| ABSTRACT | Since the Mediterranean area is a highly vulnerable region with respect to droughts and heavy precipitation, reliable assessments of the future development of precipitation behavior are of utmost importance. A novel statistical downscaling approach was developed to assess future regional precipitation extremes. The approach allows for non-stationarities in the predictors-precipitation relationships for assessing future precipitation extremes. It is based on 31 year contiguous calibration periods each shifted by one year. Consequently, a statistical model ensemble becomes available, with the number of established regression models corresponding to the number of years within the entire time series. By means of the regression model ensemble, first, the range of estimations for a stationary model setup was assessed. Subsequently, a selection process was performed in order to find the most suitable model for assessing future precipitation extremes under non-stationary conditions.
Results show that the estimated quantiles of heavy precipitation (90th, 95th, 99th quantiles) of the non-stationary approach are within the range of estimations of the stationary regression model ensemble but sometimes, with respect to the historical GCM runs, absolute and relative changes outperform or undercut the estimations of the stationary approach. Although the direction of both approaches do not differ, differences appear with respect to the amount of change. For example under the RCP8.5 scenario the direction of change of the 90th quantile in autumn at Safed weather station (Israel) is rather the same but decreases are over 10% lower for the non-stationary approach than under consideration of a stationary model setup.
Overall, the progression of the analyzed quantiles during the course of the 21st century strongly depends on season and region within the Mediterranean area. In autumn, with the exception of the eastern coast of the Iberian Peninsula, all regions show partly significant decreases of heavy precipitation until the end of the 21st century. In winter, especially the northern parts of the central Mediterranean area exhibit significant increases and smaller increases could be observed for northern Spain. Strongest decreases could be observed for the Levante region in spring, a region where decreases are projected throughout the year. |