My column in the November/December 2015 issue of GCM China shows normal temperature and sunshine data from three pairs of cities. I chose Beijing and Philadelphia to represent the cool-season zone, Shanghai and Atlanta to represent the transition zone, and Guangzhou and Tampa to represent the warm-season zone.
In each of these pairs, the temperatures are similar. In the transition zone and warm-season zone pairs, the sunshine hours are quite different, and it is the locations in the USA with higher sunshine. From the sunshine hours, one can estimate the daily light integral (DLI). As I wrote in the article:
Each sunshine hour is equivalent to about 5 moles of photons per square meter. Taking the month of May as an example, on a normal day in Guangzhou, there would be 4 hours of sunshine, in Tampa 10, in Shanghai 5.5, and in Atlanta 9. This gives an approximate DLI of 20 in Guangzhou, 50 in Tampa, 27.5 in Shanghai, and 45 in Atlanta. Bermudagrass grows best when the DLI is above 40.