ET consistently above local reports


#1

Hello! My Rachio has been watering fairly frequently, every 3rd day or so. I was hoping to do better, and the city’s recommendation is less often & less water than what the Rachio is delivering. Additionally, the grass & soil never really “dry out”.

I noticed today that the crop ET in the Moisture Level report is fairly high. I looked up the local ET report, which is gathered from a location close by:

http://www.northernwater.org/weatherdata/228_turf.htm

Compare to the moisture level report in my Rachio:

28th: 0.25
27th: 0.33
26th: 0.24
25th: 0.15
24th: 0.14
23rd: 0.12

You can see their Kc is 0.81 for “Standard”, and my Rachio is set to 0.80. Allowed depletion is 0.50

I’m using PWS data (http://weather.gladstonefamily.net/site/search?site=AV224). It appears to be a good quality PWS, and Google Streetview shows a very tall mast, so it’s likely not mounted under the eaves! I hesitate to use the airport 8 miles away, because weather & rainfall is extremely localized around here, but maybe I should experiment.

Has anyone else had a similar experience? Are there major possible explanations for the discrepancy that I’m not thinking about?


Arizona Turf Water Consumption
#2

Hmm, and I have just noticed Rachio doesn’t seem to get wind speed from AV224, which I was reading on these boards is a significant portion of ET computation… I wonder what happens in that case?


#3

Yes, I posted in Arizona Turf Water Consumption and What Changed in Flex Scheduling, drawing similar comparisons. I’m not sure about the use of wind data on a PWS, though - I use an airport station.

Unfortunately I don’t think there is a perfectly standard method of calculating ET, so I figure YMMV. (There’s Penman-Monteith but apparently there are different ways to use it.) I’d like to hear from Rachio about the differences in methodology since I’m an engineering geek who likes numbers. :nerd: But for now maybe we just use crop coefficient as a lever to compensate.


#4

Thanks for the note! Yeah, your experience pretty much mirrors mine.

The bit about PWS & wind was a red herring- I now see Rachio just omits the wind field in the weather widget when the speed is 0.