ירמיהו מט:ד פירוש: רש״י

You boast Heb. תתהללי (vanter in French).

about the valleys? That your land is a land of valleys and lack of rainfall is not harmful to it since the sun does not penetrate into it.

Your valley is flowing A misfortune of an overabundance of rain shall come upon it until the water will flow in the valley and inundate the roots of the grain So did Menahem [Machbereth Menahem p. 77] explain it.