The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology The wind-wave climate of the Pacific Ocean. Mark Hemer, Jack Katzfey and Claire Hotan Final Report 30 September 2011 Report for the Pacific Adaptation Strategy Assistance Program Department of Climate Change and Energy Efficiency [Insert ISBN or ISSN and Cataloguing-in-Publication (CIP) information here if required] Enquiries should be addressed to: Mark Hemer Email. [email protected] Distribution list DCCEE 1 Copyright and Disclaimer © 2011 CSIRO To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO. Important Disclaimer CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it. Contents Executive summary .................................................................................................... 3 1. Introduction ..................................................................................................... 11 2. Existing Knowledge ........................................................................................ 16 3. Available Data .................................................................................................. 20 3.1 United States Army Corps of Engineers (USACE) Wave Information Study (WIS) 20 3.2 ECMWF ERA-40 ..................................................................................................... 20 3.3 ERA-Interim ............................................................................................................ 21 3.4 Satellite Altimeter record (Swinburne University) .................................................... 22 3.5 In-situ Buoy Data .................................................................................................... 22 4. Data Processing Methods .............................................................................. 24 5. Assessment of the present Wave Climate..................................................... 25 5.1.1 Significant Wave Height ..................................................................................... 25 5.1.2 Directional wave climate ..................................................................................... 32 5.1.3 Site records ......................................................................................................... 43 6. Preliminary wave climate projections for the pacific region ....................... 51 6.1 An assessment of the PCCSP CCAM surface winds ............................................. 52 6.1.1 Evaluation of Currrent Climate CCAM 60 km simulations .................................. 52 6.1.2 Evaluation of the Climate Change signal in the CCAM 60 km simulation........... 58 6.2 Unadjusted CCAM forced wave models ................................................................. 61 6.2.1 Site Records ....................................................................................................... 65 6.3 Bias-Adjusted CCAM forced wave models ............................................................. 67 6.3.1 Site records ......................................................................................................... 70 6.4 Preliminary evaluation of the Climate Change signal in the Pacific wave climate .. 73 6.4.1 Un-adjusted CCAM forced runs .......................................................................... 73 6.4.2 Bias-adjusted CCAM forced runs........................................................................ 76 7. Recommendations .......................................................................................... 84 References ................................................................................................................ 86 Acknowledgements .................................................................................................. 90 Appendix A – Verification of ERA-Interim wave field ............................................ 92 A.1 Assessment of ERA-Interim against buoy data .......................................................... 92 A.2 Assessment of ERA-Interim against altimeter record ................................................. 97 Appendix B – WAVE roses from CCAM forced Wave model, for representative sites ................................................................................................................ 103 Un-adjusted CCAM forced runs (1979-2009). ................................................................ 103 Bias-adjusted CCAM forced runs (1979-2009). .............................................................. 106 i Un-adjusted CCAM forced runs (2070-2099). ................................................................. 108 Bias-adjusted CCAM forced runs (2070-2099). .............................................................. 111 EXECUTIVE SUMMARY EXECUTIVE SUMMARY Surface wind-waves are a key driver of coastal zone processes in the Pacific Island Countries and Territories (PICTs), and their climatological variability must be considered within any comprehensive assessment of potential climate change driven impacts on the coastal zone. These wave driven processes can impact on many aspects of the PICT coastal environment, including: coastal flooding during storm wave events; coastal erosion, both during episodic storm events and due to long term changes in integrated wave climate; characterisation of reef morphology and marine habitat/species distribution; flushing and circulation of lagoons; and transport and energy solutions. Pacific Island Countries and Territories (PICTs) are arguably more vulnerable to variability and change in the surface wind-wave climate than sea-level rise. Future coastal vulnerability assessments for the region must consider potential changes in wave properties, together with the influence of mean sea-level rise and changes to other sea-level extremes. In order to support such assessments, this project had two objectives: 1. Describe the current wave climate on the basis of existing information, including understanding the dominant modes of seasonal and inter-annual variability in the Pacific wave climate, and identifying gaps in current knowledge which require future attention. 2. Carry out a preliminary assessment of potential changes in Pacific basin wave climate under future climate scenarios. The literature describing the current knowledge of the Pacific basin wave climate has been reviewed, with focus on the region of the PICTs, including Hawaii. Throughout this region, a multi-modal wave spectrum is observed, with contributions from locally trade wind generated seas, swell waves generated in both the northern and southern hemisphere extratropical storm belts, and episodic tropical storm (cyclone) events (See Figure ES1). The relative fraction of each of these components depends on location. Islands located on or north of the equator have wave fields dominated by sea generated by north-easterly trade winds and the northern Pacific generated swell, although Islands located further eastwards (e.g., Hawaii) also experience southerly ocean swell. Islands located south of the equator have wave fields dominated by sea generated by south-easterly trade winds. Southern Pacific generated swell is also a major contributor to the wave climate at those islands which are not sheltered by other islands. For example, Samoa, French Polynesia and Fiji both experience southern ocean swell. Available long-term wave data for the Pacific region has been compiled, including available in- situ wave buoy records, model hindcast and reanalyses products, and satellite altimeter derived records. We have assessed these datasets to determine their ability to describe the observed wave climate in the region. The wind-wave climate of the Pacific Ocean • 30 July 2011, Version – Draft only 3 EXECUTIVE SUMMARY Figure ES1: The wind-wave climate in the region of the PICTs has several contributing components (multi-modal). To understand climatological variability of wave climate in the region, the response of each of these contributions must be understood. The in-situ collected wave buoy data held by SOPAC is a valuable dataset describing the wave field at selected locations within the PICTs. However, these data are limited to few locations, and have a maximum record length of 5 years. Consequently the data contain little information to identify the key modes of inter-annual (and decadal) wave climate variability. Only a small collection of these records contain directional information Longer term in-situ buoy records are available from within the Pacific basin, collected as part of the United States National Oceanographic and Atmospheric Administration National Buoy Data Centre (NOAA NBDC). These