IMPACT OF GLOBAL CLIMATE CHANGE ON WAVE CLIMATE Nobuhito Mori 1 , Ryota Iwashima 2 Tomohiro Yasuda 1 , Hajime Mase 1 , Tracey Tom 2, 3 and Yuichiro Oku 1 Abstract The influence of global climate change due to green house effects on the earth environment will be required impact assessment, mitigation and adaptation strategies for future our society. This study predicts future ocean wave climate in comparison with present wave climate based on the atmospheric general circulation model and global wave model. The annual averaged and extreme sea surface winds and waves are analyzed in detail. There are clear regional dependence of annual average and extreme value from present to future climate. The wind speeds and wave heights of future climate are increased in middle latitudes and the Antarctic ocean, and these are decreased in the equator. The annual averaged winds and waves are decreased off coast of Japan but their maxima are increased than those of present climate. Key words: global warming, climate change, sea surface wind, ocean wave 1. Introduction The influence of global climate change due to green house effects on the earth environment will be required impact assessment, mitigation and adaptation strategies for future our society. The sea-level rise has been observed at a rate of 1.7 mm ± 0.3 mm/yr from 1870 to 2004 and a significant acceleration of sea-level rise during the last ten years is observed (Church and White, 2006). However, the sea-level rise is a static side issue of climate change and is important for human activity near the coastal zone (IPCC, 2007). The major source of the sea-level rise is thermal expansion of sea water temperature increase. On the other hand, ocean waves and storm surges are dynamic side issue of climate change. These dynamic phenomena will be necessary to be taken into the consideration for coastal disaster prevention and reduction, if extreme weather events will become stronger than those in the present climate. For example, the north Atlantic observed wave data shows 5 cm/yr increase of annual maxima for the last 40 years (Wang and Swail, 2002). The wave hindcasts in the Atlantic ocean show more significant wave height increase in the region off the Canadian coast and the northwest of Ireland but less significant change in the North Sea and in the region off the Scandinavian coast (Wang and Swail, 2002). The long-term change of storm waves and surges are important for infrastructures at coastal zone. For example, a coastal breakwater design is basically determined by wave pressure of maximum wave condition, a design wave, for durable period and the wave pressure is proportional to the wave height. Moreover, an equilibrium condition of coastal beach profile depends on seasonal or annual wave height, period and direction. Therefore, the dynamic changes of ocean surface by the climate change will give significant impacts to extreme and daily coastal environments. These effects will be at greatest risk at coastal areas, especially heavily populated mega delta region in East, South-East and South Asia, due to wave climate change. The total land area of Japan is approximately 378,000 square kilometers; coastal areas of Japan where are 20 1 Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan, Tel.: +81-774-38-4146, Fax.: +81-774-38-4321, email: mori@oceanwave.jp. 2 Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto, Japan. 3 Surflegend Co. Ltd., 3-1-1 Tsujido Nishikaigan, Fujisawa, Kanagawa 251-0046, Japan, Tel.: +81-466-35-7955, Fax.: +81-466-35-7953, email: tracey@surflegend.co.jp. Coastal Dynamics 2009 Paper No. 135 1