Projecting Future High Flows on King County Rivers: Phase 2


Mauger, G.S. and J.S. Won. 2020. Projecting Future High Flows on King County Rivers: Phase 2 Results. Report prepared for King County. Climate Impacts Group, University of Washington.


Phase 1 of the current study evaluated future peak flows on the Green, Snoqualmie, and South Fork Skykomish rivers using two new regional climate model projections of future climate. Recent work has shown that regional climate model projections are better at capturing future changes in heavy rain events and are therefore likely to provide more accurate estimates of the changes in future floods. The findings from Phase 1 confirmed that two projections are not enough to reliably bracket the range in future flood magnitudes. The University of Washington has since produced an additional 11 projections. Combined with the two original simulations, the result is an ensemble of 13 regional climate model projections. The purpose of this study, Phase 2 of the work, is to evaluate the implications for flooding with this expanded set of scenarios using the same methodology used in the Phase 1 work. A secondary objective is to document improvements in the methodology that could further improve the accuracy of the projections in a possible Phase 3 effort.