Posted by CCP User
on 04 May 2017

Weather Stations & Evapotranspiration (E.T.) Show me the money!


Weather Stations EvapotranspirationThe benefits of using E.T. based run times and should you be doing so on your course.


By: Craig F. Zellers, Principal – Golf Irrigation Consultants

Golf Course Superintendents can be a curious and cautious group when it comes to utilizing technology. Weather stations have been in use for decades in the golf industry, so they can’t be considered “new” technology; however, many Superintendents today are hesitant to use them to their capacity. Most on site weather stations have software that is directly linked to the irrigation software. Not only can they compute the Evapotranspiration Rate (E.T.) but they use the E.T. in order to calculate individual station run times in the irrigation central.

I’m often asked by Superintendents if they should be using their weather stations for that specific purpose. Before I can answer the question, they immediately follow up by stating “I don’t trust the weather station and I know how many minutes my sprinklers need to be running. I only use the station for rain totals and general weather information. And again before I can answer they ask, “What are other Superintendents doing and what should I be doing to establish run times”? Now it’s my time to answer and it always begins with the typical two word answer that instigates a desire to grab a cold beer or more coffee, “It depends”.


I estimate that approximately 60% of golf courses with weather stations DO NOT use them to calculate run times. Some review the current E.T. for the day and manually adjust the system or program percentages. Others use them by recording the temperatures and rain fall so that they have a year to year comparison. This data comes in handy when water and power costs skyrocket due to an unusual warm summer.


My next question and the answer help me make a well informed recommendation on a course by course basis.


#1: “Are you and your customers satisfied with the daily soil moisture levels during the irrigation season? Basically – how does your golf course look and play?

If the answer is yes, then I recommend they continue to do what works for them and the golf course. No need to change that which works. Should they desire to better comprehend how E.T. based run times can help save time and costly resources, I delve into the details of the subject.


When you have programmed the irrigation central to establish run times based on E.T. the station data in the central is used to calculate run times. This means that the database must be accurate including;

  • Sprinkler type and nozzle
  • Arcs
  • Pressure
  • Spacing

All of this data are used to establish a station precipitation rate(PR). Stations with a higher (PR) will run for less time than those with lower rates. The result is part circle sprinklers will run for less time than a full circle sprinkler. This seems simple and is basic knowledge to the seasoned Superintendent. But on most courses I discover that with irrigation system and staff changes over time, this is not the case. Another question I ask is:


#2: “Does your sprinkler data in the central match the physical data on the course”? This includes sprinkler types, main nozzles, arcs, pressure and spacing.

On many course audits we see that parts and full circle sprinklers have the same run times when a manual run time is used for the programs. Typically many tee and rough programs will have a mix of part and full sprinklers, so unless somebody took the time to identify the station and percentage adjust the part circle sprinklers down, they will run for the same amount of time as a full circle. (Yes-we see this a lot). E.T. based run times makes the adjustment for you based on the precipitation rate for every station

The bottom line is that we usually run into the following scenarios on most golf courses;

  • Despite what may have been programmed in the past, every part circle sprinkler, despite arcs that range from 45-330 degrees on the course are set at 180 degrees.
  • Irrigation staff has changed nozzles and sprinklers in the field but not in the central.
    As sprinklers age, the pilot valves which control pressure out of the nozzles, become worn.
  • Large turf sprinklers were replaced with shorter range, low pressure sprinklers spaced at 20’ and not 65’. The change in the field was not made in the central.

Is your head spinning yet? Still reading? – Great! Let me show you an example of how a minor difference in data can affect a station run time. For this example, we will ignore all data used to calculate E.T. and use only the arc setting on a part circle sprinkler.

Sprinkler Type                                                                 Arc Setting in degrees              Precipitation Rate           E.T. based run time –Minutes & Seconds

Sprinkler Type - DT35 Arc - 180 Precip Rate - 1.15 Run time - 7:58
Sprinkler Type - DT35 Arc - 210 Precip Rate - 1.29 Run time - 9:17



As you can see, a minor increase in the arc results in a run time that should be 1 minute and 19 seconds longer than the same sprinkler actually set at 180 degrees. I know it does not seem like a big difference but considering the effect on conditions, it is and quite often we see arcs set at 270 or 90 and they are listed as 180 in the central.


What typically ends up happening is the area begins to dry out and the hand waterers take care of the same area day after day during the summer season. . Or the Superintendent increases the station percentage and must do so for every part circle not actually set at 180 degrees. In a reverse scenario the area is overwatered and a constant wet area exists.

When we see that much of the field data does not match the central, then running the system via E.T. is not my recommendation. A complete sprinkler inventory audit followed by programming accurate data is always recommended under this scenario.


If all of these factors and changes were correctly programmed in the database, then running the system via E.T. should prove to have rewarding results in soil / turf quality and consistency across the entire course. Hand watering will most likely decrease and there are less “fires to put out”.

“So should you be using the weather station and E.T. to calculate run times? Yes”!  And under most circumstances provided your central database is programmed with up to date field data. If the E.T. generated run times seem a little higher than you think they should be, establish a base global percentage of 80-90 or whatever gets you closest to the manual run times that you want. Irrigation software also allows the user to select a manual E.T. If a golf course does not have a weather station or it is no longer accurate and requires servicing, there are a variety of other sources where many Superintendents go to retrieve an E.T. that is similar to the actual E.T. on their property. These include;

  • CIMIS (California Irrigation Management Information System)
  • Weather Underground
  • A nearby airport or neighbor with a weather station
  • A weather station on-site that calculates E.T. but is not linked to the central irrigation software

The subject of E.T. and run times arises often. In fact, everything irrigation related is always a hot topic in our business, given the cost of water and the recent drought. It is worth mentioning one more question that I ask related to run times and water & power expense.

#3: “Is somebody adjusting run times or station percentages in the central on a daily basis”?

In addition to running off of E.T., most golf course Superintendents do not have enough time to fine tune and adjust the central on a daily basis. It is my opinion that it is easy to find at least 50 stations on a daily basis where the percentage of water could be decreased. I proved this theory correct last year while running the irrigation central for two weeks during the 2016 Women’s U.S. Open at Cordevalle G.C. On some days I adjusted down at least 80 stations and decreased the nightly irrigation gallons by 3% without a negative effect on conditions. This requires one to sit in front of the central and manually change station percentages, regardless if the weather station is used. For those paying for water and power, this seems like a minor change but think of the big picture. If your course pays a total of $400,000 annually for water and power, how much would you save if you could decrease your nightly irrigation quantity by 2%? The answer is $8,000 annually and it is not a number to be overlooked when so much pressure currently exists to decrease expenses.

In conclusion, if you have a weather station I recommend using it. If needed, complete an inventory audit and ensure that your database is programmed with up to date sprinkler information. If your efforts result in lower expenses for water and power, your value increases. If turf conditions improve and become more consistent , the value of the course goes up. If the value of the course goes up, perhaps green fees can be raised or membership increases and you may get a raise. That is the icing and the sprinkles on the cake.

For questions or comments, Craig can be reached at (415) 342-1030 or This email address is being protected from spambots. You need JavaScript enabled to view it.