Last summer at 36 locations
The delta GP (ΔGP) can be used as a statistic to show how difficult the summer was for cool-season grasses
For any day in the year, one can calculate the cool-season grass growth potential (GPC3) and the warm-season grass growth potential (GPC4). These growth potential functions take the average air temperature as the input and return a GP value on a scale of 0 to 1, or 0 to 100% if you prefer.
When the GPC3 is greater than the GPC4, I consider the temperatures to be more suitable for cool-season grass than for warm-season grass.1 When the GPC4 is greater than the GPC3, then temperatures seem more suitable for warm-season grass. One of the site-specific charts on the PACE Turf weather page is labeled “Growth Potential C3-C4” and that chart shows this difference, what I call delta GP (ΔGP), for each of the past five years.
I’ve applied this ΔGP calculation to temperature data from last summer for 36 locations around the world.
I actually included 40 locations initially, but Auckland, Cape Town, San Francisco, and Wellington did not make the chart, because there were 0 days with a negative ΔGP last summer at those locations.
In addition to showing the number of days at these locations with negative ΔGP during the summer of 2022, I also plotted the points at their average air temperature on those days. A few of these locations are unlikely to have cool-season grass. Or will have some cool-season grass, but only for winter overseeding.
Then there are places like Shanghai, Dallas, Madrid, Fukuoka—you can find a location near you on the chart—where there are plenty of creeping bentgrass greens, and where it is really hot in the summer.