Lightning and rain dynamic indices as predictors for flash floods events in the Mediterranean

摘要

The FLASH EU funded project aims to observe, analyze and model lightningactivity in thunderstorms for use in short term forecasting of flash floodsin the Mediterranean region. Two new indices, aimed to assess the potentialfor heavy precipitation and flash-floods, are proposed and evaluated. Thefirst is a lightning index – the MKI, which is a modified version of theKI-index. The applied index gives more weight to the lower- and mid-levelrelative humidity. The second is a new rain index, the RDI, which is theintegrated product of specific humidity and vertical velocity. With the aimto contribute to the aforementioned objectives, 3 flash flood events, two inIsrael and one in Greece are analyzed in the present study, using the 2proposed indices.The NCEP/NCAR reanalysis database, of 2.5°×2.5° resolution,failed to resolve the meso-scale features of the observed flash floodevents. Therefore, the ECWMF database, of 0.5°×0.5°resolution, was used for calculating and displaying the two indices.Comparison between the observed rain and lightning and the respectiveindices for the two pieces of data was performed for the flash flood events.The results show good concordance of both indices with timing and spatialdistribution in 2 of them, while in one of them is displaced by more than50 km. The good agreement in locating the maximum between the MKI and RDIsuggests that the proposed indices are good predictors for both intenselightning activity and torrential rain and consequently, for potential flashfloods.