Sources of water vapour contributing to the Elbe flood in August 2002—A tagging study in a mesoscale model

Abstract

ABSTRACT:In this study we investigate the contribution of various moisture sources to the Elbe flood that occurred in Central Europe during August 2002. An 8-day simulation with the mesoscale numerical weather prediction model CHRM, including newly implemented water vapour tracers, has been performed. According to the simulation, rather than drawing moisture from one single dominant source region, water vapour from widely separated moisture sources contributed to the extreme precipitation in the most affected area, notably at distinct, subsequent periods of time, and each in significant amounts. These moisture sources include the Atlantic and Mediterranean ocean areas inside the model domain, evapotranspiration from land areas, and long-range advection from subtropical areas outside the model domain.The results highlight the importance of the concurrent upper-level circulation and the mesoscale flow structures associated with the cyclone for producing extreme precipitation in parts of Germany, Austria, and the Czech Republic during that period. Furthermore, the numerical and technical problems of implementing water vapour tracers into a limited-area model are discussed, including conservative tracer advection, initialization, boundary treatment, and the handling of precipitation parametrizations. An evaluation of the consistency of the method in terms of water vapour, cloud water, and precipitation is provided, with generally satisfying results. The model with its detailed water vapour tracer implementation can now be used for further case-studies and climatological simulations, and serve as a reference for evaluating the performance of other moisture tracking methods, such as those based on backward trajectories.

Atmospheric processes triggering the central European floods in June 2013

“…Elbe and Danube catchments (Ulbrich et al, 2003a, b;James et al, 2004;Sodemann et al, 2009), and in 2005 again in the catchments of Danube and the Swiss Rhine tributary Aare (Zängl, 2007a, b;Hohenegger et al, 2008). All these recent floods happened in the summer and their meteorological setting involved extratropical cyclones of type "Vb", which refers to a special category of cyclone tracks in Europe (van Bebber, 1891).…”

“…Similarly, for an eastern European flood event in May 2010, Winschall et al (2014) found continental moisture sources to be crucial for the heavy precipitation in addition to important moisture sources in the North Atlantic and Mediterranean. Also James et al (2004) stressed the importance of continental moisture sources for the 2002 Elbe flood, although this event was characterised by a variety of moisture sources (Sodemann et al, 2009). …”

Impact of North Atlantic evaporation hot spots on southern Alpine heavy precipitation events

“…In this study we use the limited-area model CHRM with a water vapour tagging technique implemented by Sodemann et al (2009). See also Sodemann et al (2009) for an overview of previous water vapour tagging applications.…”

“…For the parametrized subgridscale processes that affect phase changes like stratiform and convective precipitation, all transfer rates of tagged moisture are considered proportional to the fraction of tagged water and the respective total transfer rate. For more technical information on the tagging implementation see Sodemann (2006) and Sodemann et al (2009). The only difference of the tagging implementations used in this study is a corrected bug in the parametrization of the evapotranspiration of tagged water vapour from land surfaces, which leads to an increase of tagged land evapotranspiration compared to the previous version.…”

“…Milelli et al (2006) investigated this event and concluded that a flow of moist air from the south towards the Alps ahead of a broad upper-level trough and the subsequent lifting led to the heavy precipitation. A water vapour tagging technique implemented by Sodemann et al (2009) in the climate high-resolution model (CHRM) will be used to determine the water sources for this Piedmont flooding event. The special intention of this paper is to investigate the extent to which moisture evaporated from the North Atlantic contributed to this particular event of heavy precipitation in the Piedmont and, in a second, more climatological part of this study, to heavy precipitation events on the Alpine south side in general.…”