Abstract
Abstract The IPCC Fifth Assessment Report highlighted large uncertainty in European precipitation changes in the coming century. This paper investigates the sources of intermodel differences using CMIP5 model European precipitation data. The contribution of atmospheric circulation to differences in precipitation trends is investigated by applying cluster analysis to daily mean sea level pressure (MSLP) data. The resulting classification is used to reconstruct monthly precipitation time series, thereby isolating the component of precipitation variability directly related to atmospheric circulation. Reconstructed observed precipitation and reconstructions of simulated historical and projection data are well correlated with the original precipitation series, showing that circulation variability accounts for a substantial fraction of European precipitation variability. Removing the reconstructed precipitation from the original precipitation leaves a residual component related to noncirculation effects (and any small remaining circulation effects). Intermodel spread in residual future European precipitation trends is substantially reduced compared to the spread of the original precipitation trends. Uncertainty in future atmospheric circulation accounts for more than half of the intermodel variance in twenty-first-century precipitation trends for winter months for both northern and southern Europe. Furthermore, a substantial part of this variance is related to different forced dynamical responses in different models and is therefore potentially reducible. These results highlight the importance of understanding future changes in atmospheric dynamics in achieving more robust projections of regional climate change. Finally, the possible dynamical mechanisms that may drive the future differences in regional circulation and precipitation are illustrated by examining simulated teleconnections with tropical precipitation.
Highlights
The large social and economic impacts of flooding events such as the extreme winters of 2013/14 (Huntingford et al 2014) and 2015/16 (Scaife et al 2017) in the United Kingdom underline the importance of understanding future trends in regional precipitation and their drivers
We have developed a technique to reconstruct precipitation from atmospheric circulation data to gauge how much of the substantial uncertainty in future model projections of European precipitation is a result of uncertainty in projected circulation patterns
The reconstructed precipitation series are strongly correlated with the original precipitation, showing that much of the precipitation variability is related to large-scale circulation patterns, in winter
Summary
The large social and economic impacts of flooding events such as the extreme winters of 2013/14 (Huntingford et al 2014) and 2015/16 (Scaife et al 2017) in the United Kingdom underline the importance of understanding future trends in regional precipitation and their drivers. The lack of consensus for European changes means that multimodel mean changes are only significant compared to internal model variability in parts of southern Europe (Fig. 12.18 in Collins et al 2013) This suggests that much of the uncertainty in the CMIP5 projections of European precipitation could be linked to uncertainty in regional atmospheric circulation, including the circulation response to climate forcing and circulation changes due to internal variability. We present a method for reconstructing European precipitation based on circulation, so that precipitation can be partitioned into circulation-related and non-circulation-related components This allows us to quantify the contribution of dynamical uncertainty to the spread in projections of future precipitation in Europe.
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