This calculator automates the calculation of irrigation scheduling using the formulas provided to Contra Costa Master Gardeners by the University of California.
The basis irrigation calculation formula: ((Ks x Kd x Kmc) x ETo x 60) / (DU x PR) / (365.25 / 7 / 12) / Days per Week / Starts per Day

Ks - PLANT SPECIES FACTOR - FROM WULCOLS
      "Water Use Classification of Landscape Species"
    INSTRUCTIONS
    Step 1 - Go to: http://ucanr.edu/sites/WUCOLS/
    Step 2 - Select: Plant Search Database,
    Step 3 - Select a City in your Region, use drop-down - Submit
    Step 4 - Plant Search, use Botanical or Common Name - Search
    Results:
    Very Low = 0.10
    Low = 0.30 (Range: 10% - 30%)
    Moderate = 0.60 (Range: 30% - 60%)
    High = 0.90 (Range 60% - 90%)
    Cool Season Grasses = 0.80


Kd - Plant Density:
    High = 1.3 (Range 1.1 - 1.3 (both tree and shrub cover))
    Moderate = 1.0
    Low = 0.9 ((Range: 0.5 - 0.9 (spaced plants, thinner canopy)


Kmc - Plant Microclimate:
    High = 1.4 ((Range: 1.1 - 1.4 (reflected heat, unusual wind)
    Moderate = 1.0
    Low = 0.9 ((Range: 0.5 - 0.9 (shaded, protected from wind)


ETo - Evaportranspiration Rate - from CIMIS
    http://www.cimis.water.ca.gov/Default.aspx
    Login, or create an account
    Select "SPATIAL" on bar menu
    Select "Spacial Report" on lower bar menu
    Delete stations in "Coordinate List"
    Add address in "Address Search"
    Select "Save Coordinates" at bottom
    Create a "Spacial Report"
    Create a "Web Report", "English Units", from <"select date one month ago"> to <"select current date"> using "Coordinate List"
    Select "Run Report"
    The report will be in inches / day with a total inches / month at the bottom
    Enter the total inches / month


DU - Distribution Uniformity, also referred to as Irrigation Efficiency (IE):
    Drip = 0.90
    Bubblers = 0.85
    MP Rotators = 0.75
    Micro Spray = 0.70
    Spray Heads = 0.60


PR - Recipitation Rate:
    Actual delivery rate of the irrigation system in inches per hour


Minutes to Runoff
    from onsite observation


Gross Water Need - inches per month
=
Days per week


STARTS PER DAY


MINUTES PER START
=