Weather patterns (including amount of rainfall), plant type, and irrigation system efficiency (a measure of how evenly the irrigation system applies water), are all taken into account when determining how much water the irrigation system needs to apply to keep the landscape healthy. This is known as the irrigation requirement.
The historical irrigation requirement from 2003 to 2008 in the Denver-area was 18 gallons per square foot (GPSF). Years with an irrigation requirement above the historical average of 18 GPSF indicates a hotter, drier year (represented as greater than 100 percent) and years with an irrigation requirement below the historical average indicates a cooler, wetter year (represented as less than 100 percent).
To determine the irrigation requirement for bluegrass in the Denver-area, the following information is used:
- Local weather stations to collect weather data, including rainfall
- An irrigation system efficiency of 75 percent, which is considered efficient by industry standards
- An irrigation season of April 15 through Oct. 15
This chart will be updated on a regular basis throughout the irrigation season.
The daily weather data collected includes temperature, relative humidity, wind speed, rainfall and evapotranspiration (ET).
Evapotranspiration is the combination of two separate processes whereby water is lost from the soil surface, through either evaporation or usage by plants (transpiration). Evaporation and transpiration occur simultaneously. They are measured here in inches of water per day.
ET is calculated by measuring the energy from various sources that impact plant growth. These energy sources are wind, air temperature and humidity.
Relative humidity compares the actual amount of moisture in the air to the greatest possible amount that could be in the air (100 percent) at the same temperature and pressure.
Historical Weather Data
If a month is not linked, then no data is available for that period. Some months may have only partial data.
|Rocky Mountain Metropolitan Airport|
|Denver International Airport|
|Buckley Air Force Base|
|Front Range Airport|
Where is data collected?
Denver Water provides weather data from the National Weather Service on a daily basis from five airports situated in the metro area: Rocky Mountain Metropolitan Airport (B), Denver International Airport (C), Centennial Airport (D), Buckley Air Force Base (E) and Front Range Airport (F).
The red shaded area denotes Denver Water’s service area.