A System for Estimating Wave Climate and Wave Extremes Based on 20-Year Wave Hindcast and Its Verification at the Measurement Stations around Japanese Coasts

Abstract

A long-term wave hindcast system which consists of the ECMWF wind data sets over a period of 20 years from 1979 to 1998 and a shallow water wave model based on backward ray tracing is applied to the estimation of year-long waves at each of almost all measurement stations deployed around the coasts of Japan. Comparison between 2-3 hourly measurement and hindcast is made for a time series of waves, wave climate parameters of each month or over the whole period, their climatic change and extreme wave height. One main finding is that the system is very useful not only for a proper evaluation of the wave climate and its interannual change but also for a first guess of the return wave height with confidence interval at any coastal location around Japan directly facing the open sea, particularly on the Japan Sea coasts. INTRODUCTION Proper and efficient estimation of long-term wave climate and wave extremes at any location in the coastal sea areas is an indispensable step for the analysis of the coastal process related to wave-induced sediment transport and the design of coastal defense facilities. Hatada et al. (2000) have established a long-term wave hindcast system for estimating wave climate over more than several years around the coasts of Japan, in which the analysis surface wind data sets provided by ECMWF (European Centre for Medium-range Weather Forecasts) are used. But a hindcast period of 8 to 13 years is too short to properly evaluate climatic change of wave conditions and wave extremes. Now the ECMWF analysis and reanalysis surface wind data sets over more than 20 years since 1979 have been released to the public domain. 1 Research Assistant, Department of Civil and Environmental Engineering, Faculty of Engineering, Ehime University, Bunkyocho 3, Matsuyama 790-8577, Ehime Prefecture, Japan, hatada@en2.ehimeu.ac.jp 2 Professor, Department of Civil and Environmental Engineering, Faculty of Engineering, Ehime University, Bunkyocho 3, Matsuyama 790-8577, Ehime Prefecture, Japan, myamag@en2.ehime-u.ac.jp