This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 霳 is uncertain. It combines 雨 (rain) with 隆, but the original semantic and phonetic roles are unclear.
With 雨 (rain) above and 隆 (prosperity, high) below, imagine a heavy rain that makes rivers rise and brings abundance, though the true meaning is uncertain.
For リュウ, picture a dragon (竜, りゅう) soaring high in the rain: 竜 -> リュウ, and the rain 雨 pours down on the prosperous land 隆.