Accumulations of space-borne precipitation radar observations have enabled us to study characteristics of precipitation globally and statistically. Above all, structures of extreme precipitation are studied to renew our conventional assumption that intense precipitation is associated with intense convection. Further studies of wide-spread heavy rainfalls in very moist season in Japan clarified the contrasts between the severe rainfalls resulted from very unstable atmospheric condition and those from very moist atmosphere. The former is related to instability in terms of Convective Available Potential Energy (CAPE), while the latter is related to Moist Available Unstable Layer (MAUL) in very moist atmospheric conditions. Therefore, increase of moisture can increase the frequency of very heavy rainfalls without increasing the atmospheric instability in a conventional sense. In this chapter, we will review a series of studies that led us to restructure the knowledge of severe storms.