Regional climate modeling on European scales: a joint standard evaluation of the EURO-CORDEX RCM ensemble

Abstract

Abstract. EURO-CORDEX is an international climate downscaling initiative that aims to provide high-resolution climate scenarios for Europe. Here an evaluation of the ERAInterim-driven EURO-CORDEX regional climate model (RCM) ensemble is presented. The study documents the performance of the individual models in representing the basic spatiotemporal patterns of the European climate for the period 1989-2008. Model evaluation focuses on near-surface air temperature and precipitation, and uses the E-OBS data set as observational reference. The ensemble consists of 17 simulations carried out by seven different models at grid resolutions of 12 km (nine experiments) and 50 km (eight experiments). Several performance metrics computed from monthly and seasonal mean values are used to assess model performance over eight subdomains of the European continent. Results are compared to those for the ERA40-driven ENSEMBLES simulations.The analysis confirms the ability of RCMs to capture the basic features of the European climate, including its variability in space and time. But it also identifies nonnegligible deficiencies of the simulations for selected metrics, regions and seasons. Seasonally and regionally averaged temperature biases are mostly smaller than 1.5 • C, while precipitation biases are typically located in the ±40 % range. Some bias characteristics, such as a predominant cold and wet bias in most seasons and over most parts of Europe and a warm and dry summer bias over southern and southeastern Europe reflect common model biases. For seasonal mean quantities averaged over large European subdomains, no clear benefit of an increased spatial resolution (12 vs. 50 km) can be identified. The bias ranges of the EURO-CORDEX ensemble mostly correspond to those of the ENSEMBLES simulations, but some improvements in model performance can be identified (e.g., a less pronounced southern European warm summer bias). The temperature bias spread across different Published by Copernicus Publications on behalf of the European Geosciences Union. S. Kotlarski et al.: Regional climate modeling on European scalesconfigurations of one individual model can be of a similar magnitude as the spread across different models, demonstrating a strong influence of the specific choices in physical parameterizations and experimental setup on model performance. Based on a number of simply reproducible metrics, the present study quantifies the currently achievable accuracy of RCMs used for regional climate simulations over Europe and provides a quality standard for future model developments.

Scale dependency of regional climate modeling of current and future climate extremes in Germany

“…Giorgi et al (2016) demonstrated that dynamical downscaling to 12.5 km horizontal grid spacings over Europe introduces changes in climate that were not present in the forcing model. Kotlarski et al (2014) found that the ERA-Interim driven EURO-CORDEX (the European branch of CORDEX) ensemble simulations largely confirm RCM bias characteristics identified from the previous ENSEMBLES data. The results show future increases in climate extremes, such as heat waves, droughts, and heavy rainfall (Vautard et al 2013).…”

“…If the comparison was made with lower-resolution data sets, many features of the finer-resolution simulations would have been smoothed out (Vautard et al 2013). Although Kotlarski et al (2014) recommended interpolation to the coarsest-resolution grid, we employed the first approach to provide information for impact studies, as supported by Zollo et al (2015). This method allowed preservation of extreme values and temporal variability (Vautard et al 2013).…”

Mean and extreme precipitation over European river basins better simulated in a 25 km AGCM

“…The EURO-CORDEX simulations are driven by ERA-Interim reanalysis data and are available at a low (0.44 • ) and high (0.11 • ) resolution. Evaluating these simulations with respect to their representation of precipitation in Europe shows that for seasonal mean quantities averaged over large European subdomains no clear benefit of an increased spatial resolution can be identified (Kotlarski et al, 2014). At the same time, the 0.11 • simulations better reproduce spatial precipitation patterns (Casanueva et al, 2016) and this improvement is seen both for mean and moderately heavy (95 and 97.5 daily percentiles) precipitation (Fantini et al, 2016;Prein et al, 2016).…”

Grenzen und Herausforderungen der regionalen Klimamodellierung

“…Viele Untersuchungen haben gezeigt, dass unterschiedliche Regionalmodelle und Modellkonfigurationen den beobachteten Jahresgang und das klimatologische Mittel von Niederschlag, Temperatur und großräumiger Zirkulation über Europa mehrheitlich gut wiedergeben (Giorgi und Mearns 1999;Déqué et al 2007;Jacob et al 2007;Kotlarski et al 2014). Die Regionalmodelle reproduzieren dabei generell die großräumige Zirkulation des antreibenden Globalmodells (Vautard et al 2013).…”

“…Dies liegt weniger an den Unterschieden der Emissionsszenarien als u. a. an der höheren Auflösung der RCP-Simulationen und der Weiterentwicklung der Modelle Ban et al 2014;Kendon et al 2014). Oft zeigen Regionalmodelle bei steigender Auflösung höhere Niederschlagsmengen Kotlarski et al 2014), was -je nachdem ob das jeweilige Regionalmodell in gröberer Auflösung ein Niederschlagsdefizit oder einen Überschuss zeigt -zu realistischeren oder unrealistischeren Resultaten führt. Hinsichtlich der Dauer von Hitzeperioden finden Vautard et al (2013) …”