Rising Mediterranean Sea Surface Temperatures Amplify Extreme Summer Precipitation in Central Europe.

Claudia Volosciuk,Douglas Maraun,Natalia Tilinina,Sergey K Gulev,Mojib Latif,Vladimir A Semenov

doi:10.1038/srep32450

Abstract

The beginning of the 21st century was marked by a number of severe summer floods in Central Europe associated with extreme precipitation (e.g., Elbe 2002, Oder 2010 and Danube 2013). Extratropical storms, known as Vb-cyclones, cause summer extreme precipitation events over Central Europe and can thus lead to such floodings. Vb-cyclones develop over the Mediterranean Sea, which itself strongly warmed during recent decades. Here we investigate the influence of increased Mediterranean Sea surface temperature (SST) on extreme precipitation events in Central Europe. To this end, we carry out atmosphere model simulations forced by average Mediterranean SSTs during 1970–1999 and 2000–2012. Extreme precipitation events occurring on average every 20 summers in the warmer-SST-simulation (2000–2012) amplify along the Vb-cyclone track compared to those in the colder-SST-simulation (1970–1999), on average by 17% in Central Europe. The largest increase is located southeast of maximum precipitation for both simulated heavy events and historical Vb-events. The responsible physical mechanism is increased evaporation from and enhanced atmospheric moisture content over the Mediterranean Sea. The excess in precipitable water is transported from the Mediterranean Sea to Central Europe causing stronger precipitation extremes over that region. Our findings suggest that Mediterranean Sea surface warming amplifies Central European precipitation extremes.

Highlights

Flood producing summer precipitation extremes in Central Europe are often associated with Vb-cyclones[12,13,14], southerly west-east cyclone tracks and cut-off lows[15]
The locations of precipitation maxima that led to recent floods show high RL20S in all three experiments (Fig. 2), which gives us confidence in simulated extremes related to such synoptic situations
In comparison with the control experiment, summer RL20S are amplified in Central Europe along the Vb-cyclone track in both sensitivity experiments (Medwarm and Globwarm; Fig. 3), indicating stronger precipitation extremes even though simulated changes in summer-mean precipitation are much lower (

Summary

Introduction

Flood producing summer precipitation extremes in Central Europe are often associated with Vb-cyclones[12,13,14], southerly west-east cyclone tracks and cut-off lows[15]. The increase from the 1970–1999 to the 2000–2012 period in Mediterranean SSTs (annual mean: 0.62 °C, JJA mean: 0.86 °C) is considerably stronger compared to that of the global oceans (annual mean: 0.15 °C, JJA mean: 0.19 °C) These trends are projected (by the coupled model intercomparison project phase 5; CMIP5-ensemble) to continue www.nature.com/scientificreports/. The impact of sea surface warming on such heavy precipitation events cannot be studied in detail based on observations alone due to the relatively short period of recent high SSTs and given the rareness of extreme events. There are two major factors that may contribute to the intensification of cyclone-related summer precipitation extremes in Central Europe: changes in cyclone occurrence or pathway (dynamic changes) and changes in the amount of moisture carried by individual cyclones (thermodynamic changes). The amount of precipitation associated with Vb-cyclones is projected to increase[14,26], raising the question of where the additional precipitable water originates

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