Current climate-change projections from Global Circulation Models (GCMs), as summarized in the latest IPCC assessment report, have limited application to Hawaii and the Pacific Islands. Most very long climate forecasts have been performed at large horizontal spatial grid resolutions of 200 to 300 km. Without further downscaling analyses, predictions from GCM’s are not useful as the basis for planning adaptation measures at the regional and island scale. By downscaling a GCM’s predictions, researchers get more regionally applicable predictions of variables. In this research, downscaling studies will be conducted in an effort to produce the best guidance possible on long-term climate changes expected in Hawaii and other islands in the region.
The results will be disseminated to decision makers and to the general public through stakeholder interactions and outreach efforts. The results will also be used as input to a hydroclimatic research project concerning sustainability of island water resources.
Regional projections for Hawaii and the Pacific Islands require input from global coupled ocean-atmosphere model projections. A large suite of 21st century climate projections for different emission scenarios and different global climate models was made available as part of the process leading to the latest IPCC assessment report (AR5). A similar effort (Coupled Model Intercomparison Project 5 or CMIP5) has more advanced models and projections on 10 to 30 year time frames. Appropriate AR5 and CMIP5 models will be used to represent climate processes in the tropical and subtropical Pacific region.
One approach to producing downscaled data for the Pacific Islands is to use statistical relationships between local variables such as rainfall and the regional-scale weather patterns. If the relationships determined from present-day climate observations can be assumed to hold for future climate conditions, then these relationships can be used to downscale coarse climate projections.
Current work at IPRC using linear statistical downscaling of seasonal rainfall for the main Hawaiian Islands will be extended to consider nonlinear relationships. Downscaled climate data will be extended to consider the distribution of rainfall intensities associated with extreme events throughout the Pacific islands in collaboration with efforts underway in the PRICIP project.
Limited-Area Model Simulations
Statistical approaches will be complemented by high-resolution atmospheric numerical modeling at IPRC. An initial assessment will be made using results provided to IPRC from the Climate Research Department of the Japan Meteorological Research Institute (MRI).
- These results provide, for the first time, a global warming forecast with a model that has a somewhat realistic representation of the coastlines and topography of the main Hawaiian Islands. These data can be used to see how well statistical downscaling approaches work in predicting the model simulated changes over Hawaii (at least at ~20 km resolution).
- IPRC will conduct numerical climate-change projection experiments for both current and global warming climate conditions using a multiply-nested regional atmospheric modeling system (WRF) with high ~0.5 to 1 km resolution over Hawaii.
- Detailed maps of surface temperature, surface wind and rainfall statistics for the island of Maui will be conducted to provide input to the hydrological modeling project.
Header image: The 10-year average change in the underlying global warming signals in sea surface temperatures (DSST) for the three global warming cases A–C, compared with present- day conditions (1999–2008). (Source: Lauer et al., 2010)