Climate change in the next 30\xa0years: What can a convection-permitting model tell us that we did not already know?

G Fosser,P Berg,S Khodayar

doi:10.1007/s00382-016-3186-4

Abstract

To investigate the climate change in the next 30 years over a complex terrain in southwestern Germany, simulations performed with the regional climate model COSMO-CLM at convection-permitting resolution are compared to simulations at 7 km resolution with parameterised convection. An earlier study has shown the main benefits of convection-permitting resolution in the hourly statistics and the diurnal cycle of precipitation intensities. Here, we investigate whether the improved simulation of precipitation in the convection-permitting model is affecting future climate projections in summer. Overall, the future scenario (ECHAM5 with A1B forcing) brings weak changes in mean precipitation, but stronger hourly intensities in the morning and less frequent but more intense daily precipitation. The two model simulations produce similar changes in climate, despite differences in their physical characteristics linked to the formation of convective precipitation. A significant increase in the morning precipitation probably due to large-scale forced convection is found when considering only the most extreme events (above 50 mm/day). In this case, even the diurnal cycles of precipitation and convection-related indices are similar between resolutions, leading to the conclusion that the 7 km model sufficiently resolves the most extreme convective events. In this region and time periods, the 7 km resolution is deemed sufficient for most assessments of near future precipitation change. However, conclusions could be dependent on the characteristics of the region of investigation.

Highlights

Knowledge of the regional trends of the precipitation patterns under climate change is crucial to develop effective adaptation measures
The climate change signal of temperature is mainly driven by the selected global climate models (GCMs) and emission scenario used, while the role of Regional climate models (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)
Analysis performed for the Wagner et al (2012) paper shows similar decreases in mean precipitation in JJA for all three realizations of ECHAM5 downscaled by CLM7, and cases of increases in precipitation seems to be more related to natural variability than a result of climate change

Summary

Introduction

Knowledge of the regional trends of the precipitation patterns under climate change is crucial to develop effective adaptation measures. 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). For Germany, a similar trend is confirmed regarding the precipitation intensities for the near future (2021–2050; Wagner 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). A rise of ~20 % on the annual scale in the number of dry days and dry periods is projected for southwestern Germany in line with the European trend (Wagner et al 2012)

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