How Does ETwater Adjust For Rainfall?

In addition to making adjustments in response to changes in ET, ETwater also automatically adjusts your watering schedule when rainfall occurs.

First, rainfall data is gathered daily from a weather station near your site. ETwater then takes the gross rainfall measured at the weather station and calculates the amount of effective rainfall. Effective rainfall is the amount of rain that penetrates the soil in the plant root zone. Not all rainfall is effective. For example, a light mist measuring only 1/100th of an inch is typically not effective because no moisture penetrates the soil. Similarly, a big storm supplying several inches of rain typically generates only a percentage that is effective since much of the rain water is not absorbed into the soil due to runoff.

Once the effective rainfall is determined, ETwater will calculate the amount of moisture that has been added to the soil. If the soil is already saturated due to an earlier rainfall or irrigation event, then the added moisture from the last rain event will have no effect. If, however, the rain event increases the soil moisture level, then the next irrigation date will be postponed accordingly. For example, if the soil absorbed .5 inches of effective rainfall and the average daily ET is .1 inch, then the next irrigation date will be delayed by five days.

Since rainfall tends to occur frequently in the West and Southwest during winter months and typical watering intervals tend to be long due to low ET rates, it is not uncommon for the ETwater system to delay irrigation for many weeks or months during the winter season.

If you prefer to adjust irrigation based on rainfall at your specific site, you can add a rain sensor or tipping bucket rain gauge to your ETwater smart controller (for a modest additional cost) and your watering schedules will be automatically adjusted according to onsite rainfall.