We can look at temperature data for Seoul and Philadelphia and we find that the average temperatures throughout the year have almost complete overlap. So we might expect that with such similar temperatures on a month by month basis, the grasses used in those cities would be similar. But while the courses at Philadelphia are mostly cool-season grasses, what we find at Seoul are primarily courses planted to Zoysia japonica. Here is a dormant zoysia fairway near Seoul in early spring.
Why such a different choice of grass when the temperatures are the same? I suggest that it has to do with summer precipitation.
From June through September, Seoul has a higher monthly average rainfall than does Philadelphia, and during the two hottest months of the year, July and August, Seoul has more than three times the rainfall, on average, than does Philadelphia. This combination of high temperature with high precipitation can be deadly for cool season grasses.
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