The Collaborative International Dictionary
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.
Wiktionary
n. the branch of meteorology that studies the occurrence, movement and changes of state of water in the atmosphere
Wikipedia
Hydrometeorology is a branch of meteorology and hydrology that studies the transfer of water and energy between the land surface and the lower atmosphere. UNESCO has several programmes and activities in place that deal with the study of natural hazards of hydrometeorological origin and the mitigation of their effects. Among these hazards are the results of natural processes or phenomena of atmospheric, hydrological or oceanographic nature such as floods, tropical cyclones, drought and desertification. Many countries have established an operational hydrometeorological capability to assist with forecasting, warning and informing the public of these developing hazards.