Certified Landscape Irrigation Auditor

What is the definition of effective rainfall?

1. The rain that contributes to runoff

2. The total rain actually stored in the root zone

3. The rain that evaporates before reaching the soil

4. The measured rainfall over a given period

The correct answer is: The total rain actually stored in the root zone

The definition of effective rainfall is centered around the amount of rainfall that is actually available for plant uptake and contributes to soil moisture within the root zone. This means it is the portion of rainfall that infiltrates the soil and becomes available for plants, as opposed to rainfall that runs off the surface or evaporates. Effective rainfall takes into account various factors such as soil type, vegetation cover, and climate conditions, which all influence how much of the total rainfall makes its way into the root zone. It emphasizes that not all rainfall is effectively utilized by the plants, as some may be lost through runoff or evaporation before it can be absorbed by the soil. Each of the other choices highlights aspects of rainfall but does not align with the definition of effective rainfall. For example, rainfall that contributes to runoff does not aid in plant growth since it does not infiltrate the soil. Similarly, rainfall that evaporates before reaching the soil is also not available for use by plants. Finally, the total measured rainfall over a specified period includes both the effective and non-effective components, making it a broader measurement that does not specify availability to plants.