Sensitivity of European extreme daily temperature return levels to projected changes in mean and variance

Abstract

Both the mean and variance in European daily temperature are projected to change in the future. Such a change affects also the return period of extreme events. The aim of this study is to investigate the relationship between changes in statistical moments of the daily temperature distribution and return levels of warm extremes. For this purpose, the distributions of daily maximum temperature during summer and daily minimum temperature during winter for the control period 1961–1990 are scaled and shifted by the expected changes in the mean and variance. The estimated return levels of warm summer day and warm winter night extremes are then compared with the regional climate model projections for the scenario period 2070–2099. This study shows that changes in return levels of warm summer and winter extremes can be approximated as a simple shift of the full temperature distribution for one quarter to two thirds of Europe across all examined climate models. In other areas, changes in the variance have to be considered. When for a particular temperature distribution, the lowermost and uppermost percentiles change at different rates, the temperature variability changes asymmetrically. Therefore, scaling the control temperature distribution symmetrically, i.e., with the second central moments, does not always lead to an improvement of the estimates compared with the location-adjusted return level estimates. Nevertheless, the study shows that if the asymmetry in the change in scale is accounted for, then the location-scale-adjusted return levels perform better than the location-adjusted return levels over most areas.