I´m quite new to opensprinkler and like the idea of weather-based adjustment of watering time. Monitoring the adjustment in % during the last days of higher rainfall (approx. 30mm within 4 days) I wonder, why the ET algorithm wants to water 135% today at actual 22°C, while yesterday the adjustment was to 0% (which in my opinion was absolutely correct). The prediction for tomorrow also shows around 5mm precipation. In my opinion there is no need to water today, too, and if, never ever higher than 100%.
I use ET algorithm with the standard calibration based on my location (clicked “detect baseline ETo) with 2.8mm/day and elevation 183m.
As I don’t want to water on a daily schedule, but every ~3 days (read several articles about the grass ingraining deeper, if one doesn’t water daily), here’s my question: Do the weather-based algorithms calculate their adjustments on a daily base (using the exact last day’s precip, temp etc.) or between two schedules (e.g. averaging the adjustment needs of day1 after last executed watering, day2, … dayN)?
The ET algorithm always uses yesterday’s weather parameters (temperature, humidity, precipitation), it does not include today’s precipitation so far, so the watering percentage calculated might not look ideal but keep in mind that today’s weather parameters will be accounted into tomorrow’s watering percentage.
Whether you use ET or zimmerman algorithm, it calculates watering percentage once per day, so the number remains the same until your local time crosses midnight. It always uses yesterday’s weather parameters — I agree that using the accumulated weather parameters over the gap between two runs would be better, but that would involve a lot more changes to the weather script, and it might not always be possible (for example, if you set a program to run every 14 days, I don’t think the weather provider gives history data of that long).
This reply was modified 6 days, 13 hours ago by Ray.