NWS Western region now using USGS "Water Year" definition...

[saratogaWX]

I'd received a note from one of my website viewers saying

The National Weather Service has changed the way it tracks rain on an
annual basis, moving from a July-June calendar to an October through
September timetable.

so I fired off a question to the Western Region NWS asking

Hi,

I understood that the 'water year' for our area (SF/Monterey) was from July 1 to June 30 historically.
Has that now changed to the USGS  water year of October 1 to September 30th?
If so, was there an announcement to that effect?

and received the reply

Hi Ken,
Technically speaking, the water year has never been July 1 to June 30...up until last year, the our NWS office and a few others were misrepresenting the July 1 - June 30 time frame as the water year.  There is a bit of mystery as to where this date range (July 1 - June 30) came from, as the Oct 1 - Sept 30 Water Year is used by all hydrologists and most meteorologists in the Northern Hemisphere.  To reflect general usage of the term "water year" we adjusted/adapted our date range to Oct 1 - Sept 30 when referring to the Water Year, to be consistent with the USGS, CA DWR, and elsewhere.  We made the change, along with CA NWS offices, and numerous announcements were made (although I wasn't involved with those announcements, so can't point you to specifics).

For the "big picture" here, the date designation is somewhat arbitrary, as the intent with both date ranges is to capture our Mediterranean-like wet season.  You could just as easily start August 1 if you really wanted to.  We are just appropriately falling in line with the rest of the hydrology and meteorology community, especially when we utter the phrase "Water Year".  The statistics change a little, but not much.

Let me know if you have any additional questions.

Mark

I must have missed the announcement (and couldn't find it in a search on the NWS sites).

Anyway, the entire nation is now using the Northern Hemisphere convention of October 1st-September 30th for the Water Year and now matches the USGS hydrology measurement period. 

I've changed the rain detail page on my site to have an October start for the year's details.

Best regards,
Ken

[elagache]

Dear Ken and WeatherCat drought watchers, . . .

I must have missed the announcement (and couldn't find it in a search on the NWS sites).

Anyway, the entire nation is now using the Northern Hemisphere convention of October 1st-September 30th for the Water Year and now matches the USGS hydrology measurement period. 

Huh? . . . .

Sure, in places where summer rains count as part of the hydrological budget, I suppose that makes sense.  However in California (especially northern California) the effect of the monsoon has been traditionally negligible.  On the other hand, we have gotten early winter storms in September.  To count rain that falls in September as part of the water year when the last rains may have fallen in June (if you are lucky . . . ) . . . . That is just plain silly.

Sounds to me like there was a bureaucracy squabble and the real science that should be considered when defining such things - wasn't!. . . 

Sigh, . . . . . Edouard  

P.S. I'm not changing the way I count the water year on my personal weather web site!

[Steve]

CoCoRaHS has also used the October 1-Septenber 30 since at least 2006. (Not when they started, just as far back as I could find a reference.)

[elagache]

Dear Steve and WeatherCat rainfall monitors, . .

CoCoRaHS has also used the October 1-Septenber 30 since at least 2006. (Not when they started, just as far back as I could find a reference.)

Unfortunately this is further evidence of the "one size fits all" mentality that should not apply in this case.  A October 1-September 30 makes good sense in a lot of places.  Even the deserts of the southwest get a lot of rain in the summer - so for most of the country this makes sense.  Is it better to force California to use a standard that scientifically doesn't make any sense for it just to make it easier for bean-counters?

Proper scientific understanding should always have priority over bureaucratic convenience.

Oh well, . . . . Edouard