Can severe rain events over the Mediterranean region be detected through simple numerical indices?
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This work evaluates two numerical warning indicators of severe weather. These indicators, the MKI and RDI indices, were developed within the framework of the EU-funded FLASH project which studies flash flood events in the Mediterranean Basin. The MKI (Modified K-Index) is a modification of the K-Index, which expresses probability of lightning activity, and the RDI (Rain Dynamical Index) is the integrated upward moisture flux. The indices were tested on 59 episodes which occurred during nine rainstorms in Israel, Greece, Spain, Italy, and Cyprus. The data for calculation of the indices included rain cell identification derived from microwave radiometer imagery of polar orbiting NOAA satellites, rain RADAR data, and lightning activity from the international ZEUS detection system. Atmospheric data with 0.5° × 0.5° spatial resolution and 6-h time resolution were used for the calculation and the display of the two indices. The indices were tested by calculating the spatially correlating locations with high index values and actual locations of intense rain and intense lightning. The RDI detected both event types: rain and lightning, with a statistically significant success rate and a low rate of false results. The MKI was successful in indicating intense lightning activity, but the rate of correct indications was not statistically significant and there was a high rate of false indications. The results suggest that the RDI computed with output of weather prediction models is a potentially good predictor of torrential rain and therefore can predict flash floods caused by such rain in the Mediterranean region.
KeywordsFlash flood Lightning activity Thermodynamic and dynamic indices Modified K-Index Dynamic rain index Mediterranean climate Extreme weather
This research was conducted in the framework of the FLASH project for which partial funding was provided, under Contract Number 036852 of the EU 6th Framework Program. The study was also supported by Grant 108/10 of the Israeli Science Foundation (ISF). We thank Dr. Vassiliki Kotroni and Dr. Kostas Lagovardous from the National Observatory of Athens for their help with the ZEUS lightning data. Special thanks go to Mrs. Judith Lempert, the linguistic editor of the text. Thanks are due to Mr. Roy Yaniv from Tel Aviv University for deriving the lightning maps.
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