Whats the difference between the “rainfall season” and “water year” in the West?
Meteorologists in the West commonly define the rainfall season as July 1 – June 30. This works well in most of the West due to the usual summer “drought,” making it a logical place to separate the seasons. In other parts of the USA, where a significant amount of annual precipitation falls in the form of summer thunderstorms, meteorologists simply use the calendar year. Hydrologists, who study surface and groundwater, use a “water year” that begins Oct. 1 and ends Sept. 30, which coincides with the year’s lowest stream flows. You can read more about California’s climate on this USA TODAY resource page.
