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Projection of Future Wave Climate for Coastal Environment Prediction

Introduction

Research of global climate change due to greenhouse effects on the earth's environment is changing from understanding phenomena to impact assessment, mitigation and adaptation strategies for future development of human society. Sea-level rise has been observed at a rate of 1.7 mm plus minus 0.3 mm/yr from 1870 to 2004 and a significant acceleration of sea-level rise was observed in the last ten years (Church and White, 2006). The major source of the sea-level rise is thermal expansion of sea water temperature increase, thus the sea-level rise is a static side issue of climate change influence. Sea-level rise greatly impacts human activity near the coastal zone (IPCC, 2007) and simply exacerbates the vulnerability of coastal regions to other physical processes (e.g. storm surges, storm waves). Another direct influence of sea-level rise is the inundating of low level coastal areas which is of concern.

On the other hand, ocean waves and storm surges of future climate are also expected to change characteristics from the present climate and are the dynamic side issue of climate change. It is necessary to seriously consider the impacts of these dynamic phenomena 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). In addition, long-term changes of storm waves and surges are important for infrastructures near the coastal zone. For example, a coastal breakwater design is basically determined by the wave pressure of the maximum wave condition, the so-called design wave, for durable period and the wave pressure is proportional to the wave height. Moreover, coastal erosion is another critical issue, where more than 70% of sandy beaches around the world are presently erosional. Equilibrium condition of coastal beach profile depends on seasonal or annual wave height, period and direction. The projection of future change on coastal erosion is insufficient due to information deficiencies on changes in waves and coastal currents. Therefore, future ocean wave climate change will have significant impacts on extreme and daily coastal environments. These influences will be at greatest risk at coastal areas, especially in the heavily populated mega delta regions of East, South-East and South Asia. The future coastal environmental changes give a big influence to these regions, directly.

The future wave climate projection has been conducted by a few researchers (e.g. Hemer et al., 2006). These studies have shown an increase in wave height due to increased wind speeds associated with mid-latitude storms in many regions of the mid-latitude oceans. Zhang et al. (2004) and Wang and Swail (2006) made statistical projections of global wave height from the empirical relationships between sea level pressure and significant wave height. Furthermore, the dynamical regional wave climate projections has been carried out in Europe and North America but there is no dynamical global wave climate projection at present.

This study projects future wave climate and analyzes differences between present and future ocean wave climate models. The averaged and extreme ocean wave climate changes on both global and regional scales are discussed.

This project is coupled with Projection of Tropical Cyclone and Storm Surge and is a part of Innovative Program of Climate Change Projection for the 21st Century which is supported by Japanese government.

Collaborators

  • Hajime Mase, DPRI
  • Tomohiro Yasuda, DPRI
  • Sota Nakajo, Kumamoto University
  • Tomya Shimura, DPRI

Outline

Direct projection of sea surface wind and wave climate change

This research uses the product of global climate projections on the basis of 20 km high-resolution GCM developed by Meteorological Research Institute (MRI)/ Japan Meteorological Agency (JMA) AGCM model (denoted by GCM for simplicity hereafter). The 20 km high-resolution MRI-JMA GCM is the single atmospheric GCM with T959L60 resolution following A1B scenario and is newly developed for the Kakushin (2007) program (Kitoh et al., 2009).

The global wave climate projections for the three periods were simulated by the SWAN (Simulating WAves Nearshore) model (Booij et al., 1999) using sea surface wind at 10 m height U10 of the GCM. The long-term wave climate changes were analyzed both for the global scale and regional oceans. The analysis of computed future wave climate change from the present climate are conducted in detail.

wgcm_difference_nor.jpg

Ratio of averaged wave height change from the present (1978-2004) to future (2075-2099) climate conditions. The positive means increased wave height from the present climate.

wgcm_regionalchange.jpg

Regional changes of averaged and extreme wave height from the present to future climate conditions (NA:The North Atlantic, NP:The North Pacific, JP:Around Japan).

Data Archive

Following netcdf data set are one of our results based on this project. These data set are basically free for academic purpose but please refer to following references when you use the data set. If you want to know in detail please ask me directly.

Data source

The data is NetCDF formatted and the mean and extreme values are included.

The wave data has been updated in 2012/08/22. It improved data quality around the Florida. Please use the latest data for research purpose.

Joint Research

  • Coordinated Ocean Wave Climate Projections

References

Journal paper published

  1. Mori, N., T. Yasuda, H. Mase, T. Tom and Y. Oku (2010) Projection of extreme wave climate change under the global warming, Hydrological Research Letters, Vol.4, pp.15-19. (doi:10.3178/hrl.4.15)

Conference proceedings

  1. Mori, N., T. Yasuda, R. Iwashima, T. H. Tom, H. Mase and Y. Oku (2009) Impact of global climate change on wave climate, Coastal Dynamics 2009, CD-ROM, No.135.
  2. Mori, N., T. Yasuda, H. Mase, R. Iwashima (2009) T. H. Tom and Y.Oku, Prediction of global sea surface wind and wave climate change based on MRI-JMA GCM, Proceedings of 33rd IAHR Congress, No.10980, 8p.