Projected Changes in Temperature and Precipitation Extremes over China as Measured by 50-yr Return Values and Periods Based on a CMIP5 Ensemble

Future changes in the 50-yr return level for temperature and precipitation extremes over China's Mainland are investigated based on a CMIP5 multi-model ensemble for RCP2.6, RCP4.5 and RCP8.5 scenarios. The following indices are analyzed： TXx and TNn （the annual maximum and minimum of daily annual maximum consecutive 5-day precipitation） and CDD maximum and minimum surface temperature）, RX5day （the （maximum annual number of consecutive dry days）. After first validating the model performance, future changes in the 50-yr return values and return periods for these indices are investigated along with the inter-model spread. Multi-model median changes show an increase in the 50-yr return values of TXx and a decrease for TNn, more specifically, by the end of the 21st century under RCP8.5, the present day 50-yr return period of warm events is reduced to 1.2 yr, while extreme cold events over the country are projected to essentially disappear. A general increase in RX5day 50-yr return values is found in the future. By the end of the 21st century under RCP8.5, events of the present RX5day 50-yr return period are projected to reduce to 〈 10 yr over most of China. Changes in CDD-50 show a dipole pattern over China, with a decrease in the values and longer return periods in the north, and vice versa in the south. Our study also highlights the need for further improvements in the representation of extreme events in climate models to assess the future risks and engineering design related to large-scale infrastructure in China.

A new method to estimate wave height of specified return period

In this paper, we propose a new method to estimate the wave height of a specifi c return period based on the Hurst rule and a self-affi ne fractal formula. A detailed description of our proposed model is presented in this paper. We use the proposed model to analyze wave height data recorded along the coast of Chaolian Island from 1963 to 1989. The results show that the performance of our proposed model in estimating design wave heights is superior to traditional models.

Typhoon wind hazard model and estimation on return period of typhoon wind speed

Typhoons are one of the most serious natural disasters that occur annually on China’s southeast coast.A technique for analyzing the typhoon wind hazard was developed based on the empirical track model,and used to generate 1000-year virtual typhoons for Northwest Pacific basin.The influences of typhoon decay model,track model,and the extreme value distribution on the predicted extreme wind speed were investigated.We found that different typhoon decay models have least influence on the predicted extreme wind speed.Over most of the southeast coast of China,the predicted wind speed by the non-simplified empirical track model is larger than that from the simplified tracking model.The extreme wind speed predicted by different extreme value distribution is quite different.Four super typhoons Meranti(2016),Hato(2017),Mangkhut(2018)and Lekima(2019)were selected and the return periods of typhoon wind speeds along the China southeast coast were estimated in order to assess the typhoon wind hazard.

Hydrology and Estimation of Real Erosion in the Patria Nueva Micro-Basin for Five Return Periods

This paper will discuss the actual erosion estimation of the Patria Nueva micro basin in tons/ha/year (E), located in Tuxtla Gutiérrez Chiapas, Mexico. We used the universal soil loss equation (USLE), considered one of the best theoretical tools for planning and soil preservation in the USA and other countries. The actual erosion rates were estimated for 5, 20, 50, 100, and 500 years return periods (Rp), with elevated results due to high degrees of anthropogenic alteration of the micro-basin, especially in the last 50 years. High erosion rates generate the following problems: loss of soil, which is unfavorable for plant life, due to the soil being a non-renewable resource, the undermine can never renovate, the hydraulic area in the main channel reduces during the rainy season (when the river overflows). The sediment accumulates at the lower part of the micro-basin along with waste, garbage, and mud.

Climate Change Characteristics and Return Periods of Heavy Precipitation in the Northeast Side of Qinghai-Tibet Plateau

[ Objective] The study aimed to discuss analyze climate change characteristics and return periods of heavy precipitation in the northeast side of Qinghai-Tibet Plateau. [ Method] Based on the data of daily precipitation from 1943 to 2008 in 6 representative meteorological stations in Linxia located in the northeast side of Qinghai-Tibet Plateau, the climate change characteristics of heavy precipitation were analyzed, and the return periods of heavy precipitation were calculated by Pearson-Ill probability distribution method. [ Result] Days of heavy precipitation in Linxia region in- creased conspicuously since the 1990s. The return periods of heavy precipitation in the six stations on August 20, 2008 were consistent with the re- sults of artificial estimation. [ Conclusion] The research could provide scientific references for the reasonable utilization of climate resources, disas- ter prevention and rational arranqement of anricultural plantina svstems in Linxia reaion.

Risk Assessment and Simulation on Storm Flood of the 100-Year Return Period in Hunhe River Basin

Based on the meteorological and geographic information data, with statistical method and the FloodArea model, the extreme daily rainfall of the 100-year return period in Hunhe River basin was established, through the simulation of rainstorm and flood disaster, characteristics of flood depth in warning spot Cangshi village in the upstream of the river were analysed, and possible effect on community economy was also evaluated. Results showed that, the precipitation of 100-year return period occurred, the flood depth has been below 1.0 meter in the most areas of Hunhe River basin, the depth was between 1.0 meter and 2.5 meters in the part areas of Hunhe River basin, and the flood depth has been exceed 2.5 meters in a small part of Hunhe River basin. After the beginning of precipitation, the flood was concentrated in the upper reaches of the river. With the accumulation of precipitation and the passage of time, the flood pools into midstream and downstream. Precipitation lasted for 24 hours, the warning spot was flooded in the beginning of precipitation. With the accumulation of precipitation, water level of the river increases gradually. The depth of warning spot has passed 1.0 meter at the 07 time of the whole process, and the maximum value of flood depth at warning spot was 1.083 meters that occurred at the 19 time. The flood depth of warning spot decreased gradually after the precipitation stopping, and the depth has been below 0.2 meters, the flood of upstream ended. Up to the end of the upstream flood process, in the whole river, about one million five hundred and sixty thousand people were affected by flooding, and thirty-eight billion and two hundred million RMB of gross domestic product were lost, in addition, dry land and paddy field were affected greatly, but woodland and grassland were less affected.

Spatial Distribution of Return Period in China Based on b-value Obtained by Using a New Method

The seismicity in the territory of China, a seismotectonically complicated region, has been examined by using some complete samples of the earthquakes occurred during the last two centuries (1800 - 1999). The A-value of the Gutenberg-Richter relation was estimated by using those data samples. Taking into account the fact that the b-value is spatially more stable than the a value, the b values were calculated at the nodes of a normal grid superposing on the whole area studied and their distribution were examined. The results show that the b values increase smoothly from 0.4 to 0.93. Furthermore, keeping the b values obtained fixed, the a value distribution was also examined. In order to display more detailed information about the seismicity, smaller cell surface (10000 km2) for the calculation of the a value has chosen. The mean return period for different magnitudes was also calculated for each small cell.

Joint Occurrence Period of Wind Speed and Wave Height Based on Both Service Term and Risk Probability

Return periods calculated for different environmental conditions are key parameters for ocean platform design.Many codes for offshore structure design give no consideration about the correlativity among multi-loads and over-estimate design values.This frequently leads to not only higher investment but also distortion of structural reliability analysis.The definition of design return period in existing codes and industry criteria in China are summarized.Then joint return periods of different ocean environmental parameters are determined from the view of service term and danger risk.Based on a bivariate equivalent maximum entropy distribution,joint design parameters are estimated for the concomitant wave height and wind speed at a site in the Bohai Sea.The calculated results show that even if the return period of each environmental factor,such as wave height or wind speed,is small,their combinations can lead to larger joint return periods.Proper design criteria for joint return period associated with concomitant environmental conditions will reduce structural size and lead to lower investment of ocean platforms for the exploitation of marginal oil field.

泥石流危险范围Laharz修正模型及其应用

泥石流危险区研究涉及触发条件、物源与地形等多种因素,需要开发快速、有效的方法进行危险范围分析。本文基于Laharz基本原理,以泥石流样本为数据基础拟合得到修正模型,并以重庆市巫溪县杨家湾沟为例,采用修正的Laharz ArcGIS工具包,在不同降雨重现期条件下对泥石流堆积范围进行模拟计算。结果表明:1)采用修正参数使Laharz模型统计量参数的和方差(SSE)和均方根误差(RMSE)减小,确定系数(R^(2))增大,拟合优度得到明显提高;2)基于数字高程模型,结合现场调查推算的物源体积,在ArcGIS平台采用Laharz工具包可快速模拟不同降雨重现期(10、20、50、100 a)条件下的泥石流堆积范围,并且模拟泥石流堆积宽度与现场调查堆积范围接近,大部分重合;3)采用Laharz修正模型与传统的FLO-2D软件模拟进行对比,其中最远冲出距离、最大堆积宽度和堆积面积在两种方法下模拟结果的差值比率分别在10.00%、15.00%和20.00%量级,采用两种方法模拟结果与实地勘查结果也相近,表明Laharz修正模型具可靠性。

下沉式地铁车辆基地防洪排涝设计标准研究

[目的]下沉式地铁车辆基地是一种特殊空间利用形式的车辆基地,在防洪排涝方面存在较大风险,但国内现有相关规范和标准中尚无针对这方面的规定。因此,需对下沉式车辆基地防洪排涝设计能力进行深入研究,明确规范和标准中的相关内容,为此类项目建设提供设计依据。[方法]以宁波地铁5号线前殷停车场工程为例,分析了现有规范和标准中有关防洪和排水的设计要求,分析了下沉车辆基地的防洪涝设计方案,分别按50年和100年暴雨重现期对下沉基坑内不同区域防洪涝设计方案进行了对比分析。[结果及结论]下沉式车辆基地应采用“可靠的防、排内涝水措施”来满足防洪排涝的基本要求。在防洪涝方面,下沉式车辆基地防洪墙顶高程和出入口路面高程应高于百年洪水位+安全高,同时防洪墙与周边地面的高差应高于100年暴雨重现期下的所在地块内涝水位。在排涝方面,下沉基坑内的盖体屋面区域排水宜遵循“高水高排”的原则,按100年暴雨重现期设计屋面排水能力,通过重力流方式直排至基坑外;坑内敞开区域采用抽排方式,按100年暴雨重现期设计雨水泵站的总排水能力。

高寒气候区生长季NDVI与昼夜不对称增温的Copula分析

利用1982—2016年的青海地区归一化植被指数和气象数据,基于马尔科夫链蒙特卡罗的Copula函数方法,深入探索昼夜增温不对称性与植被活动之间的复杂关系,揭示了昼夜增温和NDVI之间的联合概率分布及其季节性差异。研究结果表明,昼夜增温与NDVI之间的关系在不同季节呈现显著差异。尤其在秋季,昼夜增温对NDVI的影响最为显著,其次是夏季和春季。通过Copula函数模型,发现昼夜增温与NDVI在特定温度区间内呈现正相关,表明适宜的温度条件下昼夜增温对植被生长具有促进作用。然而,当昼夜增温超过某一阈值时,其对NDVI的促进作用转变为抑制作用,从而限制了植被的生长。同时,还揭示了重现期与昼夜增温及NDVI之间的关系。在较低的重现期下,昼夜增温与NDVI的联合概率较高,表明在这些条件下,植被生长良好的情况出现的频率较高。反之,较高的重现期对应于昼夜增温与NDVI较低的联合概率,表明植被生长受到抑制。本研究通过Copula函数提供了一个全新的视角来理解昼夜增温与植被动态之间的相互作用,强调了气温变化对植被生长影响的复杂性。

大桥桥位不同重现期年最大风速推算

大风是威胁桥梁安全的主要灾害之一,是大型桥梁工程设计的关键,它影响到整个工程的安全性。科学的桥梁抗风设计可以有效预防或降低风险,减少损失。以安徽马鞍山长江大桥为例,借助当涂气象站1960—2022年逐年风速资料,采用时距一致性订正方法,建立相应时段当涂县气象站10 m高度10 min平均年最大风速系列(其中2000—2008年逐年最大风速,通过与未受城市化影响的马鞍山气象站比较进行了合理订正),利用耿贝尔法推算出大桥桥位区不同高度不同重现期10 min平均年最大风速。结果表明:马鞍山长江大桥桥位区不同重现期(100 a,50 a,30 a)10 m高度10 min平均年最大风速分别为28.8 m/s、27.2 m/s和26.0 m/s。利用指数和对数法,将桥位区风速外推到200 m以下每10 m高度层最大风速。

基于不确定性的多尺度暴雨强度和外江洪水位联合分布研究

城市洪涝治理方案以及排涝设施规模建设都与城市暴雨强度和外江洪水位息息相关,因此需要对暴雨强度与外江洪水位联合概率分布进行深入研究。以武汉市为例,采用Copula函数建立小时尺度城市暴雨强度和外江洪水位的联合分布,使用极大似然估计值(Max-Likelihood)、模型选择准则、RMSE和NSE拟合优度来评估不同Copula模型的性能,利用局部优化(Local optimization,LO)和马尔科夫链蒙特卡洛(Markov chain Monte Carlo,MCMC)方法来分析Copula模型的不确定性。结果表明:暴雨强度和外江洪水位两要素存在明显的正相关,1 h最大连续降水量和最大日水位相关性最高,最优联合分布函数为Gumbel Copula函数;模型不确定性分析表明MCMC模拟的最优参数与理论参数值基本吻合,效果明显优于局部优化算法,且模型不确定性结果与拟合优度评价结果一致,进一步验证了联合分布函数参数的有效性。相同频率情况下,单变量值低于两变量联合频率对应的暴雨强度和外江洪水位值,高于两变量同现频率对应的暴雨强度和外江洪水位值;两变量同现重现期高于单变量设计重现期,而联合重现期低于单变量设计重现期。同频率下的暴雨强度与水位的组合风险率都远远低于单变量情况下的频率值,50 a以上排涝风险率大于设计暴雨重现期,但最大不超过联合风险率。

渤海和黄海北部工程设计冰厚变化趋势分析

针对渤海和黄海北部沿岸风电、光伏和核电等新兴能源中的工程海冰设计问题,本文研究了重现期冰厚及其在大气候背景下的变化趋势。本文分析72 a冰级时间序列表明渤海和黄海北部总体冰情等级呈明显下降趋势;在此影响下,基于20 a渤海和黄海北部海冰多源观测数据和精细化海冰数值预报资料,研究发现不同重现期冰厚较之前海冰区划值存在不同程度的降低。此外,不同场址设计冰厚受当地海洋环境条件影响较大,单一参考海冰区划值可能存在较大误差。研究表明:针对特定作业地点的工程设计冰厚,需要有针对性地开展精细化评估并考虑大气候背景变化的影响,才能为相关工程海冰参数设计提供更加可靠的依据。

基于地区线性矩法的四川省24 h极值降雨频率分析

为探究四川省24 h极值降雨在不同重现期不同频率下的时空分布特征,采用地区线性矩法划分四川省水文气象一致区,确定最优拟合线型,并验证地区线性矩法在站点稀疏地区的适用性,随后估计四川省24 h不同重现期降雨频率值,分析其时空分布特征。研究结果表明:(1)四川省可划分为40个水文气象一致区,经线型拟合优度检验,主要线型为GLO、GEV和GNO,其中川西高原地区的最优线型大多为GLO,盆地区域的最优线型大多为GEV。(2)地区线性矩法在站点相对稀疏的川西高原地区具有良好的适用性。(3)四川省内不同地区24 h极值降雨空间分布十分不均,同一重现期下不同地区降雨频率估计值的最大值可达最小值的10倍。

降雨雨型对城市雨水系统内涝弹性的影响

为探究降雨雨型对城市雨水系统内涝弹性的影响,基于MIKE FLOOD平台,以济南市新旧动能转换起步区大桥分区为研究对象,对7种重现期、3种降雨历时和3种雨峰系数的设计降雨雨型进行内涝过程场景推演,并结合层次分析法,以积水量、积水面积和平均积水深度为基础量化系统内涝弹性。结果表明:积水量峰值、积水面积峰值均随重现期、降雨历时的增大而增大,平均积水深度波动较大;系统性能前后主要发生两次波动,分别由降雨强度变化和研究区大部分洼地深度较浅导致;随着重现期的增加,系统内涝弹性越小,单位雨峰系数引起的系统内涝弹性极值对应的降雨量差异越来越大,整体上,降雨雨峰越居中和降雨历时越大,系统内涝弹性越小。

柬埔寨磅逊湾口波高推算与分析

深水波高的推算是工程建设选址的重要影响因素,柬埔寨磅逊湾波浪具有明显的季风期特征,并且在一定程度上受到台风浪影响。作为“一带一路”中海上丝路的重要枢纽,其已有的研究成果较少。文章利用连续30 a的美国关岛联合台风警报中心(JTWC)台风数据以及欧洲中期天气预报中心(ECMWF)再分析数据,在实测数据验证基础上,计算得到台风浪波高,再结合ECMWF再分析数据,得到了1990—2019年湾口主要波浪入射方向的波高年极值,最后利用P-Ⅲ曲线计算得到不同重现期波要素。研究成果可为后续磅逊湾内港口、电厂以及岛桥建设提供波浪条件,对其湾内的工程规划、立项、实施有借鉴意义。

长江口徐六泾水文站极值水位研究

在气候变化背景下,极端天气和水位事件频发。为了分析长江口极端潮位的长周期特征,研究基于极值理论相关方法,采用近33 a实测资料对长江口极值潮位趋势性和重现期进行分析,结果表明:长江口徐六泾站年极值水位呈轻微下降趋势,直接原因是大通流量减少导致当地年均海面的下降;区分组模型结果显示,台风“温妮”期间长江口造成的风暴潮位为100 a一遇,而POT模型计算结果仅为60 a一遇,100 a一遇重现期潮位约7.0 m;潮位重现期的计算本质是一种用频率代替概率、从样本推求整体的过程,具有一定不确定性。其意义在于以可获取的数据为基础,计算事件发生的风险率,旨在为工程设计或风险管理提供依据。

夏闲期玉米压青对旱地麦田土壤水分周年变化的影响

[目的]揭示旱地麦田土壤水分对夏闲期玉米压青的周年适应变化规律,阐明压青模式对小麦产量提高及优化的水分驱动机制,为旱作压青蓄水技术提供理论参考。[方法]通过晋南旱地麦田夏闲期玉米压青还田试验,采用大区对比方法,以夏闲期免耕处理为对照,研究夏闲期玉米压青模式下麦田土壤周年贮水耗水变化规律,分析了其对后茬小麦产量的影响及水分利用效率。[结果]与免耕模式相比,夏闲期玉米压青处理可显著提高0—200 cm土壤周年贮水量,且对100—200 cm较深层土壤的蓄水能力更强;玉米压青处理0—200 cm土壤周年耗水量及耗水百分比均显著低于免耕处理;与免耕相比,压青处理可提高夏闲期0—200 cm土层盈水量,减少小麦季0—100 cm浅土层的水分耗散量;压青处理小麦穗数、穗粒数显著高于免耕,而千粒重差异较小;压青处理夏闲期0—200 cm土壤对降雨的蓄水效率显著高于免耕;在夏闲期玉米压青还田生物量显著高于免耕处理条件下,小麦季和周年阶段,压青处理生物产量及籽粒产量的降水、水分利用效率均显著高于免耕处理。[结论]在旱地麦田丰水年份,夏闲期玉米压青可显著提高旱地麦田土壤贮水,降低作物周年耗水量,优化小麦产量三要素,蓄水增产。

重庆区域性暴雨过程的重现期评估模型构建方法研究

提出一种利用重现期方法构建区域性暴雨过程的评估模型,用于全面评估暴雨过程发生的频率和强度。基于2011—2021年重庆市114次区域性暴雨过程的小时雨量数据及暴雨灾情数据,利用概率分布函数拟合、重现期计算、相关分析等方法,构建区域性暴雨过程的重现期评估模型,并开展业务检验。结果表明:(1)利用自建的重现期计算公式,得到暴雨过程特征量的重现值与原始值的误差小于10%,重现期计算结果准确性较高。(2)构建的重现期评估模型与直接经济损失的正相关系数可通过0.001显著性水平检验,较现行业务指标提高16%。(3)历史回算和独立样本检验结果显示,重现期评估模型与业务指标评估等级一致率达70%,模型稳定性强且能反映事件发生频率和强度,可为区域性暴雨过程评估提供新思路。