Color map design for visualization in flood risk assessment

Visualizations of flood maps from simulation models are widely used for assessing the likelihood of flood hazards in spatial planning. The choice of a suitable type of visualization as well as efficient color maps is critical to avoid errors or bias when interpreting the data. Based on a review of previous flood uncertainty visualization techniques, this paper identifies areas of improvements and suggests criteria for the design of a task-specific color scale in flood map visualization. We contribute a novel color map design for visualizing probabilities and uncertainties from flood simulation ensembles. A user study encompassing 83 participants was carried out to evaluate the effects of this new color map on user’s decisions in a spatial planning task. We found that the type of visualization makes a difference when it comes to identification of non-hazardous sites in the flood risk map and when accepting risks in more uncertain areas. In comparison with two other existing visualization techniques, we observed that the new design was superior both in terms of task compliance and efficiency. In regions with uncertain flood statuses, users were biased toward accepting less risky locations with our new color map design.     

ENSEMBLE PREDICTION EXPERIMENTS OF TYPHOON TRACK BASED ON THE STOCHASTIC TOTAL TENDENCY PERTURBATION

The GRAPES-TCM is used to make ensemble prediction experiments for typhoon track. Three kinds of ensemble schemes are designed for the experiments. A total of 109 experiments are made for the nine typhoons in 2011 and the integral time is 72 h. The experiment results are shown as follows. In the three ensemble schemes, on the whole, scheme 1 has the best track prediction. Its average absolute track error and overall deviations of typhoon moving speed and moving direction are all the smallest in the three schemes. For both scheme 1 and scheme 2, they are all smaller than those of their control predictions. Both of their ensemble predictions show superiority to their deterministic predictions. Overall, compared with the observations, the typhoon moving directions of the three schemes mainly skew to the right, and in the late integration they mainly tend to be relatively slow. In the three schemes, the track dispersion of scheme 1 is the largest and that of scheme 3 the smallest. In scheme 1 it is much larger than in schemes 2 and 3. The difference of dispersion between scheme 2 and scheme 3 is small. The track dispersions of the three schemes are all much smaller than their rational dispersions. Compared with the eight domestic and overseas operational numerical weather prediction (NWP) models, scheme 1 has better predictions than the other seven operational models except ECMWF NWP model. Scheme 1 has the value of operational application.     

中期数值天气预报业务的回顾与展望

本文回顾了近年来国内外中期数值天气预报业务的新进展,简略地介绍了当今国外（以欧洲中期天气预报中心为主）和我国中期数值天气预报业务系统。最后对未来中期数值天气预报的发展作一展望,指出其未来发展的主要方向。     

太湖叶绿素a同化系统敏感性分析

太湖叶绿素a同化系统对于不同参数的敏感性将直接影响到该系统能否精确的估算太湖叶绿素a的浓度分布.利用2009年4月21日环境一号卫星(HJ-1B CCD2)影像数据反演太湖叶绿素a浓度场信息.以此作为背景场信息,结合基于集合均方根滤波的太湖叶绿素a同化系统,分析和评价了样本数目、同化时长、背景场误差、观测误差和模型误差对于同化系统性能的影响.结果表明:从计算成本、系统运行时间和同化效果等方面分析,当集合样本数目达到30~40左右时同化系统取得了较好的结果;同化系统对于背景场误差的估计变化不是很敏感,即初始场的估计是否准确对于同化系统的性能影响不是很大;同化系统对于模型误差和观测误差的变化较为敏感,不同的测试点位由于水体动力学性质不一,其敏感性的表现形式有所差异;利用数据同化方法可以有效地估算太湖叶绿素a浓度.     

Geophysical flows under location uncertainty,Part I Random transport and general models

A stochastic flow representation is considered with the Eulerian velocity decomposed between a smooth large scale component and a rough small-scale turbulent component. The latter is specified as a random field uncorrelated in time. Subsequently, the material derivative is modified and leads to a stochastic version of the material derivative to include a drift correction, an inhomogeneous and anisotropic diffusion, and a multiplicative noise. As derived, this stochastic transport exhibits a remarkable energy conservation property for any realizations. As demonstrated, this pivotal operator further provides elegant means to derive stochastic formulations of classical representations of geophysical flow dynamics.     

Geophysical flows under location uncertainty,Part II Quasi-geostrophy and efficient ensemble spreading

Models under location uncertainty are derived assuming that a component of the velocity is uncorrelated in time. The material derivative is accordingly modified to include an advection correction, inhomogeneous and anisotropic diffusion terms and a multiplicative noise contribution. In this paper, simplified geophysical dynamics are derived from a Boussinesq model under location uncertainty. Invoking usual scaling approximations and a moderate influence of the subgrid terms, stochastic formulations are obtained for the stratified Quasi-Geostrophy and the Surface Quasi-Geostrophy models. Based on numerical simulations, benefits of the proposed stochastic formalism are demonstrated. A single realization of models under location uncertainty can restore small-scale structures. An ensemble of realizations further helps to assess model error prediction and outperforms perturbed deterministic models by one order of magnitude. Such a high uncertainty quantification skill is of primary interests for assimilation ensemble methods. MATLAB^® code examples are available online.     

全球温升1.5℃和2.0℃情景下中国降雨诱发地质灾害危险性和人口暴露度评估研究

气候变化情景下极端降水事件的频次和强度预估呈增加趋势,这会导致全球部分地区极端降雨诱发地质灾害风险的增加。本文基于中国降雨诱发地质灾害易发性模型和不同地貌分区的累积事件降雨量-降雨历时阈值曲线,采用最新的CMIP6全球气候模式多模式集合结果,基于全球温升目标情景的视角,从地质灾害空间易发性和发生频次两方面,探讨温升情景下中国地质灾害危险性的可能变化及其对暴露人口的潜在影响。结果表明,CMIP6多模式集合预估的多年平均降水在温升1.5℃和2.0℃情景下相比基准时期可能增加5.4%～9.5%,导致中等至极高地质灾害易发区范围预估增加0.33%～0.74%,由于预估的极端降水事件增加,地质灾害发生频次预估增加7.0%～11.2%,进一步综合未来人口空间分布,潜在地质灾害暴露人口可能增加6.20亿人次（18.90%）和4.26亿人次（12.97%）。各地貌分区未来情景下地质灾害危险性预估增加且存在显著的空间异质性,温升2.0℃情景下中等至极高易发性范围相比基准时期增加0.71%～1.28%,地质灾害发生频次预估增加1.2%～15.6%,其中,青藏高原区地质灾害危险性增加最明显。综合考虑未来人口...     

基于集合卡尔曼变换的区域集合预报初步研究

为了深入研究集合卡尔曼变换(Ensemble Transform Kalman Filter,ETKF)初值扰动方法,提高集合预报质量,从全球大集合预报资料中提取初始扰动场,建立区域模式的ETKF初值扰动方案,对2008年7月22日发生在中国东部的一次暴雨过程进行集合预报试验,并分析ETKF方案构造的扰动场特征和集合预报效果。结果表明,由ETKF初始扰动方案产生的扰动场大小与分布合理,能够反映观测站点的空间分布,能够保持所有正交、不相关方向的误差方差。集合预报降水落区相对控制预报有所改善,集合平均小雨和中雨TS评分和BS评分总体优于控制预报。24h集合预报的Talagrand分布优于36h预报。试验结果揭示了ETKF初值扰动方案的基本性质及利用ETKF方法进行区域集合预报的可行性。     

地区场选样洪水计算在西部流域应用分析

为采用地区场选样洪水计算方法分析研究建立了西部祖厉河流域设计洪水计算经验公式,设计计算成果经与皮尔逊三型频率曲线设计计算成果比较分析,计算成果精度较高。由此确定了该流域设计洪水计算相关成果图及查算表,为该流域设计洪水计算提供技术支撑。     

集合数值天气预报的研究进展

集合预报是目前国外广泛应用的一种新的数值预报技术,国内由于计算条件的限制,集合预报的研究应用起步较晚,目前虽已取得了一些研究成果,但还没有广泛的应用到实际的业务预报之中。集合预报的应用,在天气预报上主要是概率预报,另外在“目标观测”、资料同化等方面也有广泛应用。集合概率预报的一系列适用的验证,增加了概率预报的信度。