A flood was a weather hazard which caused water to cover a land area. This could be caused by excessive rain.
In 2365, Liko's wife was among the six Mintakans (including four children) that died in a winter flood on Mintaka III. In 2366, after experiencing a storm, he feared that the Overseer would cause floods as well. (TNG: "Who Watches The Watchers")
During the Reckoning in 2374, an instability in the Bajoran wormhole caused floods on Bajor. (DS9: "The Reckoning")
Later that year, Vedek Solis was arrested by Odo for fundraising for Bajoran flood victims without a license on Deep Space 9's Promenade. (DS9: "Tears of the Prophets")