Winter watering coefficients


Here in Oklahoma the daily ET for dormant bermuda is 0.02 inch per day. How does Rachio take into account the much lower landscape water requirement during the winter? I believe fescue daily ET is 0.06 inch per day here. Obviously these are averages.


You have to adjust that per zone. I set mine up per the defaults, but had to drop it down substantially to keep it from watering more than I need to. I am in a semi-arid high altitude environment, and the grass can survive to the level I like at much lower water levels then is suggested, even by Colorado State University.


Rainfall affects ET, but rainfall is not in the Penman Monteith Equation. Solar radiation, temperature, wind speed and relative humidity are used to calculate evapotranspiration. Many people have a hard time understanding that rainfall amounts are not in the formula. I have set through many irrigation seminars where speakers confirmed this. Oklahoma City covers a 620 square mile area and the ET has minimal variation from one part of town to another.


I don’t know exactly the details you are referring, but I know for sure that I got 1" of rain the other day, and my zones updated to show 110% (which is the upper limit, although that much rain is significant here).

Adjusting my zone’s crop coefficient made a huge impact, though I am sure there is a more technically accurate way to do it. The biggest factor where I am is getting accurate precipitation data. It varies substantially over a few sq. miles.


Download the Irrigation Associaton’s Best Management practices which goes into great detail about ET and landscape coefficients. This document took years to develop by some of the greatest:


That’s an interesting document, but it’s really getting into the weeds on a lot of things people with a current system won’t care about.

Perhaps you will find this of interest.

CSU has a lot of good information people here in the West really care about, as water here is Expensive, compared to the bulk of the country.


@eckirchn Fun fact. That article was seminal for building our flex daily schedule type and we worked with Dr. Chavez at CSU on the implementation :wink:



There is sooo much good material hosted by @franz, that’s good to know. It’s my first source for anything landscape related, but living in Colorado, it’s a must to learn how to live in this environment. It’s a tough environment to fight nature, best to just work with nature.


Yeah, CSU is only an hour from our office so we love the program and proximity, plus I’m a CSU alum.



Hey, @franz! I’m a CSU Alum too!!! But I can guarantee that I graduated WAAAAAYYYYYY before you!!! :beers:


Go Rams! :smile: