CoSMoS (Coastal Storm Modeling System) Southern California v3.0 Phase 1 (100-year storm) sea-level rise 1.0 m: ocean currents projections

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 I data for Southern California include flood-hazard information for the coast from the border of Mexico to Pt. Conception. Changes from the initial November 2015 release may be reflected in small areas. Data are complete for the information presented but are considered preliminary; additional changes may be reflected with model improvements made for the Phase II data release in summer 2016. 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. For Phase I, only the 100-year storm is run. 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 II grids and generate initial profiles of the 4,802 CSTs used for Tier III XBeach modeling. 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: 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.预估灾害：针对指定风暴情景与海平面上升（Sea-Level Rise, SLR）情景，由模型推导得到的洋流速度（单位：米每秒）。 模型概述：海岸风暴模拟系统（Coastal Storm Modeling System, CoSMoS）可在大地理尺度（数百千米）上针对当前及未来海平面上升（SLR）情景，对风暴引发的海岸洪涝与侵蚀开展米级精度的详细预测。针对南加州的CoSMoS v3.0可针对未来气候情景（海平面上升与风暴）生成预估结果，为应急响应人员与海岸规划者提供关键的风暴灾害信息，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。 南加州第一阶段数据涵盖从墨西哥边境至康塞普申角（Pt. Conception）沿岸的洪涝灾害信息。2015年11月初始版本发布后，部分小区域可能已更新内容。所呈现的数据已完整呈现当前信息，但仍属于初步成果；2016年夏季发布的第二阶段数据将纳入模型改进后的更多更新内容。 细节说明：模型架构：CoSMoS模型包含三个层级。 第一层（Tier I）包含1个用于计算潮汐、水位变化、水流与洋流的Delft3D水动力FLOW网格，以及1个用于计算陆架区域波浪生成与传播的SWAN网格。FLOW与SWAN模型采用双向耦合模式，使波浪传播与成长过程中考虑潮流影响，同时波浪产生的轨道流速也会对潮流产生修正作用。第一层的SWAN与FLOW网格采用完全一致的结构化曲线网格，覆盖远海至近岸区域，分辨率从远海的0.5千米渐变至近岸的0.2千米。在第一层FLOW网格的所有开边界上，均施加了空间分布变化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。每个模型时间步长内，所有网格单元均会应用由CaRD10数据集（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）提供的时空变化风场（分解为东向与北向分量）与海平面气压（Sea-Level Pressure, SLP）场。针对21世纪代表性浓度路径（Representative Concentration Pathway, RCP）4.5气候情景（2011-2100年），采用WaveWatch III数值波浪模型（Tolman等，2002）与GFDL-ESM2M全球气候模型（Global Climate Model, GCM）的3小时间隔风场数据，为第一层SWAN模型的开边界提供深水波浪条件的预估数据。 第二层（Tier II）在近岸与需要更高物理过程分辨率的区域（例如海湾、港口与河口）采用更高分辨率。通过1个嵌套外网格与多个双向耦合区域分解（Domain Decomposition, DD）结构化网格，可实现局部区域的网格加密与更高分辨率设置。第二层模型沿南加州湾划分为11个分区，以降低计算量并在算力限制内完成模拟。 从第一层模拟结果中提取的水位与诺伊曼时间序列，分别应用于各第二层子模型外网格的岸线平行开边界与侧向开边界。部分子模型在侧向诺伊曼边界条件下出现不稳定，针对此类情况，将一侧或两侧侧向边界转换为水位时间序列，或保持未赋值状态。开边界时间序列均取自已完成的第一层模拟结果，因此第二层与第一层之间不存在双向数据交互。由于这种单向嵌套可能在第二层边界附近产生误差，且任何模型边界附近的数据均存在不确定性，因此第二层子模型的范围在沿岸方向上设置为相互重叠。在向陆方向，第二层区域分解网格延伸至10米等深线，仅在洛杉矶河等河道或其他低洼区域向内陆延伸较远的情况除外。与第一层模拟一致的时空变化风场与SLP场，将应用于所有第二层区域分解网格，以模拟风增水与局部逆气压效应（Inverse Barometer Effect, IBE，即水位随大气压强梯度变化而抬升或下降）。 第二层FLOW模型域中共包含42个时间序列河道流量，用于模拟高河道向海流量与向内陆迁移的沿海风暴增水峰值交汇时产生的回流加剧洪涝现象。时变河道流量要么施加于闭合边界，要么作为点源分布于相关模型域内。 波浪计算采用SWAN模型，每个第二层子模型均配置两套网格：一套覆盖范围与外FLOW网格一致的大网格，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水深约800-1000米的区域延伸至陆上8-10米高程区域，向陆延伸的设置可用于更高SLR情景下的波浪计算。沿第二层子模型外SWAN网格的开边界，每隔约1千米就会应用从已完成的第一层模拟结果中提取的时空变化二维波浪谱。与第一层模拟一致的时空变化风场，也将应用于两套第二层SWAN网格，以计算局地波浪生成过程。 第三层（Tier III）覆盖整个南加州湾，包含4802条沿岸方向间距约100米的跨岸断面（Cross-Shore Transect, CST）。断面范围从-15米等深线延伸至至少NAVD88基准面以上10米高程处。若断面向陆端存在泻湖或其他水道，则对断面进行截断处理。从与跨岸断面向海端重合的第二层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、峰值入射波向Dp），将应用于各跨岸断面的开边界。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貌动力变化过程。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模型纳入XBeach模拟，以考虑与短波入射波相比，可显著延伸波浪爬高影响范围的亚重力波（Roelvink等，2009）。美国西海岸由于长周期涌浪（Tp>15秒）的破碎作用，岸线区域对亚重力波尤为敏感。 将Delft3D模型（高关注度海湾与沼泽区域）与开放海岸XBeach模型（跨岸断面）得到的最终水位（Water Levels, WLs）进行空间合并与插值，生成10米分辨率的网格数据。将这些水位高程值与原始2米分辨率数字高程模型（Digital Elevation Model, DEM）进行差值计算，以确定最终的洪涝范围与洪涝深度。 模拟情景与事件：模型系统将针对预设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年一遇风暴情景。第一阶段仅模拟了100年一遇风暴。首先通过沿岸总水位代理（Total Water Level Proxy, TWLpx）时间序列识别风暴事件。TWLpx基于对构成总水位的主要过程进行线性叠加计算得到，覆盖21世纪大部分时段（2010-2100年）。随后对TWLpx时间序列进行极端事件筛选，以此作为后续CoSMoS模拟的边界条件。共确定多个100年一遇风暴事件（有效波高Hs、峰值周期Tp、入射波向Dp各不相同），并开展多组模型模拟，以更全面地考量区域与方向对洪涝的影响。将模型结果整合后，生成针对特定情景的洪涝预估合成数据。 数字高程模型（DEM）：本研究的无缝岸线-水深一体数字高程模型（DEM）主要基于加州海岸地形水深融合项目DEM构建，美国地质调查局地球资源观测与科学（Earth Resources Observation and Science, 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。地形数据源自2009-2011年加州海岸保护局激光雷达（Light Detection and Ranging, lidar）项目采集的裸土激光雷达数据，水深数据则源自2009-2010年的机载激光测深数据，以及2001-2013年采集的声学多波束与单波束测深数据。本DEM尽可能精准地刻画近岸、海滩与崖面的形态，整合了数十套水深与地形数据集。这些数据主要用于填充第二层网格，并为第三层XBeach建模所用的4802条跨岸断面生成初始剖面。所有数据均采用NAD83水平基准面与NAVD88垂直基准面。第二层与第三层数据采用UTM投影，分带11。 输出内容包括：100年一遇风暴与0.0米海平面上升情景下的预估洋流速度。数据覆盖近岸区域，包括在同一风暴与海平面上升模拟中，受风暴潮、海平面异常、潮汐水位与波浪爬高影响的沿海洪涝脆弱区域。 参考文献： 1. 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. 1133–1152, doi:10.1016/j.coastaleng.2009.08.006. 2. 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.