Arizona Turf Water Consumption


#1

Hey, Arizonans! I was wondering how your inches of water used and Rachio settings (especially crop coefficient) line up with what’s reported at https://cals.arizona.edu/azmet/data/00prptet.htm? I’m using a crop coefficient of 0.78, root depth 6", but the inches of water suggested by Rachio in the moisture report is slightly higher than what’s given on the web site. I’m sure I could tweak settings to make things line up but am curious what others are seeing.

Sum of ET over last 7 days (June 10-16) in my Rachio report is 2.26":


Average ET over last 7 days in Phoenix Turf Report is 1.55-1.77":


What changed in flex scheduling?
ET consistently above local reports
#2

I just realized the Phoenix Area Turf Report includes some other information that can be used to derive their water use numbers (see remainder of the June 16 report below):

Multiplying 2.13 (ETos for the last 7 days) times 0.73 (acceptable crop coefficient for Bermuda), we get the 7-day average watering recommendation, 1.55". Similarly, 2.13 * 0.83 (high crop coefficient) = 1.77", which also matches the report.

We can solve for the analogous ETos Rachio must have used from June 10-16. Since I entered a crop coefficient of 0.78, this implies Rachio must have used 2.26" / 0.78 = 2.90, which seems rather high. For June 16, it would have been 0.33" / 0.78 = 0.42, which is higher than all of the areas given in the turf report. I’m not sure how Rachio is coming up with ETos from the weather reports (KIWA or KCHD), but it seems like the method used must be different than what was done in the Phoenix Area Turf Report.


#3

I’ve never really used the site before so I may be interpreting it wrong, just glanced at it, but I think I’m in Phoenix Greenway area, or I know I’m semi close to Desert Ridge.

I’m currently using a CC of 0.6 (I dropped it from 0.65 in the hopes of seeing a decrease frequency) but maybe I’ll bump it up to the 0.73 as recommend on the site…and I water to 8" depth.

Greenway post 1.46" for 7 day AC. My flex daily puts down .48 each run, so the 7 days is 1.44, which is almost exact.

My cumulative ET for the 7 days is 1.62. Not really what more I can do with that information but I’d thought I’d present it to ya


#4

Thanks, @Modawg2k for taking the time. I was sort of surprised that they were recommending a Kc of 0.73-0.83. If we look at your Rachio-calculated ET value of 1.62" and your Kc of 0.6, this implies Rachio would have given you 1.62/0.6*0.73 = 1.97" for your “acceptable quality turf ET”, which is significantly higher than the 1.46" listed in the table for Greenway AC turf inches. So I think we’d be seeing the same thing if you were using a higher Kc.


#5

I plugged in 0.73 and 0.83 into my schedule and as expected there is a big increase in number of waterings. The 0.83 is just crazy talk


#6

I think I may know what’s going on. AZMET may approach the Penman-Monteith ET calculations differently than Rachio. I read in another Rachio thread that they base their ET calculations on http://www.kimberly.uidaho.edu/water/fao56/fao56.pdf. AZMET uses a version of Penman-Monteith described in https://cals.arizona.edu/azmet/et2.htm, and they also use hourly weather inputs. I’m not sure Rachio uses hourly wind inputs, which would make a big difference.

Maybe tomorrow someone from @rachiosupport can tell us whether Rachio uses hourly weather inputs for ET calculations or average weather inputs for the entire day. If it’s the latter, I can see how AZMET might get a more accurate ET number. If Rachio started with the same reference ET as AZMET, then your watering schedules would probably look about like they do now with your 0.6 Kc even if you used 0.73 Kc or higher.


#7

@mckynzee or @Support, any thoughts on why the Rachio ET values are consistently higher than the Phoenix Turf Report from AZMET? Does my theory hold water? (Awful pun, sorry.)


#8

Interesting info. @ldslaron. I’m following this thread to learn more. FWIW, my ET is set to 0.7. I was waiting for my Bermuda to come in after dethatching before lowering it to somewhere around 0.65. I’m using a 9" root depth as it worked well for me last year, so I’m putting down more water than you.


#9

Cross linking threads, I observe a similar issue in Colorado, thread here: ET consistently above local reports

I’ve got my modeled daily ET in the same range as the local turf report (I would never expect it to match perfectly because I am not using the same weather station) but to do this, I had to dial my Rachio crop ET setting down to 0.6, while the local turf report clearly states they are using an ET of ~0.8, so there is a discrepancy somewhere, and it would be nice to figure out what.