The Collaborative International Dictionary of English v.0.48:

Hydrometeorology \Hy`dro*me`te*or*ol"o*gy\, n. [Hydro-, 1 +
   meteorology.]
   That branch of meteorology which relates to, or treats of,
   water in the atmosphere, or its phenomena, as rain, clouds,
   snow, hail, storms, etc.
   [1913 Webster]