Hybrid downscaling of wind climates over the eastern USA

Abstract

Weibull distribution parameters (scale and shape) of wind speeds at 85 stations over the eastern USA are downscaled from distribution parameters of large-scale climate variables drawn from both global and regional models. A probabilistic statistical downscaling approach when applied in hybrid downscaling (combining dynamical and statistical downscaling), exhibits skill in reproducing the macro-scale variability in wind climates in independent data. However, use of predictors from a regional climate model (RCM) run at 50 km resolution does not substantially improve the downscaling results over those obtained when direct output from the parent atmosphere ocean general circulation model (AOGCM) run at approximately 200 km resolution is used for the predictors. The technique is applied to develop projections of mean and 90th percentile wind speeds based on output from six sets of RCM simulations. Projected differences in the mean and 90th percentile wind speeds over the eastern USA for 2041–2060 relative to 1981–1998 are of very modest magnitude (i.e. <5% of the value during 1981–1998), and are smaller than the inherent downscaling uncertainty. The implied near-term stability of wind climates is consistent with analysis of wind speeds directly simulated by RCMs.