When to Start Irrigating

Delaying the initial irrigation of a season is a very effective method of water conservation. However, vines are very susceptible to water stress early season and leaf water potential must be monitored frequently to effectively schedule the initial irrigation in a season 

Using Evapotranspiration Data to Determine Irrigation Time

Historical evapotranspiration data from CIMIS (California Irrigation Management Information System) stations may be used to approximate vine water demand over a given time period.  This page describes how to calculate the number of hours to irrigate, based on historical or predicted evapotranspiration values.

Historical evapotranspiration (ET) data may be combined with current-year data to provide a very accurate model of vine water demand.  A Microsoft Excel irrigation scheduling worksheet is available to determine the number of hours per week to irrigate a vineyard based on current and historical ET data, deficit irrigation strategy, stored soil moisture and in-season rainfall.  Irrigation times are estimated using historical ET data, and adjusted using current-year ET data and the actual ammount of water applied from the previous week.

This publication by UC Irrigation and Water Management Specialist Terry Prichard et. al. describes the many variables to be considered when scheduling winegrape irrigations.

Drip System Evaluation - Emission Uniformity Determination
Quick Links:
1. How to measure the flow rate of drip emitters: collect the data
2. What to do with the data: Download the bilingual Emission Uniformity Calculator Excel Worksheet to your computer and calculate the emission uniformity of the irrigation system. Macros must be enabled when the file is opened.
3. What to do after you have calculated your Emission Uniformity

How to Sample Emitters

Each drip emitter in a vineyard discharges water at a different rate due to manufacturing variation between emitters, pressure differences in the system, and emitter clogging. This variation within a drip system causes some areas to be over-watered and others to be under-watered.  Emitters throughout a vineyard irrigation block are sampled, and that data is used to calculate emission uniformity.

How to Calculate Emission Uniformity and Adjust Irrigation Requirements

Emission uniformity is a measure of emitter variability and is used to adjust irrigation requirements and ensure the majority of vines receive the desired quantity of water. Emission uniformity values also indicate if repairs are needed to an irrigation system.  This page describes how to calculate emission uniformity after the actual discharge of emitters in the vineyard has been sampled.

To simplify calculation of emission uniformity, a bilingual emission uniformity Microsoft Excel worksheet is available. Discharge from emitters throughout the vineyard is sampled and values are entered into the worksheet for automatic calculation.

Weather and Climate Data

California Irrigation Management Information System (CIMIS)

CIMIS is operated by the Office of Water Use Efficiency and provides daily reference evapotranspiration from over 120 automatic stations throughout California

University of California maintains a database of historical data from both CIMIS stations, and from NOAA climate stations. Evapotranspiration data is only available stations ending in .A (CIMIS stations), and stations ending in .C provide only climate data.