Water Years

Data which relates to precipitation is often summarized or aggregated based on the "Water Year". This is especially relevant in California with wet winters and dry summers.

Water Years begin in October and end in September, which is a better match with the precipitation cycle than splitting years in the middle of the rainy season.

A given numbered water year begins in October of the previous calendar year. So for example, November of water year 1960 is actually in calendar year 1959, while March of water year 1960 would be in March of calender year 1960.

So for example: