With that relationship known, climate models capable of simulating large-scale circulation and changes in circulation related to climate change could be used to estimate precipitation changes. Previous work along similar lines has relied on observations of monthly total precipitation. The investigators on this project had evidence to suggest that relationships between circulation and precipitation event characteristics, rather than precipitation totals, would be better founded. Their first step was the development of a precipitation event climatology irrespective of the circulation pattern. The climatology shows that in the Southeast there are about 130 precipitation events annually, evenly divided by season.
Most events are less than one hour long and give less than one-tenth inch of rain.
The Appalachian Mountains have longer storms, and south Florida has shorter, sharper ones, than the regional average. In many cases, large parts of the Southeast had correlations significant at the 95 percent confidence level, and occasionally at the 99 percent level. This examination revealed that when atmospheric circulation patterns create airflows coming predominantly from the southwest, areas east of the mountains have long, heavy, and variable events, while western events have the opposite character. Predominantly westerly flow gives a reverse trend. These findings strongly suggest the existence of a connection between continental scale circulation measures and precipitation from individual events, a connection which can be exploited for climate change analysis purposes.