小流域山洪灾害危险性分析之降雨指标选取的初步研究

降雨是诱发山洪灾害的直接动力和激发条件,是山洪灾害危险性分析中不可或缺的重要指标。对于不同的研究区,不同频次和历时的降雨对山洪灾害的影响不同,危险性分析所选取的降雨指标也可能不同。本文基于1:5万小流域数据、历史山洪灾害空间分布数据和暴雨图集资料,以江西省婺源县小流域为例,采用相关分析法对初步选取的24个降雨指标进行相关性分析,筛选出相关性不强的降雨指标;利用GIS技术和基于局部Getis-Ord Gi*算法的优化热点分析工具对历史山洪灾害点进行空间聚类分析,获得研究区每个小流域山洪灾害危险度的估值,该值能够较好地反映小流域山洪灾害危险性的空间分布;通过地理探测器模型中的因子探测器和交互探测器对已筛选出的降雨指标和小流域山洪灾害危险度进行综合探测分析,从而获取对该研究区小流域山洪灾害危险性影响较大的降雨指标,即100年一遇最大6 h降雨和100年一遇最大24 h降雨。本文研究对小流域山洪灾害危险性分析降雨指标的定量选取具有参考和指导意义。     

Metocean design parameter estimation for fixed platform based on copula functions

Considering the dependent relationship among wave height, wind speed, and current velocity, we construct novel trivariate joint probability distributions via Archimedean copula functions. Total 30-year data of wave height, wind speed, and current velocity in the Bohai Sea are hindcast and sampled for case study. Four kinds of distributions, namely, Gumbel distribution, lognormal distribution, Weibull distribution, and Pearson Type III distribution, are candidate models for marginal distributions of wave height, wind speed, and current velocity. The Pearson Type III distribution is selected as the optimal model. Bivariate and trivariate probability distributions of these environmental conditions are established based on four bivariate and trivariate Archimedean copulas, namely, Clayton, Frank, Gumbel-Hougaard, and Ali-Mikhail-Haq copulas. These joint probability models can maximize marginal information and the dependence among the three variables. The design return values of these three variables can be obtained by three methods: univariate probability, conditional probability, and joint probability. The joint return periods of different load combinations are estimated by the proposed models. Platform responses (including base shear, overturning moment, and deck displacement) are further calculated. For the same return period, the design values of wave height, wind speed, and current velocity obtained by the conditional and joint probability models are much smaller than those by univariate probability. Considering the dependence among variables, the multivariate probability distributions provide close design parameters to actual sea state for ocean platform design.     

强降水的GP分布拟合

根据极值理论中处于重要地位的GP分布模型，讨论了模型中的形状参数、位置参数及尺度参数的算法，并将其用于拟合呈偏斜状态的月和日降水量资料中强降水部分，得到强降水发生的直观年数。     

Determination of water level design for an estuarine city

Based on the extreme value theory,self-affinity,and scale invariance,we studied the temporal and spatial relationship and the variation of water level and established a model of Gumbel-Pareto distribution for designed flood calculation.The model includes the previous extreme value models,the over-threshold data,and the fractal features shared by previous extreme value models.The model was simplified into a logarithmic normal distribution and a Pareto distribution for specific parameter values,and was used to calculate the designed flood values for the Shanghai Wusong Station in 100-and 1 000-year return periods.The calculated results show that the value of the designed flood height calculated in the Gumbel-Pareto distribution is between those in the Gumbel and Pearson-III distributions.The designed flood values in the100-and 1 000-year return periods of the model were 0.0 3%and 0.11%lower,respectively,than the Gumbel distribution and 0.06%and 1.54%higher,respectively,than the Pearson-III distribution.Compared to the traditional model based solely on extreme probability,the Gumbel-Pareto distribution model could better describe the probabilistic characteristics of extreme marine elements and better use the data.     

Long-term statistics of extreme tsunami height at Crescent City

Historically, Crescent City is one of the most vulnerable communities impacted by tsunamis along the west coast of the United States, largely attributed to its offshore geography. Trans-ocean tsunamis usually produce large wave runup at Crescent Harbor resulting in catastrophic damages, property loss and human death. How to determine the return values of tsunami height using relatively short-term observation data is of great significance to assess the tsunami hazards and improve engineering design along the coast of Crescent City. In the present study, the extreme tsunami heights observed along the coast of Crescent City from 1938 to 2015 are fitted using six different probabilistic distributions, namely, the Gumbel distribution, the Weibull distribution, the maximum entropy distribution, the lognormal distribution, the generalized extreme value distribution and the generalized Pareto distribution. The maximum likelihood method is applied to estimate the parameters of all above distributions. Both Kolmogorov-Smirnov test and root mean square error method are utilized for goodness-of-fit test and the better fitting distribution is selected. Assuming that the occurrence frequency of tsunami in each year follows the Poisson distribution, the Poisson compound extreme value distribution can be used to fit the annual maximum tsunami amplitude, and then the point and interval estimations of return tsunami heights are calculated for structural design. The results show that the Poisson compound extreme value distribution fits tsunami heights very well and is suitable to determine the return tsunami heights for coastal disaster prevention.     

1980-2015年黄河流域降雨侵蚀力时空变化分析

本文利用1980-2015年黄河流域及周边166个气象站点36 a的降雨资料,采用日降雨侵蚀力计算模型,对克里金插值后的栅格数据,通过利用主成分分析法、isodata聚类和最大似然法实现区域划分,并在此基础上应用重心模型研究了黄河流域降雨侵蚀力的时空变化。研究结果表明：黄河流域内不同区域的年降雨侵蚀力差异较大,最小的区域在200 MJ·mm·hm^-2·h^-1左右变化,最大的区域可达3000 MJ·mm·hm^-2·h^-1,年降雨侵蚀力具有由西北向东南递增的趋势。年降雨侵蚀力大的区域其侵蚀力值在不同年份中波动范围也大。西宁、呼和浩特等所在的一区、二区和三区的年降雨侵蚀力的重心总体上呈现向东北方迁移趋势。太原、西安所在的四区、五区其重心总体上呈现向西南方迁移趋势,其年降雨侵蚀力重心迁移范围小,重心点分布更紧密。各区域年降雨侵蚀力重心的迁移范围在空间和时间尺度上总体呈现由西北向东南方向逐渐缩小趋势。     

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.     

新疆阿克苏河流域降水空间变异特征分析

根据阿克苏河流域降水空间观测数据,其降水稀疏且分布不均匀的特点,选取不同模型对降水空间变化规律进行研究,其结果精确性差异很大。通常应用地统计理论研究降水空间变异性,一般只涉及单个变量,传统的多元回归分析虽然涉及多个变量的影响,但缺乏区域化的空间结构特征。揭示具有协同区域化特征的降水空间变异现象及建立其空间分布模型,既要考虑多元信息的空间位置关系,即同一变量在不同地理位置上的相关性,又要考虑多元信息由于空间重复性引起的协同关系,即同一地理位置上不同变量的相关性。本文用阿克苏河流域范围内的降水观测数据建立析取-协克立格模型,考虑高程变量对降水量空间分布的影响,定量地揭示降水区域化变量的空间变异规律,并将其结果用于降水量的空间最优插值。     

Effect of the Zagros Mountains on the spatial distribution of precipitation

In order to examine the effect of the Zagros Mountains on precipitation, first, the annual and Seasonal rainfall indices （rain days frequency, rain amount, daily rainfall intensity, and heavy rains） from 43 stations in 1995 - 2004 between the 30° N to 35° N parallels over the mountain range were analyzed. Second, the effect of the Zagros Mountains was studied through the computation of the spatial correlations between the precipitation parameters and the topographic indices （station site elevation, station mean elevation within a radius of 2.5 km, mean elevation of 9 blocks along each of the eight Cartesian directions, and the elevation differences of these 9 blocks from the station mean elevation）. The results showed that in the cold season the maximal rainfall occurs on the upper range of west slope, while in warm season it spreads over the study area. The correlations between precipitation and elevation indices were positive on the north of the stations and negative on the south of the stations, that is, the higher elevations of the stations to the north force the uplifting of the moist air masses and increase rainfall at the stations, while the lower elevations to their south lead the movement of the moist air masses to the stations. This is due to the fact that these stations or slopes are exposed to the moist air masses coming from the Mediterranean Sea and the Persian Gulf. The heavy rain days and the summer sporadic rain events do not show significant correlations with the topographic indices. The findings indicate that the Zagros Mountains intensify the cold period frontal rains especially over the west slope and block the moist air masses from entering the interior parts of the country. Moreover, these mountains play a secondary role in creating rain days. But they are very important in the production of precipitation in the area. Therefore, their absence will decrease the amount of rainfall to their west and, in return, expand the dry climates of their west and east.     

基于TRMM数据的福建省降水时空格局BME插值分析

传统空间插值方法可获得福建省区域内降水的总体分布,但该地区气象站点较稀疏且分布不均,导致该区域内降水的空间插值结果误差较大。为提高插值精度,本文利用TRMM卫星数据以弥补站点数据的不足,尝试将TRMM数据作为"软数据"、台站数据作为"硬数据",两者相结合后采用贝叶斯最大熵(Bayesian Maximum Entropy,BME)方法对福建省降水的时空格局进行分析。以2000-2012年近13年20个气象站点的年降水量和月降水量为基础数据,分别利用普通克里格法(Ordinary Kriging,OK)和TRMM为"软数据"的BME插值法,分析福建省多年降水的时空分布格局,并对2种方法的插值结果进行比较。结果表明:在时空分布上,以TRMM数据为辅助变量的贝叶斯最大熵插值结果能更好地体现降水的局部差异特征;在误差评价上,以TRMM数据为辅助变量的贝叶斯最大熵插值结果的MAE和RMSE较小,表明TRMM数据作为"软数据"参与插值的BME方法可以在一定程度上弥补站点数据的不足,有效降低预测结果的绝对误差。通过对福建省降水插值的时空分布格局分析和误差评价可看出,BME插值法通过对基础台站数据,以及TRMM卫星产品数据的利用,使降水的时空分析结果更加真实客观,同时,为TRMM卫星降水数据的应用提供了一个新思路。     

Characteristics of rainfall erosivity based on tropical rainfall measuring mission data in Tibet, China

Rainfall erosivity in Tibet from 2000 to 2OlO was estimated based on simplified erosion prediction model using daily rainfall data derived from the Tropical Rainfall Measurement Misssion （TRMM） 3B42 rainfall measurement algorithm. Semi- monthly erosive rainfall and rainfall erosivity were validated using weather station data. The spatial distribution of annual rainfall erosivity as well as its seasonal and annual variation in Tibet was also examined. Results showed that TRMM 3B42 data could serve as an alternative data source to estimate rainfall erosivity in the area where only data from sparsely distributed weather stations are available. The spatial distribution of rainfall erosivity in Tibet generally resembles the distribution of multi-year average of annual rainfall. Annual rainfall erosivity in Tibet decreased from the southeast to the northwest. The concentration degree of rainfall erosivity shows an increasing trend from the southeast to the northwest. High rainfall erosivity accompanies low rainfall erosivity concentration degree and vice versa. Rainfall erosivity increased in the middle and western Tibet and decreased in the southeastern Tibet during the 11 years of this study.     

Characteristics of extreme temperature event and its response to regional warming in Northwest China in past 45 years

Using the daily maximum and minimum temperature dataset from 128 stations from 1960 to 2004 in Northwest China, daily extreme high temperature （EHT） and extreme low temperature （ELT） thresholds were determined by centesimal method for different stations at first, then yearly EHT and ELT events were counted up in different stations, and the characteristics of their spatio-temporal distribution were diagnosed at last. The study drew following conclusions： 1） The consistent anomaly distribution characteristic was the most important mode of the EHT and ELT events in Northwest China. 2） The spatial distribution of the EHT and ELT events can be divided into five sub-regions, namely, the north of Qinghai and west of Gansu, the north of Xinjiang, the south of Xinjiang, the east of Northwest China and the south of Qinghai. 3） The EHT events showed remarkable increasing trend in all of five sub-regions, but only in the north of Qinghai and west of Gansu area, sudden change phenomenon occurred; the ELT events showed decreasing trend in all of five sub-regions, and sudden change phenomenon occurred in Northwest China except for south of Qinghai. 4） In all of five sub-regions the EHT events showed remarkable 12-14yr period oscillation, and the ELT event showed significant 13-15yr and 7-8yr period oscillation. 5） The EHT and ELT events displayed remarkable positive and negative responses to regional warming of Northwest China respectively.     

Stochastic Model for Estimating Extreme Water Level in Port and Coastal Engineering Design

Extreme water level is an important consideration when designing coastal protection structures. However, frequency analysis recommended by standard codes only considers the annual maximum water level, whereas water levels should actually be regarded as a combination of astronomical tide and storm surge. The two impacting factors are both random variables, and this paper discusses their dependency structures and proposes a new joint probability method to determine extreme design water levels. The lognormal, Gumbel, Weibull, Pearson type 3, traditional maximum entropy, and modified maximum entropy distributions are applied to fit univariate data of astronomical tides and storm surges separately, and the bivariate normal, Gumbel-Hougaard, Frank and Clayton copulas are then utilized to construct their joint probability distributions. To ensure that the new design method is suitable for use with typhoon data, the annual occurrence frequency of typhoon processes is considered and corresponding bivariate compound probability distributions are proposed. Based on maximum water level data obtained from Hengmen hydrological station in the Pearl River Basin, China, these probability models are applied to obtain designs for extreme water levels using the largest sum of the astronomical tide and storm surge obtained under fixed joint return periods. These design values provide an improved approach for determining the necessary height of coastal and offshore structures.     

昆仑山提孜那甫河流域雨雪分离的温度条件分析

气候变暖背景下高海拔山区融雪（冰）以及强降水引发的洪水愈加难以预测,通过山区雨雪分离可判定引发洪水的温度条件,从而为山洪准确预报提供简单而科学的参考依据。本研究以昆仑山提孜那甫河流域为例,基于流域内不同海拔气象站2012-2016年的降水以及温度数据,结合MOD10A2积雪数据,采用温度积分法和概率统计方法,利用研究期内的平均温度,确定出不同降水形态对应的温度条件,以达到雨雪分离的目的。研究结果表明,莫木克站最大温和积温分别达到20.91 ℃和51.82 ℃时,降水可判定为降雨,最大温和积温分别低于18.13 ℃,43.69 ℃时,降水可判定为降雪;库地站最大温和积温分别达到14.51 ℃,33.17 ℃时,降水可判定为降雨,最大温和积温分别低于13.57 ℃,31.68 ℃时,降水可判定为降雪;西合休站最大温和积温分别达到9.43 ℃,19.53 ℃时,降水可判定为降雨,最大温和积温分别低于8.22 ℃,19.4 ℃时,降水可判定为降雪。利用流域内气象站点附近乡镇的气象统计数据对温度条件及分离结果进行验证,在海拔2000 m以下、2000~3000 m以及3000 m以上不同海拔地区的准确率分别为92.86%、79.49%以及88.3%。本研究可为判别洪水类型和洪水预报提供科学参考。     

基于CMIP6的中国未来高温危险性变化评估

评估高温灾害的危险性变化,能够为区域高温灾害风险管理和制定减灾措施提供决策依据。本研究选取高温日数、最高温度和平均高温强度3个指标,基于1961—2020年中国2517个气象站点日最高温数据和CMIP6情景模式比较计划中SSP2-4.5情景下12个气候模式提供的2031—2099年未来气候预测数据集,用核密度概率估计方法计算了4个重现期（即5、10、20和50年）下3个指标的取值,对中国未来高温危险性变化进行了评估。结果表明：① 在SSP2.4-5情景下,中国的高温日数呈现出4个危险中心,分别是：西北干旱（半干旱）地区中部、华北和华中地区的交汇区域、西南地区中部和华南地区南部,并且高温日数从这4个中心向外逐渐减少;最高温度在空间上的分布北部大于南部,东部大于西部。平均高温强度的分布则呈现出从华北地区南部、西北干旱（半干旱）地区西部和东部地区西部向我国除青藏高原地区外的其它地区减少的趋势; ② 在SSP2.4-5情景下,随着重现期年限的增长,中国地区3个高温指标均呈增长趋势且增幅较大,并且高值范围也在不断扩大;③ 3个高温指标变化值均呈现出了明显的空间聚集性,3个指标共同显示的热点区域包括西南地区北部和南部、西北干旱（半干旱）地区中部和华北、华中地区的少部分区域,这些地区发生高温灾害的可能最大,同时根据高温日数变化和最高温度变化,东部地区西部发生高温灾害可能也较大,3个指标共同显示的冷点区域包括青藏高原地区东南部、西北干旱（半干旱）地区的西部和我国东南沿海地区,这些地区几乎不会发生高温危险。     

降雨事件对上海地铁通勤客流时空影响的精细尺度研究

全球气候变化背景下,降雨事件日益增多,严重影响城市交通和居民的日常出行。本文以上海市为例,基于分时降雨数据和地铁OD客流数据,运用Prophet时序模型拟合降雨事件下的客流常态值,从站点和OD二个维度定量评估降雨造成的地铁通勤客流变化时空格局。研究结果表明：① 通勤客流总体随小时雨量增大而下降,不同类型站点客流的降雨波动性呈现差异;降雨会造成进站客流的时间滞后性和堆积性,通勤出行需求越大的站点类型堆积效应越显著;由于出发时间弹性差异,不同时点客流的降雨敏感性也不同,7:00和17:00敏感性较高,8:00—9:00和18:00—19:00则相对刚性;② 降雨会造成行程时间≤15 min的短距离客流显著上升,总体增加7.3%,中长距离客流变化不明显,总体减少1.3%;在不同功能区之间,早高峰居住型→产业型的客流波动和时间堆积性最为显著,晚高峰商服型→居住型的返程客流波动性较低;早高峰降雨敏感性线路的起始站点多分布在大型居住区,晚高峰则位于大型产业园区和商业中心;晚高峰返程客流的波动性低于早高峰。尽管降雨事件对通勤客流总量影响不明显,但会造成局部空间区域和时点的客流激增。本文的研究方法与结果有助于量化降雨对地铁通勤客流的影响程度,并为空间化的交通运行保障提供决策依据。     

基于泊松分布的川东暴雨概率特征分析

暴雨是川东地区主要的气象灾害之一,对经济建设有重大影响。为进一步揭示该地区暴雨的统计特征,利用川东地区有代表性的4个测站（重庆、达州、巴中、南充）47年间（1961-2007年）4-10月日降水量资料,借助于泊松分布模式对该地区暴雨概率特征进行了分析。结果表明：用泊松分布模式能很好地描述川东地区的暴雨概率分布特征;模式计算均得出所研究的4站每年出现3次暴雨的机率最大。     

日降水量的空间插值方法与应用对比分析——以深圳市为例

综合分析了四种空间插值方法,即距离权重倒数法、局部多项式法、普通克里金法和考虑海拔的协克里金法的特点,并以深圳市36个雨量站2006年雨季27天的日累计降水量数据为实例进行了研究和验证,采用交叉检验的方法对插值结果进行比较。研究表明,四种方法均能反映降水总体情况,但插值曲面相对真实曲面较平滑,距离权重倒数法的插值曲面最为平滑;多项指标比较显示,克里金法优于距离权重倒数法和局部多项式法。与普通克里金法相比,考虑海拔的协克里金法对插值精度没有明显提高。依照雨量站海拔、日均降水量分别对插值结果数据分组统计比较表明,海拔高的雨量站插值结果普遍大于实测结果,海拔低的雨量站则相反;日均降水量较大时(>50mm),插值误差明显增大。     

Trends in temperature and precipitation extremes over Circum-Bohai-Sea region, China

Trends in temperature and precipitation extremes from 1961 to 2008 have been investigated over Circum-Bohai-Sea region,China using daily temperature and precipitation data of 63 meteorological stations.The re-sults show that at most stations,there is a significant increase in the annual frequency of warm days and warm nights,as well as a significant decrease in the annual frequency of cold days,cold nights,frost days,and annual diurnal temperature range(DTR).Their regional averaged changes are 2.06 d/10yr,3.95 d/10yr,-1.88 d/10yr,-4.27 d/10yr,-4.21 d/10yr and-0.20℃/10yr,respectively.Seasonal changes display similar patterns to the annual results,but there is a large seasonal difference.A significant warming trend is detected at both annual and seasonal scales,which is more contributed by changes of indices defined by daily minimum temperature than those defined by daily maximum tem-perature.For precipitation indices,the regional annual extreme precipitation displays a weak decrease in terms of magnitude and frequency,i.e.extreme precipitation days(RD95p),intensity(RINTEN),proportion(RPROP) and maximum consecutive wet days(CWD),but a slight increase in the maximum consecutive dry days(CDD),which are consistent with changes of annual total precipitation(PRCPTOT).Seasonally,PRCPTOT and RD95p both exhibit an increase in spring and a decrease in other seasons with the largest decrease in summer,but generally not significant.In summary,this study shows a pronounced warming tendency at the less rainy period over Circum-Bohai-Sea region,which may affect regional economic development and ecological protection to some extent.     

Long-term variation of storm surge-associated waves in the Bohai Sea

When investigating the long-term variation of wave characteristics as associated with storm surges in the Bohai Sea, the Simulating Waves Nearshore(SWAN) model and ADvanced CIRCulation(ADCIRC) model were coupled to simulate 32 storm surges between 1985 and 2014. This simulation was validated by reproducing three actual wave processes, showing that the simulated significant wave height(SWH) and mean wave period agreed well with the actual measurements. In addition, the long-term variations in SWH, patterns in SWH extremes along the Bohai Sea coast, the 100-year return period SWH extreme distribution, and waves conditional probability distribution were calculated and analyzed. We find that the trend of SWH extremes in most of the coastal stations was negative, among which the largest trend was-0.03 m/a in the western part of Liaodong Bay. From the 100-year return period of the SWH distribution calculated in the Gumbel method, we find that the SWH extremes associated with storm surges decreased gradually from the center of the Bohai Sea to the coast. In addition, the joint probability of wave and surge for the entire Bohai Sea in 100-year return period was determined by the Gumbel logistic method. We therefore, assuming a minimum surge of one meter across the entire Bohai Sea, obtained the spatial SWH distribution. The conclusions of this study are significant for offshore and coastal engineering design.