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Weather's Impact on Growing Conditions Quantified.

Weather plays a big roll in how difficult a growing season might be. Things like temperature and rainfall are completely out of our control but also have a huge impact on what is possible to achieve for golf course maintenance operations. I've looked at many different ways to quantifying how weather can help or hinder my operations and have found that it's not as easy as it might first seem. There are a few techniques that I have come across that can paint a general picture of the weather may have impacted your growing season.

I've been a big time user of the growth potential since 2012 when I first learned about how Micah Woods was using it to calculate potential fertilizer use. The growth potential is a temperature based growth model and can make a bit more sense out of temperature data and how it might impact turfgrass growth. This is because turf growth isn't directly proportional to temperature. 

At low temperatures there is little growth but once you get past a certain threshold, growth rates explode. Growth also slows as you pass a certain temperature threshold. We all know about times when it is too hot for good growth and the growth potential model does a pretty good job at expressing this concept. I especially like adding up the daily growth potentials numbers for a monthly GP SUM. As the max GP can only be 1 or 100% the max monthly GP SUM can only be 30 or 31 depending on the number of days in that month. The table below shows how our typical spring heat was delayed but extended longer into the fall.


Temperature isn't the only thing that matters for growth and more specifically, how difficult it is to achieve good playing conditions. We also need water. Water that isn't provided by mother nature requires irrigation and irrigation is harder than not irrigating.

I've looked at different ways of quantifying how difficult a year might be for irrigation. Things like precipitation, moisture deficit, ET, water usage and number of irrigation cycles required are all useful metrics in their own way, but on their own don't provide a clear picture on the impact the weather had on our ability to provide good playing conditions.

The best way I have found to express the concept of weather's impact on playing conditions is to combine both the growth potential with how often the rain provides all the water that the grass needs over a week's time. I first came across this concept from Micah Woods and the numbers that it provide are the best I have yet to come across.

The idea of what makes a good day is this. Any day where the growth potential is above 20% AND the 7 day effective rainfall is greater than the 7 day ET with a 60% crop coefficient. Essentially, it it warm enough AND wet enough for the weather to not negatively impact turf growth.

The following table is this metric calculated for my golf course. As you can see, there is quite a bit of seasonal variation from one year to the next. 2020 was the easiest growing season of my 20+ year career growing grass and we did it with only 4 staff vs our regular 10! This was because the weather helped us out. We had a warm spring and summer with timely rainfall. We only hand watered 4 days that season.

This year (2022) was a different story. We had a very cool and wet spring. We didn't get good growing temperatures until June. This was easily overcome with supplemental fertilizer applications to increase growth to match the wear and tear patterns we observed. In July it stopped raining and we were required to irrigate for 121 days in a row! Once the rains returned in the fall, it was too cool for growth. Areas that we could irrigate fared ok but areas that were beyond the reach of our sprinklers are still "dormant" from the dry summer weather.



There are, of course, many other things that go into good playing conditions, but most of those we have much more control over. I don't know about you, but I personally have no control over the weather.

This model also doesn't take into account extreme weather. In 2021 we had 2 extreme weather events that caused long term issues. A heat wave which saw temperatures rise into the mid 40's caused widespread plant death and a few disease issues. It also doesn't account for excessive rainfall although it wouldn't be hard to work that into the model. In the fall we had torrential rains that caused damage to local infrastructure we have never seen before. The course fared just fine however and it wasn't a big problem because our expectations for conditions in November are minimal. 

This model suggests it was an average year but those 2 isolated events caused a lot of hardship on our course conditions. They were brief, but also extreme.

So far, this is the best model I have found to describe the impact weather has on good growing conditions in a general sense.







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