CSF Water Deficit Calculator

© Cornell University, 2016. Credits: Tool Developed by Art DeGaetano & Brian Belcher.

 The CSF Water Deficit Calculator estimates soil water content within a crop’s effective root zone to inform decision makers about current and forecasted water deficits. This information is used by farmers and irrigation system managers to determine the optimum frequency and duration of watering that is necessary to avoid plant stress.

Please also take our brief survey to give us feedback on the Water Deficit Calculator tool.

  1. How do I use this tool?
    1. Select your location by inputting your county, state, zip code, or address after clicking on the “Change Location” field, or by navigating to your desired spot on the pop-up map, after clicking “save and select location”
    2. Use the control panel on the left to input your soil type
    3. Use the control panel on the left to input your crop type
  2. 4. Use the control panel on the left to provide your planting date (for annuals) or ‘greenup’ date (for perennials, when initiation of new leaves occurs).
  3. 5. Use the control panel on the left to provide your last irrigation date, if applicable – the graph will automatically update depending on your choice for every parameter.
    6. Once all your information is chosen, view the graph output
    7. Toggle between the tabs of “water deficit results” and “next 30 days” to view charts, and toggle the “view since irrigation” checkbox to change the amount of data displayed.

Any irrigation amount above field capacity includes some water that is lost to drainage and not used by the plant. Therefore, irrigating to field capacity is done with water conservation in mind, especially for coarse sandy soils where drainage of any water above field capacity occurs over just a few hours. Providing your last irrigation date will produce graphs in two different tabs on the right. The first tab shows calculated water deficit since the most recent day water content was observed at field capacity, along with forecasted water deficit for the subsequent 3-day period. The second tab provides historical probabilities of reaching specific soil water content levels over the next 30 days, given the current water deficit.

How does this tool work?
Crops respond to water deficits in predictable ways at specific, measurable levels of water stress. This tool takes advantage of these relationships to monitor and predict possible water deficit and associated plant stress.

Many factors are at play in creating a proper irrigation schedule. This tool uses the following information to estimate current and forecasted water deficits:
Historical climatological data
Forecasted rainfall and evapotranspiration
Site-specific data that you provide about your farm, including soil type, crop type, planting dates and previous irrigation dates.

With this information, water balance calculations are performed for a soil depth of one foot (the assumed effective root zone of your crop). Precipitation, evapotranspiration, surface runoff and drainage from the root zone are all used to estimate soil water content on a daily basis. Soil water content is then compared to the soil’s field capacity to calculate the water deficit for your location. Here, the water deficit is defined as the amount of water necessary to raise the soil water content to field capacity. Color-coding of water deficits reflect the stress that plants may be experiencing at the given deficit amounts. Daily forecasted data are also used to forecast water deficits over subsequent days in a similar manner for planning purposes.

Water deficit probabilities over the next 30 days are calculated from historical data (2002-present). Using the current water deficit as model initialization together with historically observed weather during similar seasons, the water balance calculations are executed on historical data to determine the probability of observing water deficit amounts over the subsequent month.

Producers can use this tool to:
Plan your water applications with a goal of minimizing plant stress while maximizing water conservation
Assess the probability of naturally reaching certain levels of soil water content over the next month.