The GPM Ground Validation NASA Micro Rain Radar (MRR) HyMeX is a vertically pointing Doppler radar that obtained measurements of vertical velocity, drop size distribution, rainfall rate, attenuation, liquid water content, and reflectivity factor during the HYdrological cycle in Mediterranean EXperiment (HyMeX) campaign. The HYdrological cycle in Mediterranean EXperiment (HyMeX) aimed to improve the understanding, quantification and modelling of the hydrological cycle in the Mediterranean, with emphasis on the predictability and evolution of extreme weather events, inter-annual to decadal variability of the Mediterranean coupled system, and associated trends in the context of global change. Furthermore, this campaign aimed to improve observational and modelling systems, better predict extreme events, simulate the long-term water-cycle, and provide guidelines for adaptation measures. Special Observation Period 1 (SOP1), which was from September 5 to November 6, 2012, was dedicated to heavy precipitation and flash-flooding. More information about HyMeX is available at http://www.hymex.org/.