What is a “water year”?

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**** Info via Environment Canada

What is a “water year”?


In Canada, many people celebrate the New Year on January 1 with champagne and confetti, but hydrologists celebrate a bit earlier! For hydrologists, the New Year begins on October 1 and ends on September 30 of the next year. The hydrologists’ New Year is also known as the “water year.” In the same way a fiscal year is different from a calendar year, a water year is offset from a calendar year and has a deep-seated scientific purpose.

Autumn leaves reflected on the Rideau River, Ontario.

The start of the water year, also called hydrological year, discharge year or flow year, differs from the calendar year to reflect the changes in average precipitation throughout a year.

The setup for next year’s hydrologic “action” takes place starting in the prior fall, not January, and precipitation that occurs toward the end of the calendar year often doesn’t impact flow in streams and rivers until the following spring. Thus, it makes more sense from a hydrologic perspective to characterize a 12-month period with its starting point in the fall.

The water year is designated by the calendar year in which it ends, so the 2022 water year started on October 1, 2021, and ended on September 30, 2022.

To learn more about the importance of our hydrologists’ work: The Water Survey of Canada.

 

 

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