Surface wind waves were identified in the Intergovernmental Panel for Climate Change (IPCC) Fourth Assessment Report (AR4) as one of the key drivers in the coastal zone, but little information was available on projected changes under future climate scenarios. The main focus was on the influence of sea-level rise and inundation effects. The IPCC Working Group II recognized that risks to coastal population and ecosystems require inclusion of a broader range of coastal drivers of change. One of the key drivers, which has received insufficient attention to date, is wind-waves.
The JCOMM and WCRP jointly supported Coordinated Ocean Wave Climate Projections (COWCLIP) workshop, held at WMO in Geneva, 11-13 April, 2011, provided a forum to develop a coordinated approach to wave projection studies to maximize their benefit as input into the IPCC Fifth Assessment Report.
Several methods of deriving wave climate projections are being developed, including dynamical and statistical approaches. In the dynamical method, surface forcing taken from climate models is used to force a spectral wave model. Bias-adjustment (of waves or of forcing winds) may be used to improve current wave climate representation, assuming a time invariant bias adjustment to derive future projections. The statistical approach uses current climate reanalyzes (atmospheric and wave) to establish a statistical relationship between the predictor (e.g., MSLP, 10-m winds) and the predictand (e.g., most commonly Hs, but other variables are being considered). The statistical relationship established is then applied to projections of the predictor taken from climate models to derive projections of the predictand.
COWCLIP aims to generate wave climate projections (ultimately of global extent) and aid comprehensive assessments of their cascading uncertainty by:
- Providing a systematic, community-based framework and infrastructure to support validation, intercomparison, documentation and data access for wave climate projections forced from CMIP5 datasets;
- To describe best practice for regional wave climate projections, and ;
- Engaging interests of the wave community into the wider climate community and ultimately developing coupled wind-wave Atmosphere-Ocean global climate models to support quantification of wind-wave driven feedback in the coupled climate system.
- Workshop presentation and discussion sessions were focused to identify key research questions and recommendations against four themes:
- Global wave projections
Regional wave projections
Coupling of wind-waves into coupled climate models
Historical wave climate variability and change
A key recommended objective of COWCLIP is coordination of global wave projections for intercomparing between international research groups, to understand uncertainty within the community ensemble of wave climate projections. Initial intercomparing experiments are being undertaken with a view to include wave parameters in greater detail in the IPCC AR5. The long-term COWCLIP goal is for waves to become a standard component of the coupled climate system, with waves coupled into climate models. Such an approach has advantages of (1) more physically representative parameterizations of key processes at the air-sea interface, and (2) removing the need for un-coupled wave model runs to generate wave information, needed by the impacts community but also simply providing additional parameters to assess the coupled climate system.