A multi-distribution approach to POT methods for determining extreme wave heights     

Franck Mazas  Luc Hamm 《Coastal Engineering》2011

Determination of extreme wave heights using a Peaks-Over-Threshold (POT) approach is revisited. Firstly, the GPD-Poisson model is recalled. A double threshold is presented and justified, with objective tools for determining the high threshold. This model is then extended to other statistical distributions, namely the Weibull and Gamma distributions. Objective criteria (BIC and AIC) based upon likelihood are used to select the best-fitting distribution. This method is tested on two locations: the historical IAHR Haltenbanken dataset and a location at the entry of the Strait of Gibraltar. Finally, sensitivity analyses are carried out with respect to the high threshold and to the duration of the dataset to estimate the robustness of the approach presented.  相似文献   

Trade-offs between physical risk and economic reward affect fishers’ vulnerability to changing storminess     

《Global Environmental Change》2021

Climate change-driven alterations in storm frequency and intensity threaten the wellbeing of billions of people who depend on fisheries for food security and livelihoods. Weather conditions shape vulnerability to both loss of life and reduced fishing opportunities through their influence on fishers' daily participation decisions. The trade-off between physical risk at sea and the economic rewards of continued fishing under adverse weather conditions is a critical component of fishers’ trip decisions but is poorly understood. We employed a stated choice experiment with skippers from a temperate mixed-species fishery in southwest England to empirically assess how fishers trade off the risks from greater wind speed and wave height with the benefits of expected catch and prices. Technical fishing and socio-economic data were collected for individual fishers to identify the factors influencing trade-off decisions. Fishers preferred increased wind speed and wave height up to a threshold, after which they became increasingly averse to worsening conditions. Fishing gear, vessel length, presence of crew, vessel ownership, age, recent fishing success and reliance on fishing income all influenced the skippers’ decisions to go to sea. This study provides a first insight into the socio-economic, environmental, and technical fishing factors that can influence the sensitivity of individual fishers to changing storminess. These insights can help to inform fisheries climate vulnerability assessments and the development of adaptation measures.  相似文献   

极值理论在地震危险性分析中的应用与研究   总被引：9，自引：1，他引：9  

张卫东  李茂林  张秀梅  王九洋 《东北地震研究》2005,21(1):24-30

本文对极值方法的Ⅰ-Ⅲ型和Ⅰ型修正式四种分布模型以及在地震应用过程中的识别方法、参数估计、检验方法、应用范围和预测效果等进行了研究和探讨；对各模型与实际资料偏离程度和存在的问题给出了基本估计；对模型类型的选择给出了两种较实用的检验方法和应用上的一些具体的建议。为拓展极值方法在地震危险性分析中的应用范围，本文还给出了13种与地震预报有关的公式和预报方法。  相似文献   

Performance of Multi Model Canonical Correlation Analysis (MMCCA) for prediction of Indian summer monsoon rainfall using GCMs output     

Ankita Singh  Nachiketa Acharya  Uma Charan Mohanty  Gopbandhu Mishra 《Comptes Rendus Geoscience》2013,345(2):62-72

The emerging advances in the field of dynamical prediction of monsoon using state-of-the-art General Circulation Models (GCMs) have led to the development of various multi model ensemble techniques (MMEs). In the present study, the concept of Canonical Correlation Analysis is used for making MME (referred as Multi Model Canonical Correlation Analysis or MMCCA) for the prediction of Indian summer monsoon rainfall (ISMR) during June-July-August-September (JJAS). This method has been employed on the rainfall outputs of six different GCMs for the period 1982 to 2008. The prediction skill of ISMR by MMCCA is compared with the simple composite method (SCM) (i.e. arithmetic mean of all GCMs), which is taken as a benchmark. After a rigorous analysis through different skill metrics such as correlation coefficient and index of agreement, the superiority of MMCCA over SCM is illustrated. Performance of both models is also evaluated during six typical monsoon years and the results indicate the potential of MMCCA over SCM in capturing the spatial pattern during extreme years.  相似文献   

中国干旱半干旱区洪涝灾害的初步分析   总被引：5，自引：1，他引：5  

黄建平  冉津江  季明霞 《气象学报》2014,72(6):1096-1107

中国干旱半干旱区的洪涝灾害是一个尚未引起人们重视的重大科学问题,这主要是因为干旱半干旱区对洪涝灾害的防范意识比较薄弱。而极端降水事件的次数、强度和持续时间与干旱半干旱区的洪涝灾害有密切联系,直接影响该区域洪涝灾害及其次生地质灾害的次数与严重程度。以干旱半干旱区的极端降水事件为切入点,分析了中国干旱半干旱区的极端降水事件次数和极端降水量的变化特征,旨在为干旱半干旱区的洪涝灾害研究提供科学依据。结果表明,进入21世纪以来,中国110°E以西的干旱半干旱区极端降水事件的日数有所增多,而110°E以东的区域日数都有所减少。干旱半干旱区极端降水量的变化也呈现出西增东减的分布,大部分干旱半干旱区的极端降水量变化占总降水量变化的40%以上,一部分地区能达到50%,甚至100%-200%。从季节变化来看,春季天山以北、新疆南部、甘肃敦煌和内蒙古包头以北地区极端降水量增加较多,夏季110°E以西的干旱半干旱区极端降水量均增大明显,秋季陕西榆林、内蒙古鄂尔多斯、包头和呼和浩特等地极端降水量增大较明显。  相似文献   

Spatial downscaling of TRMM precipitation data based on the orographical effect and meteorological conditions in a mountainous area     

《Advances in water resources》2013

The lack of high resolution precipitation data has posed great challenges to the study and management of extreme rainfall events. Satellite-based rainfall products with large areal coverage provide a potential alternative source of data where in situ measurements are not available. However, the mismatch in scale between these products and model requirements has limited their application and demonstrates that satellite data must be downscaled before being used. This study developed a statistical spatial downscaling scheme based on the relationships between precipitation and related environmental factors such as local topography and pre-storm meteorological conditions. The method was applied to disaggregate the Tropical Rainfall Measuring Mission (TRMM) 3B42 products, which have a resolution of 0.25° × 0.25°, to 1 × 1 km gridded rainfall fields. The TRMM datasets in accord with six rainstorm events in the Xiao River basin were used to validate the effectiveness of this approach. The downscaled precipitation data were compared with ground observations and exhibited good agreement with r² values ranging from 0.612 to 0.838. In addition, the proposed approach provided better results than the conventional spline and kriging interpolation methods, indicating its promise in the management of extreme rainfall events. The uncertainties in the final results and the implications for further study were discussed, and the needs for additional rigorous investigations of the rainfall physical process prior to institutionalizing the use of satellite data were highlighted.  相似文献   

MM5V3模式对IPCCA1B情景下中国地区极端事件的模拟和预估   总被引：1，自引：1，他引：0       下载免费PDF全文

胡伯彦  汤剑平  王淑瑜 《地球物理学报》2013,56(7):2195-2206

利用MM5V3区域气候模式单向嵌套ECHAM5全球环流模式,对中国地区1978-2000年及IPCC A1B情景下2038-2070年气候分别进行了水平分辨率为50 km的模拟试验.文章首先检验了模式模拟的当代极端气候结果,在此基础上对6个极端温度指数和6个极端降水指数的未来变化进行了预估.检验结果表明:MM5V3模式对中国地区当代日最高、最低温度及强降水(大雨和暴雨)日数的空间分布和概率特征均具有一定的模拟能力,但模拟的日最高温度在大部分地区偏低,日最低温度在南方地区偏低、西北地区偏高.概率统计结果显示日最高温度向低值频段偏移,日最低温度在0℃的峰值附近明显偏高.模式对大雨和暴雨年平均日数的模拟在东部地区偏多,概率统计结果则为一致偏大.未来中国地区极端气候预估结果表明:极端高温、极端低温和相对高温在全国范围内都将升高,且线性趋势均为上升;霜日日数则为减少,并具有下降趋势;暖日日数和相对低温在青藏高原和新疆部分地区有所减少、其它地区均为增加,且线性趋势暖日日数为上升,相对低温不明显.极端降水指数的变化具有区域特征,其中单日最大降水、连续五日最大降水、最长无雨期、强降水日数、简单降水强度和极端降水总量均在江淮、华南及西南地区有所增多,而在东北及内蒙古地区有所减少,未来中国南方地区降水的极端化趋势将更加显著.极端降水指数的线性趋势除最长无雨期外其它均为上升.  相似文献   

胡杨根系分布特征与根系吸水模型建立   总被引：16，自引：1，他引：15  

冯起  司建华  李建林  席海洋 《地球科学进展》2008,23(7):765-772

依据2006年和2007年6~7月在极端干旱区额济纳的实测资料,利用分形和概率统计的方法对胡杨根系分布与根区土壤水分的关系进行了分析研究。引入土壤含水率期望(cm·g/g)的概念,建立了含水率期望值与根系分维值之间的函数关系,并求出了适宜胡杨生长的土壤含水率期望值的范围。同时建立了初版的根系吸水模型,并进行验证,得到较好的结果。  相似文献   

融合土地覆盖和土壤水分产品的近地表空气温度空间化方法     

高亮  杜鑫  李强子  王红岩  张源  王思远 《地球信息科学学报》2020,22(10):2023-2037

空气温度是评价人居环境的重要指标,与人类的生产生活息息相关;其观测对于水文、环境、生态和气候变化等方面的研究具有重要意义。传统的大范围空气温度观测数据一般通过气象站点获取,但由于气象观测站点空间分布离散稀疏的特点,所获取的数据不能精确描述空间连续的空气温度变化情况。因此,实现基于遥感数据的近地表空气温度精准估算具有重要的现实意义。本研究基于精细的地表覆盖类型、空间连续的土壤水分、地表温度（LST）数据,并结合其他辅助数据,构建了近地表空气温度空间化模型,并对近地表空气温度影响因子进行评估,发现地表覆盖类型对近地表空气温度的影响最大,土壤水分为最活跃的影响因素,经验证,模型精度较高,R²接近0.85,RMSE为0.5℃。本研究获取的精确空间连续的近地表空气温度信息,能够充分表达其空间异质性,为农业气象灾害灾变过程监测、农作物生长过程模拟、区域气候变化分析等研究提供良好的近地表空气温度数据支撑。  相似文献   

冬奥会复杂山地百米尺度10m风速预报的机器学习订正对比试验     

徐景峰  宋林烨  陈明轩  杨璐  韩雷 《大气科学》2023,(3):805-824

本文以传统机器学习算法XGBoost和深度学习算法CU-Net为基础,针对北京快速更新无缝隙融合与集成预报系统（RISE系统）预报的北京冬奥会延庆及张家口赛区100米分辨率的冬季近地面10 m风速数据,进行每日逐小时起报的未来逐6小时间隔的冬奥高山站点及其周边地区风速预报偏差订正方法研究和对比分析。对于站点订正,首先将RISE系统预测的10 m风速插值到对应的自动气象站站点,然后根据风速等级表归类,针对每个分类单独构建XGBoost模型,每个区间模型合并后形成L-XGBoost,使用均方根误差和预报准确率作为评分标准,结果表明风速归类的L-XGBoost算法订正效果比不归类的原始XGBoost模型有一定提升,说明在传统机器学习中加入归类方法有助于改善复杂山地站点风速预报技巧。对于站点及其周边地区风速订正,本文在CUNet模型基础上,通过引入不同深度的CU-Net子网络,构建了新的算法模型CU-Net++,并考虑了预报日变化误差和复杂地形对10 m风速的影响,以自动气象站为中心构建空间小区域样本数据,对RISE系统风速预报偏差进行订正。试验结果表明,CU-Net和CU-Net++均可以充...  相似文献