A Comparison of GCM and RCM resolution Climate Projections in the Great Lakes - Effort, Efficiency, Uncertainty Considerations

English Abstract:

High-resolution output is a necessity for the Great Lakes region as conditions vary significantly in this heterogeneous environment. The procedures to obtain this spatially precise information are largely determined by financial resources of the end-user, whether a large well-funded municipality or a smaller community with no dedicated climate adaptation funding or staff. The latter better describes the majority of these stakeholders. In an ideal case, all users would have access and expert interpretation of many high-resolution RCM model runs, but this is not realistic.

This has led to many different approaches from high-resolution customized approaches, to much simpler delta approaches where multi-model GCM ensemble values are applied to a high resolution observed historical baseline climate. Both of these approaches generate high-resolution future projections, but a balance of many factors must be weighed. Often these factors are not fully appreciated by the non-expert end users of the information. Generally projections are practically limited by many GCM-scale projections (over 40 models in the last IPCC assessment) which can provide more comprehensive information on uncertainty versus a single (or few) high-resolution RCM projections which provide greatly reduced uncertainty estimates – and if one model run – no estimate at all.  The fundamental question is: Do simpler approaches provide valuable guidance within accepted uncertainty bounds in these heterogeneous environments?

Given the obstacle of financial resources available for climate adaptation in most locations, it is crucial that such studies go forward without the hurdle of cost, yet of course still be scientifically defensible. The comparative accuracy of final output of these two approaches is considered vis-à-vis the costs and benefits through a specific example location in Ontario.