Comparative Analysis of Continuous and Reinitialized Dynamical Downscaling in the North Atlantic and Surrounding Continents

Abstract. General Circulation Models provide comprehensive climate projections but are limited by coarse spatial resolution. To address this issue, Regional Climate Models are used for higher-resolution simulations, particularly to assess regional climate change impacts. This process, called dynamical downscaling, typically involves continuous simulations over a selected period. Alternatively, multiple reinitialized simulations over shorter intervals can be employed to minimize error accumulation and reduce computation time through parallel processing. However, this approach may hinder the development of certain atmospheric phenomena. In this study, the Weather Research and Forecasting model was used for continuous and daily reinitialized dynamical downscaling. Simulations were driven by ERA5 and Coupled Model Intercomparison Project Phase 6 data at 1° and 1.25° spatial resolution, respectively, covering 115° W–40° E in longitude and 20° N–60° N latitude, and downscaled to 20-km resolution. The results were evaluated against ERA5 data at 0.25° resolution to assess accuracy. The analysis focused on wind speed, temperature, humidity, precipitation, surface pressure, and solar radiation. Overall, both techniques demonstrated good to excellent correlation with the reference data. However, neither method reliably captured wind speed nor surface pressure in mountainous areas. In ERA5-driven simulations, the reinitialized technique performed better than the continuous for air temperature and humidity in coastal regions, whereas the continuous approach showed a slight advantage in estimating solar radiation across all surfaces. For CMIP6-driven simulations, both downscaling techniques produced similar results, except for solar radiation and over land, where the continuous method demonstrated marginally better performance. Considering the significantly lower computational cost of the reinitialized method – approximately 30 times less in this study – it is recommended as the preferred approach when its performance is comparable to or better than that of the continuous method.