Recent change to Evapotranspiration data source(s)?

[RandyAZ]

Hello Rachio community! I am a long time Rachio user and avid reader of the forums (both since 2018), but this is my first post.

I was working offline with Rachio support to investigate some unexpected evapotranspiration (ETo) values reported in my Flex Daily Soil Moisture data table. Because the actual/past ETo values were higher than expected based on official sources near me, I asked which official source(s) Rachio used to calculate ETo for my specific location. I was surprised when support said that ETo values are calculated using the data from my selected weather source: Weather Network, National Weather Station, or Personal Weather Station:

“The source data for calculating ETo will always be based on the Weather Source you’ve chosen (either the Weather Network or a specific PWS). In your case, with <local_PWS_name> selected, the controller uses temperature data, elevation, latitude, time of year, and other factors from that source to calculate ETo.”

While I knew that this was true in the distant past (circa 2016), my understanding is that Rachio changed their methodology to use only “official” data sources for ETo calculations in 2018:

@franz

We don’t use PWS data for deriving ET. Tried this in the past and we saw a big gap between forecasted ET and PWS ET. I would like to get more hyper local ET at some point.

@franz

We only use nationally observed data to derive ET. We used to use forecasted data for ET and allowed PWS observed data for ET but the forecasted waterings were always widely different then observed waterings since we would use the “observed” ET from the PWS to decide if we were watering or not for that day. The biggest discrepancy was wind observed from PWS stations which was usually much lower than wind from properly setup national stations. This would have us watering about half as much as was recommended since the recorded ET from PWS stations was usually much less. There is a thread about this exact topic somewhere in the community history Went back and forth with this and the approach we’ve adopted seems to be the most predictable.

I was unsure if the response from Rachio support was announcing an official change to the ETo calculation methodology. If so, I would be interested in understanding more details. I do use a local PWS for my Rachio controller, but until now, I have not been validating all of the data that could possibly be used for ETo calculations, including wind, solar radiation, etc. (Previous posts in the forums had confirmed that PWS precipitation was the only data used for calculations.)

Can any of the forum members or Rachio staff provide more insight on this possible change?