Estimates of changes in surface wind and temperature extremes in southwestern Norway using dynamical downscaling method under future climate

Abstract

Extreme surface winds and temperatures were estimated by the dynamical downscaling method combined with the generalized extreme value theory for the construction of Hardanger Suspension Bridge and the maintenance of Sotra Bridge in southwestern Norway. The Weather Research and Forecasting Model was used to downscale the Norwegian Earth System Model data from 2.5° × 1.8° to 1 km × 1 km horizontal grids. Simulations were performed for the control period, the 1990s, and the projection period, the 2050s, under the RCP8.5 radiative forcing scenario. Monthly maximum winds were compared with observations at three nearby observation stations for the warm and the cold seasons as well as the annual period. The simulated extreme wind distributions are in good agreement with the observed distributions at the coastal area, but have systematic positive deviations on the mountain. An extrapolation method was used to project extreme winds in the early and the late this century. Comparison of the simulated extreme winds between the 1990s and the 2050s shows that future extreme winds are unlikely to change with statistical significance during the cold season, but tend to decrease at mountainous and coastal areas with statistical significance during the warm season. They are possibly the reflections of the shift in the regional storm activities associated with the changes of the North Atlantic Oscillations and the effects of the local mountain topography. For surface maximum and minimum temperatures, the model can well reproduce the spreads of the pdf distributions. Both distributions shift towards higher temperatures in the 2050s. Keywords: Regional climate, Dynamical downscaling, WRF model, Extreme wind, Extreme surface temperature, Complex terrain