Journal cover Journal topic
Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Nat. Hazards Earth Syst. Sci., 14, 1517-1530, 2014
http://www.nat-hazards-earth-syst-sci.net/14/1517/2014/
doi:10.5194/nhess-14-1517-2014
© Author(s) 2014. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
18 Jun 2014
Empirical atmospheric thresholds for debris flows and flash floods in the southern French Alps
T. Turkington1, J. Ettema1, C. J. van Westen1, and K. Breinl2 1University of Twente, Enschede, the Netherlands
2Paris-Lodron University of Salzburg, Salzburg, Austria
Abstract. Debris flows and flash floods are often preceded by intense, convective rainfall. The establishment of reliable rainfall thresholds is an important component for quantitative hazard and risk assessment, and for the development of an early warning system. Traditional empirical thresholds based on peak intensity, duration and antecedent rainfall can be difficult to verify due to the localized character of the rainfall and the absence of weather radar or sufficiently dense rain gauge networks in mountainous regions. However, convective rainfall can be strongly linked to regional atmospheric patterns and profiles. There is potential to employ this in empirical threshold analysis.

This work develops a methodology to determine robust thresholds for flash floods and debris flows utilizing regional atmospheric conditions derived from ECMWF ERA-Interim reanalysis data, comparing the results with rain-gauge-derived thresholds. The method includes selecting the appropriate atmospheric indicators, categorizing the potential thresholds, determining and testing the thresholds. The method is tested in the Ubaye Valley in the southern French Alps (548 km2), which is known to have localized convection triggered debris flows and flash floods. This paper shows that instability of the atmosphere and specific humidity at 700 hPa are the most important atmospheric indicators for debris flows and flash floods in the study area. Furthermore, this paper demonstrates that atmospheric reanalysis data are an important asset, and could replace rainfall measurements in empirical exceedance thresholds for debris flows and flash floods.


Citation: Turkington, T., Ettema, J., van Westen, C. J., and Breinl, K.: Empirical atmospheric thresholds for debris flows and flash floods in the southern French Alps, Nat. Hazards Earth Syst. Sci., 14, 1517-1530, doi:10.5194/nhess-14-1517-2014, 2014.
Publications Copernicus
Download
Share