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Vineyard Yield Water Needs Estimator

The Vineyard Yield Water Needs Estimator uses reference evapotranspiration and a crop coefficient to estimate vineyard crop water use, then subtracts effective rainfall and adjusts the remaining irrigation depth for system efficiency. It converts that gross depth into gallons for the selected acreage and number of weeks.

This approach is useful for scenario planning when local ET data and an appropriate crop coefficient are available. Vineyard water management is highly site- and growth-stage-specific, so the coefficient, effective rainfall, and irrigation efficiency should come from the best local information available rather than from a generic default.

Calculator inputs

acres
in/week
Kc
in/week
%
weeks
Result
—
total vineyard irrigation volume
Estimated crop ET—
Net irrigation depth—
Gross applied depth—

1. Enter vineyard acreage
Use the area covered by the irrigation estimate.

2. Enter reference ET
Provide the local reference evapotranspiration for the same weekly time basis shown on the page.

3. Set the crop coefficient
Use a Kc appropriate to the vineyard canopy, growth stage, and local method.

4. Enter effective rainfall
Subtract only rainfall expected to contribute useful root-zone water.

5. Set irrigation efficiency and weeks
Enter the delivery efficiency and planning duration, then review crop ET, net depth, and gross applied volume.

Crop ET (ETc) = Reference ET (ET0) × Crop coefficient (Kc)
Net irrigation depth = max(ETc − Effective rainfall, 0)
Gross irrigation depth = Net irrigation depth ÷ (Efficiency ÷ 100)
Total gallons = Gross depth × Vineyard acres × Weeks × 27,154

ET0, rainfall, and gross depth are all treated as inches per week. One acre-inch is approximately 27,154 US gallons.

What the result means

The result is the gross irrigation water volume needed to replace estimated crop ET after effective rainfall, adjusted for irrigation efficiency.

ET0 and crop coefficients vary by location, canopy development, growth stage, and method. Use local irrigation guidance when available.

Given

  • 35 acres
  • 1.6 in/week reference ET
  • 0.70 crop coefficient
  • 0.15 in/week effective rainfall
  • 90% irrigation efficiency
  • 10 weeks

Calculation
ETc = 1.6 × 0.70 = 1.12 in/week.
Net depth = 1.12 − 0.15 = 0.97 in/week.
Gross depth = 0.97 ÷ 0.90 = 1.0778 in/week.
Total gallons = 1.0778 × 35 × 10 × 27,154 ≈ 10,242,893 gal.

Result
Total vineyard irrigation volume ≈ 10.24 million gallons.

The gross applied depth is higher than net crop demand because the irrigation system is assumed to deliver 90% of applied water effectively.

Where should the crop coefficient come from?

Use a locally appropriate source or vineyard irrigation program that matches your canopy, growth stage, training system, and ET method. Kc can change during the season.

Can I enter daily ET0?

Not directly unless you first convert it to the weekly basis used by the calculator. All depth inputs should refer to the same time period.

Why is rainfall subtracted after multiplying by Kc?

Kc converts reference ET into estimated crop ET first. Effective rainfall is then treated as water that offsets part of that crop water demand.

What if effective rainfall is greater than crop ET?

Net irrigation is set to zero for that modeled week rather than becoming negative.

Is this the same as an orchard water-depth estimator?

The volume conversion is similar, but this vineyard model explicitly derives crop demand from ET0 and Kc instead of asking you to enter the target crop-water depth directly.