Decide when to irrigate and how long to run the system
This calculator uses the American Society of Civil Engineers (ASCE) Standardized Penman-Monteith equation for a grass reference surface (ETo) and rainfall from the selected CIMIS weather station, Open-Meteo forecast ETo and rainfall, and FAO-56 2025 edition default crop coefficient (Kc) values to calculate the crop’s daily water requirements. It then applies the FAO-56 daily soil-water-balance approach to track root-zone soil water depletion, account for crop water use, effective rainfall, and irrigation applications, and estimate when irrigation is needed and how much water should be applied.
Getting started and daily irrigation management
First-time setup: Open Advanced setup at the bottom of this page, create a crop block, and enter a block name, soil, Kc, irrigation system, and other required information. You can set up multiple irrigation blocks.
Routine use: Select a saved crop block, then follow the sections to review the irrigation recommendation, check weather data, record irrigation events, manage the Target MAD schedule, and review daily and seasonal results. For blocks using CIMIS, observed weather and the available forecast update automatically when the block opens. Each crop block keeps its own setup and season records in this browser.
Crop blocks
Select a block to continue its saved season record.
Each block keeps separate setup, Target MAD entries, irrigation events, rainfall corrections, soil-water measurements, and weather history.
Farm & Irrigation Data
Choose how your records are saved
Choose how you want your farm and irrigation records saved on this computer.
1. Irrigation recommendation
Block: Crop Block
Review the current irrigation decision. For blocks using CIMIS, weather refreshes automatically when the block opens and the refreshed weather becomes available. Wait for the automatic weather update to finish before using this recommendation.
The FAO-56 p threshold determines when modeled crop water stress begins reducing actual crop ET. Target MAD determines when irrigation is recommended. If Target MAD is greater than p, modeled crop water stress may begin before the irrigation trigger is reached.
Decision
The calculator’s current irrigation recommendation based on projected end-of-day root-zone depletion compared with today’s Target MAD irrigation trigger.Monitor
Projected end-of-day depletion on 10-28-2026 is comfortably below the Target MAD depletion. Continue monitoring.
Decision guide: Green = Monitor, Amber = Irrigate soon, Red = Irrigate now.
Today's soil-water thresholds
Read-only values that show today's modeled depletion relative to the crop-stress and irrigation-management thresholds.
Current depletion is the estimated end-of-day deficit from field capacity. FAO-56 RAW is the modeled crop-stress threshold. Target MAD is the management threshold used to trigger an irrigation recommendation.
Current root-zone water depletion
Current depletion is the estimated amount of water missing from the wetted root zone compared with field capacity. TAW (Total Available Water) is the total modeled plant-available water (PAW) stored in the wetted root zone between field capacity and permanent wilting point. When current depletion equals TAW/PAW, all modeled plant-available water in the wetted root zone has been depleted.Crop water-stress threshold — FAO-56 RAW
The root-zone depletion at which FAO-56 estimates that limited soil moisture begins reducing crop water use. RAW = p × TAW. Today's p is 44%. Below this threshold, no water stress is modeled and Ks remains 1. Above it, Ks decreases and reduces actual crop ET.Irrigation-management trigger — Target MAD
The grower-selected root-zone depletion that triggers an irrigation recommendation. It is separate from the FAO-56 crop water-stress threshold. Target MAD depletion = Target MAD% × TAW. Today's Target MAD is 40% of TAW.Irrigation-management status
Shows whether current root-zone depletion has reached today’s Target MAD irrigation trigger. It also reports when the FAO-56 crop water-stress threshold has been reached before the management trigger.Projected end-of-day depletion relative to Target MAD
31%
Recommended gross application
Not triggered
Recommended runtime
Not triggered
Recommended gallons per tree
Not triggered
Today's scheduled runtime
0 hr
2. Weather
For blocks using CIMIS, observed weather and the 7-day Open-Meteo forecast refresh automatically when the block opens.
Use the refresh button only when you want to update again during the same session, or use manual ETo and rainfall when needed.
3. Target MAD to schedule irrigation
Review or set the desired soil-water depletion threshold used to trigger an irrigation recommendation. A dated Target MAD applies from its effective date forward.
Target MAD is the management depletion level used to trigger irrigation. Editing or removing a past Target MAD entry recalculates irrigation results from its effective date forward.
No Target MAD schedule entries yet. The calculator uses the Default Target MAD until a dated Target MAD is added.
4. Irrigation events
After reviewing the recommendation and applicable Target MAD, record irrigation that has occurred or is planned. The calculator subtracts the net applied water from the daily soil-water balance.
Events may be entered as runtime, total gallons, or total cubic feet for the whole block. Editing or removing a past event recalculates the water balance from the affected date forward.
No irrigation events have been entered yet.
5. Daily schedule
The Daily Schedule summarizes the weather, crop water use, irrigation, and soil water calculations for each day. If available, enter the day's volumetric soil-water content or rainfall in the applicable box. The entered volumetric soil water content replaces the calculated soil water content and updates the calculated soil-water balance from that date forward, while entered rainfall replaces the weather-source (e.g., CIMIS) rainfall for that date.
Decision guide: Green means monitor, amber means irrigate soon, and red means irrigate now. In manual weather mode, ETo is editable and local rainfall can be entered for any date. The 14-day view is the default operational window; the 30-day view adds recent tracked history while keeping the current date and available forecast in view.
| DateThe calendar date and the crop-growth stage used for that day’s calculation. | EToReference evapotranspiration - the standardized reference ET from a well-watered short reference crop (i.e., clipped grass). | KsWater stress coefficient [0–1] that reduces the value of the crop coefficient when soil moisture is limited, ranging from 1 for no water stress to 0 for full shutdown of crop ET. | KcCrop coefficient for calculating crop ET under standard conditions. For tree/perennial blocks, the displayed final Kc includes the selected orchard-age percentage and any enabled climatic adjustment. | ETcCrop evapotranspiration under standard conditions - the ET from crops grown under standard conditions and achieving full production for the given climatic conditions (ETc = ETo × Kc). | ETc actActual crop evapotranspiration - the ET that occurs under actual environmental and management conditions (ETc act = ETo × Ks × Kc). | Target % MADThe selected percentage of Total Available Water that may be depleted before irrigation is recommended. It is the grower’s irrigation trigger threshold. | RainThe measured, forecast, or manually entered total rainfall for the day, in inches. The calculator applies the selected effective rainfall fraction when updating the soil-water balance. | Run timeThe total irrigation system operating time recorded for that date, in hours. | Net IrrigationThe irrigation water estimated to remain available in the root zone after accounting for application efficiency and the selected leaching requirement, expressed as inches of water. | DPDeep percolation: rainfall or irrigation water that exceeds the modeled soil-water storage capacity and drains below the usable root zone, in inches. | End depEnding soil-water depletion: the estimated amount of water needed to refill the wetted root zone to field capacity at the end of the day. A larger value means the soil is drier. | Soil water content %The estimated or measured volumetric soil-water content in the wetted root zone. If a soil moisture content is entered, it updates that day’s soil-water balance and is carried forward. | Irrigation recommendationThe daily irrigation status based on ending soil-water depletion compared with the selected Target MAD trigger: no irrigation needed, irrigate soon, or irrigate now. |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 10-28-2026 late-season | 1 | 0.83 | 0.21 | 0.21 | 40% | 0 | 0h | 0 | 0 | 0.21 | 16.8% PWP 8% · FC 18% | Monitor | |
| 10-29-2026 late-season | 1 | 0.82 | 0.21 | 0.21 | 40% | 0 | 0h | 0 | 0 | 0.41 | 15.5% PWP 8% · FC 18% | Monitor | |
| 10-30-2026 late-season | 1 | 0.82 | 0.21 | 0.21 | 40% | 0 | 0h | 0 | 0 | 0.62 | 14.3% PWP 8% · FC 18% | Irrigate soon | |
| 10-31-2026 late-season | 1 | 0.82 | 0.21 | 0.21 | 40% | 0 | 0h | 0 | 0 | 0.82 | 13.1% PWP 8% · FC 18% | Irrigate now | |
| 11-01-2026 late-season | 0.91 | 0.82 | 0.2 | 0.19 | 40% | 0 | 0h | 0 | 0 | 1.01 | 12% PWP 8% · FC 18% | Irrigate now | |
| 11-02-2026 late-season | 0.72 | 0.82 | 0.2 | 0.15 | 40% | 0 | 0h | 0 | 0 | 1.16 | 11.1% PWP 8% · FC 18% | Irrigate now | |
| 11-03-2026 late-season | 0.56 | 0.81 | 0.2 | 0.11 | 40% | 0 | 0h | 0 | 0 | 1.27 | 10.4% PWP 8% · FC 18% | Irrigate now |
10-28-2026
late-season · Manual fallback
ETo
Ks
Kc
ETc
ETc act
Target % MAD
Rain
Run time
Net Irrigation
DP
End dep.
Soil water content %
10-29-2026
late-season · Manual fallback
ETo
Ks
Kc
ETc
ETc act
Target % MAD
Rain
Run time
Net Irrigation
DP
End dep.
Soil water content %
10-30-2026
late-season · Manual fallback
ETo
Ks
Kc
ETc
ETc act
Target % MAD
Rain
Run time
Net Irrigation
DP
End dep.
Soil water content %
10-31-2026
late-season · Manual fallback
ETo
Ks
Kc
ETc
ETc act
Target % MAD
Rain
Run time
Net Irrigation
DP
End dep.
Soil water content %
11-01-2026
late-season · Manual fallback
ETo
Ks
Kc
ETc
ETc act
Target % MAD
Rain
Run time
Net Irrigation
DP
End dep.
Soil water content %
11-02-2026
late-season · Manual fallback
ETo
Ks
Kc
ETc
ETc act
Target % MAD
Rain
Run time
Net Irrigation
DP
End dep.
Soil water content %
11-03-2026
late-season · Manual fallback
ETo
Ks
Kc
ETc
ETc act
Target % MAD
Rain
Run time
Net Irrigation
DP
End dep.
Soil water content %
How to read the daily schedule
Dates follow California civil time; CIMIS observations remain assigned to the PST-based dates reported by CIMIS. ETc = ETo × Kc. Ks uses the FAO-56 readily available water stress threshold, which is separate from the grower-selected Target MAD irrigation trigger.
Rain is the rainfall used by the calculator; a local entry overrides weather-source rainfall for that date. DP means deep percolation in inches. A measured VWC resets ending depletion for that date and carries the corrected wetted-zone depletion forward.
6. Weekly summary
Daily ETo, ETc, actual ETc, total rainfall, effective rainfall, net irrigation, deep percolation, irrigation runtime, and ending depletion are summed into weekly values for the dates shown in the daily schedule.
Use the weekly summary to compare water demand, rainfall, and irrigation across the calculation period.
| Week | ETo (in) | ETc (in) | ETc act (in) | Rain (in) | Eff. rain (in) | Net irr. (in) | DP (in) | Runtime | Ending depletion (in) | Highest status during week |
|---|---|---|---|---|---|---|---|---|---|---|
| 10-28-2026 to 11-03-2026 (7 days) | 1.75 | 1.44 | 1.27 | 0 | 0 | 0 | 0 | 0 hr | 1.27 | Irrigate now |
7. Season trends
See how crop water demand, water consumption, irrigation application, rainfall, and root-zone depletion have changed since tracking started.
The season graphs can be printed or exported and include records from the date the block was first set up in the calculator.
Weekly Water Demand and Water Supplied
Three bars show potential ETc, net irrigation applied, and effective rainfall. The line shows ETc act after modeled water-stress effects so the weekly water balance can be interpreted consistently.
Root-Zone Depletion versus Target MAD
Daily modeled root-zone depletion compared with the Target MAD trigger, estimated RAW stress threshold, and routine wetted-zone TAW. Irrigation-event dates are marked along the bottom.
Cumulative Seasonal Water
Season-to-date cumulative ETc, actual ETc after modeled water-stress effects, and retained water supply as net irrigation plus effective rainfall minus modeled deep percolation.
8. Season summary
Cumulative water use and irrigation records for Crop Block from the date this block started being tracked through 10-28-2026.
For CIMIS blocks, completed-day observations are refreshed from the tracking start date forward. If CIMIS reports a missing ETo or rainfall value, the calculator uses the manual fallback for that measurement and flags it in the daily table and CSV.
Tracking started
10-28-2026
Set automatically when this block was first created or its saved history was reset.
Gross irrigation applied
0 in
Net irrigation applied
0 in
Full crop water requirement (ETc)
0.21 in
Actual crop ET (ETc act)
0.21 in
Rainfall
0 in
Effective rainfall
0 in
Deep percolation
0 in
Irrigation runtime
0 hr
The 14-day or optional 30-day Daily Schedule controls only how many daily records it displays; it does not affect Season Trends or Season Summary. Season results include records from the block’s tracking start date through the current date. Each block keeps its own irrigation events, Target MAD changes, weather records, and local field soil-water measurements and rainfall (if entered). The calculator does not estimate a water balance for dates before tracking started. For blocks using CIMIS weather data, completed-day ETo and rainfall are refreshed automatically from the tracking start date forward.
Advanced setup: block, soil, and Kc settingsAlmond (Prunus dulcis) setup ready
These settings are usually entered once for a block.
If you change a Block setup value after tracking has started, the calculator asks for confirmation before applying the change to the entire tracked season and recalculating past and current results.
Block setup
Enter a unique block name, tracking start date, and other field information, including acreage, crop type and other crop information, irrigation system, and soil field capacity and permanent wilting point.
The tracking start date establishes when the seasonal water balance begins. Changes to the tracking start date can recalculate the tracked season.
Farm and irrigation data are saved automatically according to your storage preference.
Tracking start date
The tracking start date is the first day included in the seasonal water-balance calculation. If you change this date during the growing season, the calculator recalculates the water balance from the new start date through today.
For blocks using CIMIS weather stations, the calculator automatically retrieves available weather data, beginning with the selected tracking start date. If you move the tracking start date forward, earlier saved records are kept but are not included in the water-balance calculations. Moving the date back again will include those earlier records.
Enter the total planted area of this irrigation block, in acres. The calculator uses this area to convert whole-block irrigation volumes entered in gallons or cubic feet into an applied water depth.
FAO-56 crop selection
Tree, perennial, and vegetable crops use the same crop-selection workflow.
Select a crop and the applicable FAO-56 crop profile or condition. Selecting another profile reloads that profile's tabulated Kc and p defaults. Tree and perennial root depth remain grower input where the FAO-56 table provides no value.
Source records: Kc Table 6.3; p Table 8.3. Tree/perennial root depth remains a grower input where FAO Table 6.3 provides no value.
Orchard age adjustment
The selected percentage is applied to the final daily Kc, after any FAO climatic adjustment. ETc is then calculated from the age-adjusted Kc.
The percentage of the crop root-zone area wetted during a routine irrigation.
The estimated percentage of the field containing enough active roots to use water stored by rainfall. It must be at least the routine wetted area.
Use 100% only when roots can use rainfall stored across the full field. For widely spaced orchards, enter a conservative estimate based on the width occupied by active roots.
Leaching requirement: Leaching requirement is applied in addition to irrigation efficiency in the net-water calculation. Do not enter leaching losses again inside the efficiency value.
Target MAD and crop-water stress: FAO-56 p and Target MAD serve different purposes. The FAO-56 p value determines when modeled crop water stress begins and may reduce actual crop ET through the stress coefficient (Ks). Target MAD is the grower-selected soil-water depletion level used to trigger an irrigation recommendation. Changing Target MAD does not change the FAO-56 crop-stress calculation. If Target MAD is greater than p, modeled crop water stress may begin before irrigation is recommended. .
Initial soil water depletion
Initial depletion is the starting soil-water deficit at the tracking start date. Choose the field measurement available at the tracking start date. The calculator converts the selected measurement to initial soil water depletion in the wetted root zone.
Three input methods are available: volumetric water content from a soil sensor, available water remaining as a percentage of total available water, and inches of water deficit per foot of soil. All three methods are converted to the same initial soil water depletion value in inches and limited to the total available water in the wetted root zone.
Soil and Kc Section
Use field-specific Field Capacity (FC) and Permanent Wilting Point (PWP) when available.
Available water capacity (AWC) is the difference between field capacity (FC) and permanent wilting point (PWP): AWC = FC − PWP (inches of water per inch of soil). Total available water (TAW) is calculated by multiplying AWC by the effective root-zone depth. For microirrigation, the calculator also accounts for the fraction of the root zone wetted by the irrigation system.
Crop stages
Calendar dates establish the crop stages. However, crop stages can also be updated using an available FAO GDD profile or crop-appearance observations provided by the user.
The calculator uses the 2020–2025 daily CIMIS RHmin and wind climatology for the selected station. Missing historical observations were filled from geographically nearby CIMIS stations before the daily climatological averages were calculated.
Selected FAO record: Almond (Prunus dulcis) · High (low vigour), vase; > 200 pl ha-1
Tabulated values: Kc ini 0.45 · Kc mid 1 · Kc end 0.75 · p 45%.
Climate-adjusted daily Kc and ETc are recalculated automatically. Custom edits remain available, but selecting another FAO profile reloads that profile’s tabulated defaults.
Effective rainfall: Effective rainfall fraction is the portion of measured rainfall assumed to be stored in the crop’s root zone and available for crop use. Effective rainfall first refills depletion in the routine irrigation-wetted root zone.
Additional rainfall can be retained as carryover water in the rest of the full root-zone profile, up to its available storage capacity. Only rainfall beyond both capacities is reported as deep percolation.
Soil texture reference table
This table is informational only. Use field-specific soil test values when available.
The table provides typical field capacity, permanent wilting point, and available water capacity values for reference; it does not replace measured field values.
| Soil texture | FC | PWP | AWC (in/ft) |
|---|---|---|---|
| Sand | 0.09 | 0.04 | 0.6 |
| Loamy sand | 0.12 | 0.05 | 0.84 |
| Sandy loam | 0.18 | 0.08 | 1.2 |
| Loam | 0.27 | 0.12 | 1.8 |
| Silt loam | 0.31 | 0.14 | 2.04 |
| Clay loam | 0.36 | 0.2 | 1.92 |
| Clay | 0.4 | 0.25 | 1.8 |
Learn more
Supporting irrigation scheduling resources
Check these public extension and industry resources for additional information.
Use these links as supporting references alongside field measurements, local extension guidance, and the calculator's documented assumptions.