Comprehensive Review of Integrated Coastal Protection Planning and Policy Support for Coastal Protection Plans
Rolling Review of Protection Zone Delineation
The Level 1 and Level 2 Coastal Protection Plans were successively announced and implemented by the Ministry of the Interior in 2020 and 2021. Subsequently, in coordination with the Ministry of the Interior’s overarching plan, the “First Comprehensive Review of the Integrated Coastal Zone Management Plan” (announced and implemented in 2025), this Branch formally incorporated the issue of “Adaptation Strategies in Response to Climate Change Scenarios” into the Reference Manual for Integrated Coastal Protection Planning and revised the relevant principles for delineating storm-surge inundation potential areas.
In the future, when agencies responsible for preparing coastal protection plans review coastal protection facilities, in addition to reviewing the current functions of the protection facilities, they shall also systematically examine potentially vulnerable sections of seawalls that may be affected by projected changes in oceanographic conditions under climate change scenarios (Table 1). Based on the results, the potential extent of storm-surge inundation under climate change scenarios (Figure 1) shall be incorporated into the landward buffer zone of the protection plan, and prohibited and compatible land-use management provisions within the protection zone shall be established to ensure proper land-use management within the area.
Application of Climate Change Projections for Oceanographic Conditions
To ensure consistency in the sources of relevant scientific data, it is recommended that climate change-related data for coastal protectiFigure 1. Distribution of Storm-Surge Inundation Depth for a 50-Year Return Period under a Climate Change Scenario (Yunlin as an Example; Not an Actual Officially Announced Result) Application of Climate Change Projections for Oceon primarily draw on the value-added application data from the National Science and Technology Council’s TCCIP “Taiwan Climate Change Projection Information and Adaptation Knowledge Platform Project.”
However, because tidal levels exhibit considerable spatial variability and the data available on the platform are not readily applicable directly to coastal protection plans, this Branch obtained customized data through a cooperative agreement platform according to specific needs—namely, increments at specific locations for a 50-year return period. These data were then used to review changes in coastal protection water levels throughout Taiwan (Figure 2) and to calculate the rates of change in storm-surge anomalies under climate change (Figure 3), providing a reference for future “Comprehensive Reviews of Integrated Coastal Protection Planning.”
Comprehensive Review of Coastal Protection Water Levels and Study of Climate Change Impacts
The design conditions for tides, waves, and other factors for Taiwan’s general seawalls have undergone unified reviews through projects including the “Taiwan Provincial Seawall Improvement Plan” in 1976, the “Review Plan for Seawall Design Elevations throughout Taiwan” in 1992, and the “Review of Tidal Protection Functions of General Seawalls” in 2014.
Since 2014, however, no comprehensive review of protection standards for Taiwan proper and its offshore islands has been conducted. With the continuous expansion of oceanographic and hydrological observation data in recent years, it is necessary to re-examine the original protection standards.
Furthermore, climate change-related issues have been incorporated as important topics in the “Comprehensive Review of Coastal Protection Plans” and “Integrated Watershed Improvement and Adaptation Planning.” This study comprehensively reviews typhoon storm-surge protection water levels and deep-water wave heights for various return periods throughout Taiwan, including offshore islands, to provide references for River Management Branches and local governments in conducting comprehensive reviews of coastal protection plans.
Collection and Analysis of Oceanographic and Hydrological Data
For the coasts of Taiwan proper and the offshore islands of Penghu, Kinmen, Matsu, Green Island, and Orchid Island, long-term oceanographic and hydrological data within the project area are collected, compiled, statistically analyzed, tabulated, and plotted for subsequent selection as model input conditions and for model validation.
Harmonic Analysis and Statistical Analysis of Astronomical Tides
For each coastal sector of Taiwan proper and the offshore islands, time-series data from tide-gauge stations are collected and analyzed to determine the mean high water level at spring tide and long-term statistical averages as defined in the “Design Guidelines for Coastal Protection Facilities – Seawalls.”
In addition, time-series data from each station are analyzed using harmonic analysis to resolve tidal constituents. The results can be used to predict future changes in astronomical tidal levels or to supplement tidal data for individual regions. When future protection plans or related analyses are conducted in areas where measured tidal-level data are unavailable, combinations of tidal constituents for each coastal sector can be used to reconstruct and fit astronomical tidal-level variations at individual stations.
Development and Validation of Hydrodynamic and Wave-Spectrum Numerical Models
Since the previous project, most monitoring stations have accumulated an additional 10 years of records. At present, approximately 90% of tide-gauge stations in the various coastal sectors have records exceeding 20 years.
Based on historically observed maximum high-water levels during typhoon events, typhoon storm-surge protection water levels for 5-, 10-, 20-, 25-, 50-, and 100-year return periods are estimated. These results can serve as references for future coastal protection plans and for establishing protection design criteria for general seawall sections, as shown in Figure 4.
Assessment of Storm-Surge Impact Duration
Historical typhoon events for which the Central Weather Administration issued typhoon warnings are used as the selection criteria. The maximum storm-surge anomaly and its time-series distribution for each typhoon event in each region are extracted to conduct return-period analysis of storm-surge anomalies.
Based on the simulated storm-surge anomaly water level reaching a “specified water-level elevation,” the time interval for significant storm-surge impact duration is calculated. A comprehensive assessment is then conducted of the total duration from the beginning to the end of storm-surge anomalies induced by meteorological effects that exceed a specified threshold.
By compiling and comparing the average significant storm-surge durations for Taiwan’s coastal sectors under different screening criteria, it is recommended that a storm-surge anomaly water level reaching the 5-year return-period storm-surge anomaly elevation be adopted as the screening criterion for calculating the time interval of significant storm-surge impact duration, as shown in Table 2.
Assessment of Storm-Surge Impact Duration
By collecting and reviewing the latest literature related to global climate models for climate change and adopting the downscaled climate change scenario projections from the Taiwan Climate Change Projection Information and Adaptation Knowledge Platform, estimates of climate change-induced storm-surge anomalies and deep-water wave heights are developed.
The results can serve as references for future applications, including the formulation of coastal protection plans and coastal protection management strategies.