real rainfall data collected from rain gauges of Makkah Al-Mukkramah region over a period of more than 20 years are utilized. Temporal rainfall patterns and their parameters are deduced. Many hydrological simulations are performed and comparisons, in terms of runoff volume and peak flows, are made to show the effects of the common rainfall storm patterns and the developed rainfall storm patterns in the region based on the current study. Results indicate that major bursts of the design rainfall storm pattern are located in the first time of the storm period in the two quartiles which is mainly due to convective rainfall type in thunderstorms unlike the commonly used by SCS types relying on frontal cyclonic storms. Makkah Al-Mukkramah temporal rainfall pattern does not behave as the “typical pattern” assumed by SCS distributions that are deduced from different environments. The impacts of the temporal pattern reflected as an overestimate in the runoff peak reached to 68 %. The developed hyetographs and tables presented in the current study are recommended to enhance economical and rational design practice in watersheds of Makkah Al-Mukkramah region.