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Measurements of Waves in a Wind-wave Tank Under Steady and Time-varying Wind Forcing
Published on: February 13, 2018
Uncertainties in extreme surge level estimates from observational records
H W van den Brink1, G P Können, J D Opsteegh
1Royal Netherlands Meteorological Institute, PO Box 201, 3730 AE De Bilt, The Netherlands.
Summary
Climate simulations reveal that the Generalized Extreme Value (GEV) distribution is the most reliable method for estimating extreme surge levels. This approach accounts for uncertainties in climate models and sample data, crucial for accurate flood risk assessment.
Area of Science:
- Climate Science
- Oceanography
- Extreme Value Theory
Background:
- Accurate estimation of extreme sea surge levels is critical for coastal flood risk assessment in regions like Delfzijl, The Netherlands.
- Existing methods for analyzing surge data face challenges related to model and sample uncertainty.
Purpose of the Study:
- To evaluate the reliability of the Generalized Extreme Value (GEV) and Generalized Pareto Distribution (GPD) for estimating extreme surge levels.
- To assess model and sample uncertainties in surge level predictions for return periods like 104 years.
Main Methods:
- Ensemble climate simulations (7540 years) coupled with a surge model to generate North Sea wind fields and skew surge levels.
- Analysis of 65 constructed surge records (116 years each) using GEV and GPD statistical distributions.
- Investigating the optimal threshold selection for GPD and the sensitivity of estimates to this choice.
Main Results:
- The GEV distribution applied to storm-season maxima is identified as the most robust approach due to objective threshold determination challenges with GPD.
- GPD estimates can be overly sensitive to threshold choice and tend towards underestimation.
- If GPD is used, the exceedance rate (lambda) should not exceed 4.
- Climate model suggests a potential second population of intense storms, implying 104-year wind-speed estimates from 100-year records are lower limits.
Conclusions:
- The GEV distribution is recommended for analyzing storm-season maxima to estimate extreme surge levels, offering more reliable results than GPD in this context.
- Acknowledging potential intense storm populations is vital for interpreting extreme wind-speed estimates from limited data.
- Careful consideration of statistical methods and data limitations is essential for accurate coastal flood risk management.
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