The weather in Germany was improving a lot for the last 10 days. My OpenSprinkler DC 3.0 is working again and I have had a closer look at the OS Weather Service and especially the Zimmerman method.
The attached diagrams show the start of the garden season, beginning April 2020. Without any rainfall it is getting warmer day by day, close to daytime highs of 25°C. The garden watering is served by my reactivated OpenSprinkler system at 7:00 o’clock every 2nd day. The Weather Service determines water levels around 70% for garden watering at those first warmer spring days. The OpenSprinkler App and Firmware have been updated to the newest versions [App: 2.1.7, FW: 2.1.9(2)]. The Weather Service (Version 2.0.2) is installed on a local server (Raspberry Pi) and gets its data via WeeWX from my Netatmo Personal Weather Station. Weather adjustments are performed in accordance with the Zimmerman method using last 24 hour data to periodically update the water level.
The original Zimmerman Method has used yesterday’s temperature and humidity data together with yesterday’s and today’s precipitation data for the %Watering calculation. The “new” Zimmerman Method that comes with the Weather Service (Version 2.0.2) update uses the last 24 hours temperature, humidity and precipitation data. Its %Watering outcome is continuously recalculated! This updated Zimmerman Method gets closer to the ideal world of using forecast weather data, as it includes actual weather developments. However, the %Watering results vary during the day and are not easily comprehensible, if e.g. looking at yesterday’s and today’s reports available from Netatmo, WeeWx or Weather Underground. As expected, every midnight both calculations deliver the same %Watering result.
I hope it was worth to share this information. It maybe helps others who like to select the Zimmerman method as weather algorithm.