Extreme dry and wet events in Iceland: Observations, simulations and scenarios

Monthly extremes of dryness and wetness in Iceland are analysed based on the standardised precipitation index (SPI). The analysis is performed for observations and four sets of coupled atmosphere-ocean climate model simulations (ECHAM5.MPI-OM) to link water cycle extremes in Iceland with regional atmospheric flow patterns and to estimate and evaluate future changes. The following results are obtained: (i) SPI extremes are linked with a Europe-Greenland Index (EGI) describing south-westerly flow anomalies by a dipole and the related geopotential height differences. The good agreement between the observed statistics and transient 20th century simulations encourages analysis of future climate projections. (ii) Comparison of the 21st century A1B-scenario with the pre-industrial climate reveals significant and large differences: While extremes of dryness hardly change, extremely wet conditions increase in winter and spring. As there is no flow intensification and cyclone density decreases, the cause maybe found in air moisture raising in a warmer climate.