Abstract
Abstract. Extreme weather events can have large impacts on society and, in many regions, are expected to change in frequency and intensity with climate change. Owing to the relatively short observational record, climate models are useful tools as they allow for generation of a larger sample of extreme events, to attribute recent events to anthropogenic climate change, and to project changes in such events into the future. The modelling system known as weather@home, consisting of a global climate model (GCM) with a nested regional climate model (RCM) and driven by sea surface temperatures, allows one to generate a very large ensemble with the help of volunteer distributed computing. This is a key tool to understanding many aspects of extreme events. Here, a new version of the weather@home system (weather@home 2) with a higher-resolution RCM over Europe is documented and a broad validation of the climate is performed. The new model includes a more recent land-surface scheme in both GCM and RCM, where subgrid-scale land-surface heterogeneity is newly represented using tiles, and an increase in RCM resolution from 50 to 25 km. The GCM performs similarly to the previous version, with some improvements in the representation of mean climate. The European RCM temperature biases are overall reduced, in particular the warm bias over eastern Europe, but large biases remain. Precipitation is improved over the Alps in summer, with mixed changes in other regions and seasons. The model is shown to represent the main classes of regional extreme events reasonably well and shows a good sensitivity to its drivers. In particular, given the improvements in this version of the weather@home system, it is likely that more reliable statements can be made with regards to impact statements, especially at more localized scales.
Highlights
Anthropogenic climate change due to increased greenhouse gas concentrations in the atmosphere poses numerous threats to society (IPCC, 2013)
It consists of an atmospheric global climate model (GCM), HadAM3P, that is downscaled to a higher resolution over a limited domain by its regional climate model (RCM) equivalent, HadRM3P
The new version of weather@home presented and validated in this paper is a powerful tool for the study of extreme weather events
Summary
Anthropogenic climate change due to increased greenhouse gas concentrations in the atmosphere poses numerous threats to society (IPCC, 2013). Large ensembles of global climate models (GCMs) allow derivation of multiple sequences of weather patterns and a substantial number of associated extreme events Dynamical downscaling of these GCM simulations by regional climate models (RCMs, Giorgi, 2006) can provide more spatially detailed information, which can be very valuable for the investigation of localized impacts of extreme weather events. Consisting of a GCM with prescribed sea surface temperatures (SSTs) and sea ice and a nested RCM over a region of interest, it leverages the computing power of volunteers around the world to generate very large ensembles of GCM–RCM simulations This is useful for the investigation of extreme weather events, and weather@home has been used successfully for the attribution of many extreme weather events (e.g. Pall et al, 2011; Otto et al, 2012) as well as their impacts, such as flooding-related property damages (Schaller et al, 2016) and heat-related mortality (Mitchell et al, 2016b).
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