High resolution regional climate model simulations for Germany: part I—validation

Abstract

A five-member ensemble of regional climate model (RCM) simulations for Europe, with a high resolution nest over Germany, is analysed in a two-part paper: Part I (the current paper) presents the performance of the models for the control period, and Part II presents results for near future climate changes. Two different RCMs, CLM and WRF, were used to dynamically downscale simulations with the ECHAM5 and CCCma3 global climate models (GCMs), as well as the ERA40-reanalysis for validation purposes. Three realisations of ECHAM5 and one with CCCma3 were downscaled with CLM, and additionally one realisation of ECHAM5 with WRF. An approach of double nesting was used, first to an approximately 50 km resolution for entire Europe and then to a domain of approximately 7 km covering Germany and its near surroundings. Comparisons of the fine nest simulations are made to earlier high resolution simulations for the region with the RCM REMO for two ECHAM5 realisations. Biases from the GCMs are generally carried over to the RCMs, which can then reduce or worsen the biases. The bias of the coarse nest is carried over to the fine nest but does not change in amplitude, i.e. the fine nest does not add additional mean bias to the simulations. The spatial pattern of the wet bias over central Europe is similar for all CLM simulations, and leads to a stronger bias in the fine nest simulations compared to that of WRF and REMO. The wet bias in the CLM model is found to be due to a too frequent drizzle, but for higher intensities the distributions are well simulated with both CLM and WRF at the 50 and 7 km resolutions. Also the spatial distributions are close to high resolution gridded observations. The REMO model has low biases in the domain averages over Germany and no drizzle problem, but has a shift in the mean precipitation patterns and a strong overestimation of higher intensities. The GCMs perform well in simulating the intensity distribution of precipitation at their own resolution, but the RCMs add value to the distributions when compared to observations at the fine nest resolution.

High resolution regional climate model simulations for Germany: Part II—projected climate changes

“…from PRUDENCE . Furthermore, the projected temperature range (areal mean between 1.1 and 1.5 K) is also narrower than the bias range (-1 to -5 K for areal means) analysed in Berg et al (2012). Besides the overall warming, the patterns and magnitudes of the projected changes show larger impact of the GCM and its realisation on the simulation results compared to the RCM, which agrees with previous results (e.g.…”

Climate change in the next 30 years: What can a convection-permitting model tell us that we did not already know?

“…In particular, Fosser (2014) found that compared to ERA40 driven simulations, ECHAM5 driven simulations highly overestimate the number of wet days especially in winter, as also pointed out by Berg et al (2012) and Feldmann et al (2008). This leads to a strong overestimation in daily mean precipitation especially at coarser resolution.…”

“…at 0.025° (~2.8 km, 140 × 116 grid points), concentrates on the state of Baden-Württemberg in southwestern Germany. The coarser nest at 50 km resolution and CLM7 have already been validated and investigated in terms of climate change respectively by Berg et al (2012) and Wagner et al (2012). They found that the two resolutions perform similarly although added value for CLM7 was found in terms of spatial pattern and PDF of higher precipitation intensities.…”

“…Thus, the two 30 year periods investigated are 1971-2000 for the past and 2021-2050 for the future. Berg et al (2012) investigated three different realizations of the ECHAM5 model for the control period, and found limited differences in mean temperature and precipitation for central Europe, although realization one showed slightly higher probabilities for the most extreme precipitation events and is therefore selected for further downscaling here. Wagner et al (2012) investigated the climate change of the three realizations and again found strong similarities between the realizations, with some minor spatial differences in the patterns.…”

Grenzen und Herausforderungen der regionalen Klimamodellierung

“…Abb. 5.2; Berg et al 2013). Simulationen im Projekt EURO-CORDEX zeigen: Erhöht man die Auflösung der Regionalmodelle von 50 auf 12,5 km, passen die Modellergebnisse sowohl hinsichtlich der räumlichen Verteilung der Niederschläge als auch der räumlichen Variabilität über Deutschland besser zu den Beobachtungen (Prein et al 2015).…”