CoSMoS (Coastal Storm Modeling System) Southern California v3.0 Phase 2 ocean-currents projections: 1-year storm in San Diego County

Projected Hazard: Model-derived ocean current velocities (in meters per second) for the given storm condition and sea-level rise (SLR) scenario. Model Summary: The Coastal Storm Modeling System (CoSMoS) makes detailed predictions (meter-scale) over large geographic scales (100s of kilometers) of storm-induced coastal flooding and erosion for both current and future sea-level rise (SLR) scenarios. CoSMoS v3.0 for Southern California shows projections for future climate scenarios (sea-level rise and storms) to provide emergency responders and coastal planners with critical storm-hazards information that can be used to increase public safety, mitigate physical damages, and more effectively manage and allocate resources within complex coastal settings. Phase 2 data for Southern California include flood-hazard information for the coast from the border of Mexico to Pt. Conception. Several changes from Phase 1 projections are reflected in many areas; please read the model summary and inspect output carefully. Data are complete for the information presented. Details: Model background: The CoSMoS model comprises three tiers. Tier I consists of one Delft3D hydrodynamics FLOW grid for computation of tides, water level variations, flows, and currents and one SWAN grid for computation of wave generation and propagation across the continental shelf. The FLOW and SWAN models are two-way coupled so that tidal currents are accounted for in wave propagation and growth and conversely, so that orbital velocities generated by waves impart changes on tidal currents. The Tier I SWAN and FLOW models consist of identical structured curvilinear grids that extend from far offshore to the shore and range in resolution from 0.5 km in the offshore to 0.2 km in the nearshore. Spatially varying astronomic tidal amplitudes and phases and steric rises in water levels due to large-scale effects (for example, a prolonged rise in sea level) are applied along all open boundaries of the Tier I FLOW grid. Winds (split into eastward and northward components) and sea-level pressure (SLP) fields from CaRD10 (Dr. Dan Cayan, Scripps Institute of Oceanography, San Diego, California, written commun., 2014) that vary in both space and time are applied to all grid cells at each model time-step. Deep-water wave conditions, applied at the open boundaries of the Tier I SWAN model runs, were projected for the 21st century Representative Concentration Pathway (RCP) 4.5 climate scenario (2011-2100) using the WaveWatch III numerical wave model (Tolman and others, 2002) and 3-hourly winds from the GFDL-ESM2M Global Climate Model (GCM). Tier II provides higher resolution near the shore and in areas that require greater resolution of physical processes (such as bays, harbors, and estuaries). A single nested outer grid and multiple two-way coupled domain decomposition (DD) structured grids allow for local grid refinement and higher resolution where needed. Tier II was segmented into 11 sections along the Southern California Bight, to reduce computation time and complete runs within computational limitations. Water-level and Neumann time-series, extracted from Tier I simulations, are applied to the shore-parallel and lateral open boundaries of each Tier II sub-model outer grid respectively. Several of the sub-models proved to be unstable with lateral Neumann boundaries; for those cases one or both of the lateral boundaries were converted to water-level time-series or left unassigned. The open-boundary time-series are extracted from completed Tier I simulations so that there is no communication from Tier II to Tier I. Because this one-way nesting could produce erroneous results near the boundaries of Tier II and because data near any model boundary are always suspect, Tier II sub-model extents were designed to overlap in the along-coast direction. In the landward direction, Tier II DD grids extend to the 10-m topographic contour; exceptions exist where channels (such as the Los Angeles River) or other low-lying regions extend very far inland. Space- and time-varying wind and SLP fields, identical to those used in Tier I simulations, are applied to all Tier II DD grids to allow for wind-setup and local inverse barometer effects (IBE, rise or depression of water levels in response to atmospheric pressure gradients). A total of 42 time-series fluvial discharges are included in the Tier II FLOW domains in an effort to simulate exacerbated flooding caused by backflow at the confluence of high river seaward flows and elevated coastal surge levels migrating inland. Time-varying fluvial discharges are applied either at the closed boundaries or distributed as point sources within the relevant model domains. Wave computations are accomplished with the SWAN model using two grids for each Tier II sub-model: one larger grid covering the same area as the outer FLOW grid and a second finer resolution two-way coupled nearshore nested grid. The nearshore grid extends from approximately 800-1,000 m water depth up to 8-10 m elevations onshore. The landward extension is included to allow for wave computations of the higher SLR scenarios. Time- and space-varying 2D wave spectra extracted from previously completed Tier I simulations are applied approximately every kilometer along the open boundaries of the outer Tier II sub-model SWAN grids. The same space- and time-varying wind fields used in Tier I simulations are also applied to both Tier II SWAN grids to allow for computation of local wave generation. Tier III for the entire Southern California Bight consists of 4,802 cross-shore transects (CST) spaced approximately 100 m apart in the along-shore direction. The profiles extend from the -15 m isobath to at least 10 m above NAVD88. The CSTs are truncated for cases where a lagoon or other waterway exists on the landward end of the profile. Time-varying water levels and wave parameters (significant wave heights, Hs; peak periods, Tp; and peak incident wave directions, Dp), extracted from Tier II grid cells that coincide with the seaward end of the CSTs, are applied at the open boundary of each CST. The XBeach model is run in a hydrostatic (no vertical pressure gradients) mode including event-based morphodynamic change. Wave propagation, two-way wave-current interaction, water-level variations, and wave runup are computed at each transect. XBeach simulations are included in the CoSMoS model to account for infragravity waves that can significantly extend the reach of wave runup (Roelvink and others, 2009) compared to short-wave incident waves. The U.S. west coast is particularly susceptible to infragravity waves at the shore due to breaking of long-period swell waves (Tp > 15). Resulting water levels (WLs) from both Delft3D (high interest bays and marshes) and open-coast XBeach (CSTs) were spatially combined and interpolated to a 10 m grid. These WL elevations are differenced from the originating 2 m digital elevation model (DEM) to determine final flooding extent and depth of flooding. Events: The model system is run for pre-determined scenarios of interest such as the 1-yr or 100-yr storm event in combination with sea-level rise. Storms are first identified from time-series of total water level proxies (TWLpx) at the shore. TWLpx are computed for the majority of the 21st century (2010-2100), assuming a linear super-position of the major processes that contribute to the overall total water level. TWLpx time-series are then evaluated for extreme events, which define the boundary conditions for subsequent modeling with CoSMoS. Multiple 100-yr events are determined (varying Hs, Tp, Dp) and used for multiple model runs to better account for regional and directional flooding affects. Model results are combined and compiled into scenario-specific composites of flood projection. Digital Elevation Model (DEM): Our seamless, topobathymetric digital elevation model (DEM) was based largely upon the Coastal California TopoBathy Merge Project DEM, with some modifications performed by the USGS Earth Resources Observation and Science (EROS) Center to incorporate the most recent, high-resolution topographic and bathymetric datasets available. Topography is derived from bare-earth light detection and ranging (lidar) data collected in 2009-2011 for the CA Coastal Conservancy Lidar Project and bathymetry from 2009-2010 bathymetric lidar as well as acoustic multi- and single-beam data collected primarily between 2001 and 2013. The DEM was constructed to define the shape of nearshore, beach, and cliff surfaces as accurately as possible, utilizing dozens of bathymetric and topographic data sets. These data were used to populate the majority of the Tier I and II grids. To describe and include impacts from long-term shoreline evolution, including cumulative storm activity, seasonal trends, ENSO, and SLR, the DEM was modified for each SLR scenario. Long-term shoreline (Vitousek and Barnard, 2015) and cliff (Limber and others, 2015) erosion projections were efficiently combined along the cross-shore transects to evolve the shore-normal profiles. Elevation changes from the profiles were spatially-merged for a cohesive, 3D depiction of coastal evolution used to modify the DEM. These data are used to generate initial profiles of the 4,802 CSTs used for Phase 2 Tier III XBeach modeling and determining final projected flood depths in each SLR scenario. All data are referenced to NAD83 horizontal datum and NAVD88 vertical datum. Data for Tiers II and III are projected in UTM, zone 11. Outputs include: Projected ocean current velocities for the 100-year storm and 0.0 m sea-level rise scenario. Data correspond to the near-shore region including areas vulnerable to coastal flooding due to storm surge, sea-level anomalies, tide elevation, and wave run-up during the same storm and sea-level rise simulation. References Cited: Howell, S., Smith-Konter, B., Frazer, N., Tong, X., and Sandwell, D., 2016, The vertical fingerprint of earthquake cycle loading in southern California: Nature Geoscience, v. 9, p. 611-614, doi:10.1038/ngeo2741. Limber, P., Barnard, P.L. and Hapke., C., 2015, Towards projecting the retreat of California’s coastal cliffs during the 21st Century: in, Wang, P., Rosati, J.D., and Cheng, J., (eds.), The Proceedings of the Coastal Sediments: 2015, World Scientific, 14 p., doi:10.1142/9789814689977_0245 Roelvink, J.A., Reniers, A., van Dongeren, A.R., van Thiel de Vries, J., McCall, R., and Lescinski, J., 2009, Modeling storm impacts on beaches, dunes and barrier islands: Coastal Engineering, v. 56, p. 1,133–1,152, doi:10.1016/j.coastaleng.2009.08.006. Tolman, H.L., Balasubramaniyan, B., Burroughs, L.D., Chalikov, D.V., Chao, Y.Y., Chen H.S., Gerald, V.M., 2002, Development and implementation of wind generated ocean surface wave models at NCEP: Weather and Forecasting, v. 17, p. 311-333. Vitousek, S. and Barnard, P.L., 2015, A non-linear, implicit one-line model to predict long-term shoreline change: in, Wang, P., Rosati, J.D., and Cheng, J., (eds.), The Proceedings of the Coastal Sediments: 2015, World Scientific, 14 p., doi:10.1142/9789814689977_0215.预测灾害：对应给定风暴情景与海平面上升（Sea-Level Rise, SLR）情景的、由模型推导得到的海流流速（单位：米每秒）。 模型概述：海岸风暴模拟系统（Coastal Storm Modeling System, CoSMoS）可在数百公里级的大地理尺度上，以米级精度详细预测当前及未来海平面上升情景下，风暴诱发的海岸洪水与侵蚀。针对南加州的CoSMoS v3.0版本可针对未来气候情景（海平面上升与风暴）开展预测，为应急响应人员与海岸规划者提供关键风暴灾害信息，助力提升公共安全、减轻物理损失，并在复杂海岸环境中更高效地管理与调配资源。 第二阶段数据：南加州的相关数据涵盖了从墨西哥边境至康塞普西翁角（Pt. Conception）沿岸的洪水灾害信息。多个区域的预测结果与第一阶段相比存在多处调整，请仔细阅读模型概述并检查输出结果。本次展示的所有数据均完整有效。 模型细节： CoSMoS模型包含三个层级。第一层级（Tier I）包含一套用于计算潮汐、水位变化、水流与海流的Delft3D水动力FLOW网格，以及一套用于计算陆架区波浪生成与传播的SWAN波浪网格。FLOW与SWAN模型采用双向耦合模式，因此潮流会被纳入波浪传播与生长的计算过程，反之，波浪产生的轨道流速也会对潮流产生影响。第一层级的SWAN与FLOW网格采用完全一致的结构化曲线网格，覆盖从远海至近岸的区域，分辨率从远海的0.5公里逐步提升至近岸的0.2公里。在第一层级FLOW网格的所有开边界处，均施加了空间分布不均的天文潮汐振幅与相位，以及由大尺度效应（例如长期海平面上升）引发的水位热膨胀增量。每个模型时间步内，所有网格单元均会加载由CaRD10（加州大学圣地亚哥分校斯克里普斯海洋研究所Dan Cayan博士，2014年私人通信）提供的、时空均变化的风场（分解为东向与北向分量）与海平面气压（SLP）场。针对第一层级SWAN模型开边界的深水波浪条件，本研究采用WaveWatch III数值波浪模式（Tolman等，2002）与GFDL-ESM2M全球气候模式（GCM）提供的3小时分辨率风场，针对21世纪典型浓度路径（Representative Concentration Pathway, RCP）4.5情景（2011-2100年）开展了投影。 第二层级（Tier II）可在近岸及需要更高分辨率物理过程模拟的区域（例如海湾、港口与河口）提供更高的网格分辨率。本层级采用一套嵌套外网格与多套双向耦合的区域分解（DD）结构化网格，可在需要的区域实现局部网格加密与更高分辨率。第二层级沿南加州湾被划分为11个区段，以降低计算量并在算力限制内完成模拟。 从第一层级模拟结果中提取的水位与诺依曼时间序列，分别加载至各第二层级子模型外网格的沿岸平行开边界与侧向开边界。部分子模型在侧向诺依曼边界条件下出现了不稳定情况，针对此类情形，需将一个或两个侧向边界转换为水位时间序列，或保留为未赋值状态。由于开边界时间序列均从已完成的第一层级模拟结果中提取，第二层级与第一层级之间不存在数据交互。鉴于这种单向嵌套模式可能在第二层级边界附近产生误差，且任何模型边界附近的数据均存在不确定性，第二层级子模型的范围在沿岸方向设置为相互重叠。在陆地方向，第二层级区域分解网格延伸至10米地形等高线，仅在洛杉矶河等河道或其他低洼区域延伸至更远内陆的情况除外。所有第二层级区域分解网格均加载与第一层级模拟完全一致的时空变化风场与SLP场，以模拟风增水与局部逆气压效应（IBE，即大气压强梯度引发的水位升降）。 为模拟河流向海径流与沿岸风暴潮水位升高共同引发的回流加剧洪水，第二层级FLOW网格中共包含42套河流径流时间序列。时变河流径流量可加载至闭合边界，或作为点源分布至相关模型区域内。 波浪计算采用SWAN模型，每个第二层级子模型均配有两套网格：一套覆盖范围与外FLOW网格一致的大尺度网格，以及一套分辨率更高的双向耦合近岸嵌套网格。近岸网格的覆盖范围从约800-1000米水深区域延伸至陆上8-10米高程区域，该陆地方向延伸范围可支持更高海平面上升情景下的波浪计算。从已完成的第一层级模拟结果中提取的时空变化二维波浪谱，每隔约1公里加载至第二层级子模型外SWAN网格的开边界处。与第一层级模拟一致的时空变化风场，同样会加载至两套第二层级SWAN网格，以实现局部波浪生成的计算。 第三层级（Tier III）覆盖整个南加州湾，包含4802条跨岸断面（CST），断面间距在沿岸方向约为100米。断面从-15米等深线延伸至至少北美垂直基准面1988（NAVD88）以上10米的区域，若断面陆端存在泻湖或其他水道，则会对断面进行截断。从与跨岸断面向海端重合的第二层级网格单元中提取的时变水位与波浪参数（有效波高Hs、峰值周期Tp与入射波峰值方向Dp），会加载至每条跨岸断面的开边界处。XBeach模型采用静水压模式（不考虑垂直压强梯度），并包含基于事件的地形动力变化。每个断面上均会计算波浪传播、双向波流相互作用、水位变化与波浪爬高。 CoSMoS模型中加入XBeach模拟，以考虑亚重力波的影响：相较于短周期入射波，亚重力波可显著提升波浪爬高的影响范围（Roelvink等，2009）。由于长周期涌浪（Tp>15秒）的破碎，美国西海岸沿岸区域对亚重力波尤为敏感。 将Delft3D模型（高关注海湾与沼泽区域）与开放海岸XBeach模型（跨岸断面）得到的最终水位（WLs）进行空间合并与插值，生成10米分辨率的网格。将这些水位高程与原始2米分辨率数字高程模型（DEM）做差值计算，即可得到最终的洪水范围与洪水深度。 模拟事件：本模型系统针对预定义的感兴趣情景开展模拟，例如结合海平面上升的1年一遇或100年一遇风暴事件。首先从沿岸总水位代理（TWLpx）时间序列中识别风暴。总水位代理时间序列的计算覆盖了21世纪的大部分时段（2010-2100年），假设贡献总水位的主要过程满足线性叠加原则。随后对总水位代理时间序列进行极端事件识别，以此作为后续CoSMoS模拟的边界条件。本研究确定了多组100年一遇风暴事件（有效波高、峰值周期与入射方向各不相同），并开展多组模型模拟，以更全面地考虑区域与方向对洪水的影响。将所有模型结果合并并整理为针对特定情景的洪水预测合成结果。 数字高程模型（DEM）：本研究的无缝地形水深数字高程模型主要基于加州海岸地形水深合并项目DEM，美国地质调查局地球资源观测与科学（EROS）中心对其进行了部分修改，以纳入最新的高分辨率地形与水深数据集。地形数据来自2009-2011年加州海岸保护局激光雷达（lidar）项目采集的裸地激光雷达数据，水深数据则来自2009-2010年的水深激光雷达数据，以及2001-2013年采集的声学多波束与单波束测深数据。本DEM旨在尽可能精准地刻画近岸、海滩与崖岸的地形形态，整合了数十套水深与地形数据集。这些数据被用于填充第一与第二层级的大部分网格。为描述并纳入长期海岸线演变的影响（包括累积风暴活动、季节趋势、厄尔尼诺南方涛动与海平面上升），本DEM针对每个海平面上升情景均进行了修改。研究人员将长期海岸线（Vitousek与Barnard，2015）与崖岸（Limber等，2015）侵蚀预测结果沿跨岸断面进行高效整合，以更新岸垂向剖面。将剖面得到的高程变化进行空间合并，得到连贯的海岸演变三维可视化结果，用于修改DEM。这些数据被用于生成第二阶段第三层级XBeach模拟所用的4802条跨岸断面的初始剖面，并用于确定每个海平面上升情景下的最终预测洪水深度。所有数据均采用北美水平基准面1983（NAD83）与北美垂直基准面1988（NAVD88）作为水平与垂直基准。第二与第三层级的数据采用通用横轴墨卡托投影第11带（UTM zone 11）进行投影。 输出数据包括：针对100年一遇风暴与0.0米海平面上升情景的预测海流流速。数据覆盖近岸区域，包括该风暴与海平面上升模拟期间，易受风暴潮、海平面异常、潮汐高程与波浪爬高影响的区域。 参考文献： 1. Howell, S., Smith-Konter, B., Frazer, N., Tong, X., and Sandwell, D., 2016, 南加州地震周期加载的垂直指纹特征：《自然·地球科学》，第9卷，第611-614页，doi:10.1038/ngeo2741. 2. Limber, P., Barnard, P.L. 与 Hapke, C., 2015, 21世纪加州海岸崖岸后退预测研究：收录于Wang, P., Rosati, J.D. 与 Cheng, J. 主编的《2015年海岸泥沙会议论文集》，世界科学出版社，共14页，doi:10.1142/9789814689977_0245 3. Roelvink, J.A., Reniers, A., van Dongeren, A.R., van Thiel de Vries, J., McCall, R., 与 Lescinski, J., 2009, 风暴对海滩、沙丘与障壁岛的影响模拟：《海岸工程》，第56卷，第1133–1152页，doi:10.1016/j.coastaleng.2009.08.006. 4. Tolman, H.L., Balasubramaniyan, B., Burroughs, L.D., Chalikov, D.V., Chao, Y.Y., Chen H.S., Gerald, V.M., 2002, NCEP风成海面波浪模式的开发与实施：《天气预报》，第17卷，第311-333页. 5. Vitousek, S. 与 Barnard, P.L., 2015, 预测长期海岸线变化的非线性隐式单线模型：收录于Wang, P., Rosati, J.D. 与 Cheng, J. 主编的《2015年海岸泥沙会议论文集》，世界科学出版社，共14页，doi:10.1142/9789814689977_0215.