The Development of Inundated Storm Surge Operational System for Taiwan Regions

The First Taiwan West Pacific Global Forecast System Development Workshop 第一屆臺灣與西北太平洋全球預報系統發展研討會 The Development of Inundated Storm Surge Operational System for Taiwan Regions

Yu-Lin Tsai1, Tso-Ren Wu1, Chuen-Teyr Terng2, Chi-Hao Chu2 蔡育霖1, 吳祚任1, 滕春慈2, 朱啟豪2 1Graduate Institute of Hydrological and Oceanic Sciences, National Central University 2Marine Meteorology Center, Central Weather Bureau

Tsunami Science Laboratory Background • Storm surge is a abnormal sea water rise commonly associated with low pressure weather systems (such as tropical cyclones, storms, typhoons, and hurricanes).

• The two main meteorological factors contributing to a storm surge are a long fetch of winds spiraling inward toward the storm, and a low-pressure-induced dome of water drawn up under and trailing the storm's center.

Taiwan

Sea Surface induced by typhoons (Wiki)

Philippines

Storm Surges with Tidal Effect (Wiki) Potential Disaster induced by Storm Surges • Destroy of homes and business • Potential threat of coastal communities • Damages of roads and bridges

Inundation induced by 2005 Hurricane Katrina. (http://www.stormsurge.noaa.gov/)

Flooded by storm surge of Hurricane Katrina (2005) in the northwest New Orleans. Our Goals for a Storm Surge Operational System

• Spherical coordinate system with a large computational domain should be adopted to cover the complete life cycle of the typhoon .

• Nonlinear, bottom shear stress and shoaling effects should be all considered in nearshore and multi-scale wave propagation.

Copyright @ Taiwan Typhoon and Flood Research Institute • High-resolution inundation calculation. Uncertainty of Storm Tracks

• Couple with the dynamic atmospheric model.

• Couple with the global tidal model.

• High-speed efficiency for the early-warning system.

Multi-Scale Storm Surge Propagation (NOAA) The Introduction of Storm Surge Model (COrnell Multi-grid COupled of Tsunami Model – Storm Surge)

Nonlinear Shallow Water Equations on the Spherical Coordinate  1  P   cos Q  0 tRcos    

2 s P11  P  PQ gH  b H Pa F    fQ  F    t Rcos   H R   H R cos    ww R cos    

2 s Q11  PQ  Q gH  b H Pa F    fP  F    t Rcos   H R   H R   ww R   

• Solve shallow water equations on both spherical and Cartesian coordinates • Explicit leapfrog Finite Difference Method for stable and high speed calculation • Multi/Nested-grid system for multiple shallow water wave scales • Moving Boundary Scheme for inundation • High-speed efficiency (1). Validation of Inundation Calculation Compare with the solitary wave run-up experiments (Synolakis, 1986 and 1987).

(from NOAA Official Website)

soliton

Simulated by COMCOT (Wu, 2012) (2). Validation of Pressure Gradient

2 P11  P  PQ gH  b H Pa    fQ  F   t Rcos   H R   H R cos    w R cos   

P gH H P    a t Rcos   w R cos   

Steady-State Analytic Solution

2  1  2 Pa  9800  sin  1013.25  10 21

Pa 2  1      sin  gw  21  The simulated water elevation generated by the pressure gradient is in a good agreement with steady-state analytic solution. (3). Validation of Wind Shear Stress

2 s P11  P  PQ gH  b F    fQ  F  t Rcos   H R   H R cos    w P gH  F s  tRcos  w

Steady-State Analytic Solution

The simulated water elevation generated by the wind shear stress is in a good agreement with steady-state analytic solution. (4). High-speed Calculation Our model can finish 48 hrs forecast in 3 hours and be used for the operational system.

Parallel Computing on Multi Cores.

Dynamic resources sharing.

The results has been published on Ocean Engineering (Lin et al., 2015). (5). Couple with the Atmospheric Model TWRF (Typhoon Weather Research and Forecasting Model)

Wind Field • TWRF model is an atmospheric model adopted for operational forecasts by Central Weather Bureau in Taiwan.

• The TWRF model will start its simulation per 6 hours in a day at 00, 06, 12 and 18 UTC time respectively.

Pressure Field

Computational Domain (CWB) (6). Couple with Global Tide TPXO Model (OSU TOPEX/POSEIDON Global Tidal Model)

The tides are provided as complex amplitudes of earth-relative sea-surface elevation for eight primary (M2, S2, N2, K2, K1, O1, P1, Q1), two long period (Mf,Mm) and 3 non-linear (M4, MS4, MN4) harmonic constituents.

User Interface of TPXO

TPXO can provide tidal information, like M2. (Dushaw et al., 1997) (7). High-Accuracy Tide Calibration The bias is smaller than 0.1 m and root mean square is smaller than 0.6 m.

Validated Gauge Locations at Taiwan The observed data and harmonic data are provided by CWB (Taiwan). 8. Model Validation - 2010 Typhoon Megi • Severe Typhoon Megi was the strongest typhoon in 2010 and generated the destructive storm surges at Philippines. After Megi passed through Philippines, it turned northward to China and the Taiwan Strait. The typhoon route of Megi was defined as track type 9 by CWB.

The results are storm surge, pressure field and wind field. Gauge Comparison 2010.10.15 00:00 – 2010.10.23 12:00 (UTC+0) Inundation Area and Maximum Surge Height Storm Tides Tides

The simulated results on the resolution of 200 meters indicated that Jiangjyun, Anping and Kaohsiung would be potentially surge-flooded areas. Storm Surge Operational Process

COMCOT Start INPUT Storm Surge OUTPUT Exit Model

Parametric Typhoon Model (3 hr/cycle) / TWRF Model (6 hr/cycle)

 Meteorological Force: Parametric Typhoon Model or TWRF Model. INPUT  Tidal Boundary Condition: TPXO 7.1 model.

 48-HR Time Series for Storm Tide and Pure Tide at 34 specified locations. OUTPUT  2-dimensional model product. Schematic Diagram for Storm Tide Run and Pure Tide Run

48-HR Warm-up 48-HR Forecast Storm Tide Run Start (Storm Surge + Tide) 2015.09.01 2015.09.03 2015.09.05 02:00 (UTC+8) 02:00 (UTC+8) 02:00 (UTC+8)

Pure Tide Run 96-HR Forecast 2015.09.01 2015.09.05 02:00 (UTC+8) 02:00 (UTC+8)

1. Every forecasting includes two 96-HR computations, and one for storm tide (storm surge + tide) run and another for pure tide run.

2. There are 48-HR warm-up and 48-HR forecast at each storm tide run. Nested Domains for Taiwan Regions

LAYER 01 LAYER 02 Resolution: 8 km

Resolution A, B, C, and D: 2 km E, F, and G: 1 km H: 0.5 km

• Layer 01 can cover the complete typhoon life cycle and the full storm surge propagation. • Layer 02 can include the offshore hydrodynamic progresses of storm surge on the fine mesh domains and couple with tidal effect. Grid Information of Computational Domain

X-Dir Y-Dir Total Resolution

LAYER 01 361 376 135,736 4 arc-min (~ 8 km) LAYER 02-A 120 84 10,080 1 arc-min (~ 2 km) LAYER 02-B 44 132 5,808 1 arc-min (~ 2 km) LAYER 02-C 76 68 5,168 1 arc-min (~ 2 km) LAYER 02-D 52 112 5,824 1 arc-min (~ 2 km) LAYER 02-E 72 40 2,880 0.5 arc-min (~ 1 km) LAYER 02-F 80 80 6,400 0.5 arc-min (~ 1 km) LAYER 02-G 136 112 15,232 0.5 arc-min (~ 1 km) LAYER 02-H 80 32 2,560 0.25 arc-min (~ 0.5 km)

Total Grid Number: 189,688 (about 200 thousands) grids. Model Product – Forecast Water Elevation Series 48-HR forecasting time series of storm tide and pure tide at 34 specified locations.

34 Specified Locations Combine with CWB display system Model Product - Surge Inundated Warns

The Greens indicate that these regions are safe areas and without the potential surge- inundated warns.

The Oranges indicate that these regions are under the potential threat of surge inundation.

• The surge-inundated warns will be determined automatically by the dry- wet-cell treatment.

• If potentially-inundated areas are calculated, the signs will change the colors from green to orange. Model Product – 12-HR Maximum Strom Surge

2015 Typhoon Soudelor is chosen as demo. Model Product – 12-HR Residual (Max Storm Tide – Max Tide)

2015 Typhoon Soudelor is chosen as demo. Maximum Storm Tide along Shoreline

Storm Tide = Storm Surge + Tide

BLUE ：0.0 <= zmax < 0.5 m CYAN ：0.5 <= zmax < 1.0 m GREEN ：1.0 <= zmax < 1.5 m YELLOW：1.5 <= zmax < 2.0 m RED ：2.0 <= zmax m Combine with GIS Software Conclusion • Our COMCOT storm surge operational system : • Solve nonlinear shallow water equations with multi-scale wave propagation. • Adopt large computational domain to cover the complete typhoon life cycle and full storm surge propagation. • Couple with dynamic atmospheric TWRF model and global TPXO tidal model. • Validate with solitary wave run-up experiment and meteorological idealize cases. • Accurate tide calibration.

• Provide model products: • 48-HR time series of storm tide and pure tide at 34 specified locations. • 12-HR maximum storm surge and residual. • Maximum storm tide along shoreline. Thank You! • Combine with GIS. Yu-Lin Tsai: [email protected]