For flooding it is a typical estimation from modelling from things like topography maps and known precipitation events. It is all rough estimations without collecting monitoring data, which is what funding for these agencies tend to be used for.
It requires a lot of information to accurately model and predict if any given river valley can handle 1.75 inches in a 3 mile radius in 4 hours, versus 3.25 inches in a 1 mile radius in 2 hours. How much does a 0.2 inch rainfall event in the previous 24 hours impact? What about 1 inch in the same area in 24 hours? (And so on.)
For flooding it is a typical estimation from modelling from things like topography maps and known precipitation events. It is all rough estimations without collecting monitoring data, which is what funding for these agencies tend to be used for.
It requires a lot of information to accurately model and predict if any given river valley can handle 1.75 inches in a 3 mile radius in 4 hours, versus 3.25 inches in a 1 mile radius in 2 hours. How much does a 0.2 inch rainfall event in the previous 24 hours impact? What about 1 inch in the same area in 24 hours? (And so on.)
Ok that makes sense. Thank you. It’s a really fascinating subject to me