## Calculating your landscape's evapotranspiration, ET_{L}

Once you determine the local reference evapotranspiration rate (ET_{0}) and the appropriate plant adjustment factor or factors (K_{L}) for your landscape, you can calculate the site's rate of evapotranspiration (ET_{L}).

To do so, just use the equation mentioned earlier:

- A landscape plant's rate of evapotranspiration is equal to the local reference evapotranspiration multiplied by the appropriate plant adjustment factor
- Or, expressed with symbols: ET
_{L} = ET_{0} × K_{L}

It is important to note that, in many cases, there will be a different landscape adjustment factor for each irrigation zone.

### Example:

You want to estimate the rate of evapotranspiration of a mixed planting of holly oak, Twin Peaks coyote brush, and trailing lantana in a park in Los Angeles:

- By referring to the relevant tables, you find that the species factors for all three have been determined to be 0.2. Consequently, you assign a species factor of 0.2.
- Since the planting is full, making for a canopy cover of 100%, and there are three types of plants — a tree, a shrub, and a ground cover, you assign a high density factor of 1.2.
- The planting is exposed all day to the sun and not exposed to any unusual amount of wind, so you assign an average microclimate factor of 1.0.
- Multiplying the species factor 0.2 by the density factor of 1.2 by the microclimate factor of 1.0, you arrive at a landscape adjustment factor of 0.24.
- You find the normal-year average reference evapotranspiration for the month of July for Los Angeles is 6.5 inches.
- Multiplying the landscape adjustment factor of 0.24 by 6.5 inches, you arrive at a landscape evapotranspiration rate of 1.56 inches.