Add ETo AdjustmentMethod

[rmloeb]

Trying to follow the discussion regarding "base ETo"... Is the concept that watering times in OS would be set by the user to align with base ETo and the adjustment would increase/decrease in proportion to the ratio of actualEto/baseETo?

[Derpthemeus]

@rmloeb That is correct

[rmloeb]

Thank you. I'm trying to think this through from the perspective of an OS user. Does the reference (base) ETo for a specific location change throughout the year? For a specific location, is there a "standard" value?

I appreciate that OS needs a starting point. Zimmerman does that by establishing a "default" day, e.g., average temperature 70 degrees, average humidity 30%, and 0 precipitation and uses the variance from that default to set water level. I'm trying to understand how your ETo calculation is going to be actually be used. (We don't want something that is just as difficult as Zimmerman to understand for a practical application.)

[Derpthemeus]

The baseline ETo the user specifies should be chosen such that on a day where the ETo is equal to the baseline ETo, a scale of 100% will achieve the desired watering level. If the user changes their watering schedule with the seasons or is only watering crops for a few months, they should use the average ETo for that timespan; if they use the same watering schedule year-round, they should use the average daily ETo for a full year.

[rmloeb]

Your logic is quite sensible and the way that farmers do it (and they have equipment to actually measure ETo). If you compute it hourly, then you would need to average it for the day, as you do for temperature and humidity, presumably reaching the same result. (I'm basing this on the assumption that you are actually deriving water level for the next day, not the current day, which is consistent with my comment about ignoring whether it is currently raining..)