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

Abstract

The projected climate change signals of a five-member high resolution ensemble, based on two global climate models (GCMs: ECHAM5 and CCCma3) and two regional climate models (RCMs: CLM and WRF) are analysed in this paper (Part II of a two part paper). In Part I the performance of the models for the control period are presented. The RCMs use a two nest procedure over Europe and Germany with a final spatial resolution of 7 km to downscale the GCM simulations for the present and future A1B scenario (2021-2050) time periods. The ensemble was extended by earlier simulations with the RCM REMO (driven by ECHAM5, two realisations) at a slightly coarser resolution. The climate change signals are evaluated and tested for significance for mean values and the seasonal cycles of temperature and precipitation, as well as for the intensity distribution of precipitation and the numbers of dry days and dry periods. All GCMs project a significant warming over Europe on seasonal and annual scales and the projected warming of the GCMs is retained in both nests of the RCMs, however, with added small variations. The mean warming over Germany of all ensemble members for the fine nest is in the range of 0.8 and 1.3 K with an average of 1.1 K. For mean annual precipitation the climate change signal varies in the range of -2 to 9 % over Germany within the ensemble. Changes in the number of wet days are projected in the range of ±4 % on the annual scale for the future time period. For the probability distribution of precipitation intensity, a decrease of lower intensities and an increase of moderate and higher intensities is projected by most ensemble members. For the mean values, the results indicate that the projected temperature change signal is caused mainly by the GCM and its initial condition (realisation), with little impact from the RCM. For precipitation, in addition, the RCM affects the climate change signal significantly.

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

“…Meanwhile, already for the end of the twentieth century Boberg et al (2010) found a change in the probability density function (PDF) of simulated precipitation with increase in the more intense events and a decrease in light and moderate rain. For Germany, a similar trend is confirmed regarding the precipitation intensities for the near future (2021-2050Wagner et al 2012), while the decrease in mean precipitation is found not significant in summer. A consistent reduction in cloudiness, snow cover and soil water content is projected over Europe together with an increasing trend in atmospheric moisture, reaching 10-20 % by the end of the century (Giorgi et al 2004).…”

“…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.…”

“…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.…”

“…Its fifth version, ECHAM5 (Roeckner et al 2003), has been widely used for studies on the climate change signal (e.g. Reichler and Kim 2008;Feldmann et al 2013;Wagner et al 2012). Here, for the recent past only twentieth century anthropogenic greenhouse gas forcing is considered (Roeckner et al 2006), and for the future the IPCC SRES A1B forcing scenario is used (Nakicenovic et al 2000).…”

“…In Germany, an annual increase of ~1 K is projected for the next decades . The climate change signal of temperature is mainly driven by the selected GCM and emission scenario used, while the role of RCMs becomes crucial when dealing with more complex processes such as precipitation, especially in summer when convection becomes dominant (Déqué et al 2007;Wagner et al 2012). Until the end of the century, RCMs project a general decrease in summer mean precipitation over western and southern Europe, which could be due to a northward deflection of Atlantic storms bringing wetter conditions to northern Europe ).…”