Projection of occurrence of extreme dry-wet years and seasons in Europe with stationary and nonstationary Standardized Precipitation Indices

The probabilities of the occurrence of extreme dry/wet years and seasons in Europe are estimated by using two ways of the Standardized Precipitation Index (SPI and SPI-GEV) and the Standardized Nonstationary Precipitation Index (SnsPI). The latter is defined as the SPI by fitting precipitation data with a nonstationary Gamma distribution in order to model the precipitation time dependence under climate change. Bias-corrected daily precipitation outputs from five different regional climate models (RCMs) provided by the ENSEMBLES project are used. The five RCMs are selected so as to represent the main statistical properties of the whole ENSEMBLES set and the most extreme deviation from the ensemble mean. All indicators are calculated for the ensemble of the five models over the period 1971-2098. Results show that under global warming, climate in Europe will significantly change from its current state with the probability of the occurrence of extreme dry and wet years and seasons increasing, respectively, over southern dry and northern wet regions. Comparing nonstationary and stationary indices, the SnsPI is found to be more robust than the common SPI in the prediction of precipitation changes with multimodel ensembles.