IBI-CCS: a regional high-resolution model to simulate sea level in western Europe

[摘要] Projections of coastal sea level (SL) changes are ofgreat interest for coastal risk assessment and decision making. SLprojections are typically produced using global climate models (GCMs), whichcannot fully resolve SL changes at the coast due to their coarse resolutionand lack of representation of some relevant processes (tides, atmosphericsurface pressure forcing, waves). To overcome these limitations and refineprojections at regional scales, GCMs can be dynamically downscaled throughthe implementation of a high-resolution regional climate model (RCM). Inthis study, we developed the IBI-CCS (Iberian–Biscay–Ireland Climate ChangeScenarios) regional ocean model based on a 1 / 12 ∘ northeasternAtlantic Nucleus for European Modelling of the Ocean (NEMO) model configuration to dynamically downscaleCNRM-CM6-1-HR, a GCM with a 1 / 4 ∘ resolution oceanmodel component participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) by the Centre National de RecherchesMétéorologiques (CNRM). For a more complete representation of theprocesses driving coastal SL changes, tides and atmospheric surface pressureforcing are explicitly resolved in IBI-CCS in addition to the ocean generalcirculation. To limit the propagation of climate drifts and biases from theGCM into the regional simulations, several corrections are applied to theGCM fields used to force the RCM. The regional simulations are performedover the 1950 to 2100 period for two climate change scenarios (SSP1-2.6 andSSP5-8.5). To validate the dynamical downscaling method, the RCM and GCMsimulations are compared to reanalyses and observations over the 1993–2014period for a selection of ocean variables including SL. Results indicatethat large-scale performance of IBI-CCS is better than that of the GCMthanks to the corrections applied to the RCM. Extreme SLs are alsosatisfactorily represented in the IBI-CCS historical simulation. Comparisonof the RCM and GCM 21st century projections shows a limited impact ofincreased resolution ( 1 / 4 to 1 / 12 ∘ ) on SL changes.Overall, bias corrections have a moderate impact on projected coastal SLchanges, except in the Mediterranean Sea, where GCM biases were substantial.

[学科分类] 土木及结构工程学