The Oklahoma Department of Wildlife publishes a fairly decent pamphlet on fishing subjects. I checked what they had to say about the catfish spawn. Oklahoma has the three main type of catfist - Blue, Channel and Flathead. The information on spawning was identical for all three. Here it is...
Spawning – Spawning usually takes place in late May or early June when the water temperature reaches 75 degrees F. Hollow logs, overhanging underwater ledges or holes under mud banks are typical nesting places. Females lay about 10,000 eggs each. Males guard the eggs against intruders, including the female. The eggs hatch in six to 10 days as determined by temperature. After hatching, fry are attended for a short time by the male as they feed in a dense school.
So, I think the thing which triggers the spawn is water temperature, no matter which geographical region you may be located.