ALBERT

Description: The destructive power of extreme natural events is causing more and more material damages and losses of life. With the number of natural disasters globally increasing, coordinated disaster management is getting more important. During the past years, several research centers within the Helmholtz Association established extensive expertise in the field of disaster management. Via the Natural Disaster Networking Platform (NaDiNe), this expertise will be provided a larger number of users beyond the realm of scientific facilities.

Description: An innovative technique has been developed to assess moisture sources contributing to precipitation. It represents an advance with respect to previously developed methodologies because it allows to discriminate more effectively between terrestrial versus oceanic sources, and also to detect with greater precision the relative importance of remote versus local sources together with the sequence of evaporation associated with a rainfall event. It is based upon the use of a mesoscale model to simulate a selected precipitation episode and a Lagrangian trajectory model to evaluate three-dimensional back-trajectories in order to track the vapor parcels transporting the target precipitation to their surface evaporative sources. An extreme sequence of rainfall events occurred over central Europe between August 11th and 13th is chosen to put the methodology into test. A domain centered in the region and spanning 6372 km in the W-E direction and 5940 km in the N-S direction is chosen to assess moisture sources. Results show the evolving role of various sources throughout the duration of the event, indicating that they shift from the southern to northern and eastern source regions, while a simultaneous decrease of marine sources with respect to terrestrial sources occurs from the onset of the event to its ending phase. The capability of discriminating moisture sources with precision is an important requirement to better understand the mechanisms of extreme rainfalls.

Description: This article investigates an extreme rainfall event occurred over wide areas of central Europe on August 11-13, 2002. By using a synergistic approach that includes regional modeling, air mass tracking, and observational data sets, the importance of moisture accumulation processes in the Western Mediterranean basin (WMB) is acknowledged as an important mechanism responsible for the magnitude of this event. The RAMS-HYPACT modeling system is used to track air masses from potential marine sources of evaporation. MODIS water vapor products, wind profilers and surface rain gauge measurements are used to substantiate our simulations. Results show that most of the precipitation occurring in central Europe during the initiation of the rainfall episode (August 11) came from vapor accumulated over 4 days (August 6-9) within the WMB: the vapor was transported, after the irruption of the Vb cyclone Ilse, through the Italian Peninsula and the Adriatic Sea, into the target area, causing the precipitation episode. On August 12 and 13 the marine sources of evaporation changed to include the north-Atlantic region. The north-African convergence region, the eastern Mediterranean and the Black Sea are revealed to be sources more related to the intense rainfall experienced in eastern Europe. The subsidence-related processes through which pollutants and water vapor can accumulate for several days in the WMB are shown to be very relevant for this event. The quantification of the evaporative sources, responsible for the extreme rainfall events in central Europe, and the relative importance of marine and terrestrial sources within a chosen regional domain are discussed in the companion following article.