You need to specify in the question what you are talking about.
Floods usually occur in florida. {I think}
they usually occur in summer
they can occur at anytime.
They usually occur in desert or places on the equator.
The chance that a given event will occur, usually expressed between the number 0 (will not occur) and 1 (will occur) is called probability.
monsoons usually occur in Asia, India, some parts of Africa, and North America
Volcanoes occur on tectonic plate boundaries
Clouds
it usually occur from september to november.
earthquakes usually occur at tectonic plate boundaries
it usually occur from september to november.
Droughts in America usually occur in the summer and hot seasons