Changes in the mean and extreme geostrophic wind speeds in Northern Europe until 2100 based on nine global climate models

摘要

This study aims at analyzing the mean and extreme geostrophic wind speeds in Northern Europe. The analyses are based on nine global climate models and the Special Report on Emission Scenarios (SRES) A1B, A2 and B1 scenarios. The time frames studied consist of the baseline 1971-2000 and the future periods 2046-2065 and 2081-2100. The SRES scenarios are considered both separately and combined. The extremes are calculated for the September-April period for various return periods. The analysis is done by applying the program R and the Generalized Extreme Value -methodology. All projections indicate that both the mean and extreme geostrophic wind speeds will increase in the southern and eastern parts of Northern Europe and decrease over the Norwegian Sea in September-April. The change over the ocean is pronounced already in 2046-2065, over the continents in 2081-2100. For the model mean, the smallest change (2-6%) was projected under the B1 and the largest (4-10%) under the A1B and A2 scenarios. However, spread among the individual global circulation models (GCMs) was fairly large. The ratios between the return level estimates for various return periods and the annual maximum wind speeds were found nearly homogeneously independent of the time frame studied. For the baseline and future periods, the extreme winds occurring once in 10 or 50 years were 13% ± 2% and 22% ± 5% stronger than the mean annual maxima, respectively. The present findings serve as support for risk assessment such as required when planning the forest management practices.