CoSMoS (Coastal Storm Modeling System) Southern California v3.0 Phase 1 (100-year storm) sea-level rise 0.0 m: wave-hazard projections

Projected Hazard: Model-derived significant wave height (in meters) 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 wave height 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：基于模型推导的、对应给定风暴工况与海平面上升（sea-level rise, SLR）情景的有效波高（单位：米）。
模型概述：沿海风暴模拟系统（Coastal Storm Modeling System, CoSMoS）可在数百公里级的地理范围内，针对当前及未来海平面上升（sea-level rise, SLR）情景，对风暴引发的海岸洪涝与侵蚀开展米级分辨率的精细化预测。用于南加州的CoSMoS v3.0可针对未来气候情景（含海平面上升与风暴过程）开展预估，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了从墨西哥边境至康塞普西翁角（Pt. Conception）沿岸的洪涝灾害信息。2015年11月初始版本发布后的变更可能仅体现在小范围区域内。本次呈现的数据内容完整，但仍属于预发布版本；2016年夏季第二阶段数据发布时，将结合模型优化更新进一步补充调整。
详细说明：
模型背景：CoSMoS模型分为三个层级。第一层级包含1个用于计算潮汐、水位变化、流场与环流的德尔夫特3D流体动力学FLOW网格（Delft3D hydrodynamics FLOW grid），以及1个用于计算陆架区波浪生成与传播的SWAN网格（SWAN grid）。FLOW与SWAN模型采用双向耦合方式，使潮汐环流参与波浪传播与成长过程，同时波浪产生的轨道流速也会反向影响潮汐环流。第一层级的SWAN与FLOW模型采用一致的结构化曲线网格，网格范围从远海延伸至近岸，分辨率从远海的0.5千米逐步提升至近岸的0.2千米。沿第一层级FLOW网格的所有开边界，均加载了空间变化的天文潮汐振幅与相位，以及由大尺度效应（如长期海平面上升）引发的水位比容增量。在每个模型时间步长内，向所有网格单元加载由CaRD10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（数据来源：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年书面通信）。针对21世纪典型浓度路径（Representative Concentration Pathway, RCP）4.5气候情景（2011-2100年），利用WaveWatch III数值波浪模型（Tolman等，2002）与来自GFDL-ESM2M全球气候模型（Global Climate Model, GCM）的3小时间隔风场，对第一层级SWAN模型开边界处的深水波浪条件进行预估并加载。
第二层级在近岸及需要更高分辨率物理过程模拟的区域（如海湾、港口与河口）提供更精细的网格分辨率。采用1个嵌套外网格与多个双向耦合的区域分解（domain decomposition, DD）结构化网格，可在需要的区域实现局地网格加密与更高分辨率。为缩短计算时长并在计算资源限制内完成模拟，第二层级沿南加州湾划分为11个计算区段。
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岸线平行边界与侧向开边界。部分子模型在侧向诺依曼边界条件下存在不稳定性，针对此类情况，将单侧或双侧侧向边界转换为水位时间序列，或保留为未加载状态。所有开边界时间序列均来自已完成的第一层级模拟结果，因此第二层级与第一层级之间无双向数据交互。由于单向嵌套可能在第二层级边界附近产生误差，且任何模型边界处的数据均存在不确定性，因此第二层级子模型范围沿海岸方向设计为相互重叠。在向陆方向，第二层级DD网格延伸至海拔10米的地形等高线，仅在洛杉矶河等河道或其他低洼向陆延伸区域存在例外。向所有第二层级DD网格加载与第一层级一致的时空变化风场与SLP场，以模拟风增水与局地反气压效应（inverse barometer effects, IBE，即水位随气压梯度变化而升降的现象）。
第二层级FLOW流域共包含42组河道径流时间序列，用于模拟因河道向海径流与向陆传播的沿岸风暴增水交汇产生的回流引发的加剧洪涝。时变河道径流可加载至闭合边界，或作为点源分布于相关模型流域内。
每个第二层级子模型均采用SWAN模型开展波浪计算，包含2个网格：1个覆盖外FLOW网格范围的大尺寸网格，以及1个分辨率更高的双向耦合近岸嵌套网格。近岸网格范围从水深800-1000米的水域延伸至陆上海拔8-10米的区域，向陆延伸范围可适配更高SLR情景下的波浪计算。沿第二层级子模型外SWAN网格开边界，每隔约1千米加载一组从第一层级模拟结果提取的时空变化二维波浪谱，同时加载与第一层级一致的风场用于局地波浪生成计算。
第三层级覆盖整个南加州湾，包含4802条跨岸断面（cross-shore transects, CST），沿岸间距约100米。断面从-15米等深线延伸至至少比NAVD88垂直基准面高10米的区域，若潟湖或其他水道存在于向陆端则进行截断处理。从与断面向海端重合的第二层级网格单元提取时变水位与波浪参数（有效波高significant wave heights, Hs；峰值周期peak periods, Tp；入射波峰值方向peak incident wave directions, Dp），加载至每条跨岸断面的开边界。采用静水压力模式（无垂直压强梯度）运行XBeach模型，包含基于单次事件的地形动力变化过程，计算波浪传播、双向波流相互作用、水位变化与波浪爬高。
CoSMoS模型加入XBeach模拟，用于考虑亚重力波对波浪爬高范围的显著扩展效应（相较于短周期入射波，Roelvink等，2009）。美国西海岸因长周期涌浪（Tp>15秒）破碎作用，近岸对亚重力波尤为敏感。
德尔夫特3D模型（针对重点海湾与沼泽区域）与开放海岸XBeach模型得到的最终水位数据，经空间合并后插值至10米分辨率网格。通过将该水位高程与原始2米分辨率数字高程模型（digital elevation model, DEM）作差，可确定最终洪涝淹没范围与淹没深度。
模拟事件：本模型系统针对预设关注情景开展模拟，如结合SLR情景的1年一遇与100年一遇风暴事件。第一阶段仅开展100年一遇风暴模拟。首先从近岸总水位代理指标（total water level proxies, TWLpx）时间序列中识别风暴事件。假设总水位由各主要过程线性叠加，据此计算2010-2100年多数时段的TWLpx时间序列。随后筛选极端事件作为CoSMoS后续模拟的边界条件，共确定多组100年一遇风暴事件（有效波高、峰值周期与入射波方向各异），开展多组模拟以全面考虑区域与方向对洪涝的影响，最终整合为情景专属的洪涝预估综合结果。
数字高程模型（DEM）：本无缝地形水深联合DEM主要基于加州沿海地形水深融合项目DEM制作，经美国地质调查局地球资源观测与科学（EROS）中心优化，整合了最新高分辨率地形与水深数据集。地形数据来自2009-2011年加州海岸保护局裸地激光雷达（light detection and ranging, lidar）数据，水深数据来自2009-2010年水深激光雷达与2001-2013年多/单波束声学测深数据。本DEM通过整合数十组数据集，尽可能精准刻画近岸、海滩与崖岸地表形态，用于填充多数第二层级网格与生成第三层级初始地形剖面。所有数据采用NAD83水平基准面与NAVD88垂直基准面，第二、三层级数据采用UTM投影第11带坐标系。
输出内容包括：100年一遇风暴与0.0米SLR情景下的预估波高，数据覆盖近岸区域，包含该风暴与SLR模拟中因风暴增水、海平面异常、潮汐高程与波浪爬高引发海岸洪涝的脆弱区域。
参考文献：
Roelvink, J.A., Reniers, A., van Dongeren, A.R., van Thiel de Vries, J., McCall, R., 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.
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.