Yesterday (July 18, 2017) we had one of those intense rain events we're seeing with increased frequency. My rooftop rain gauge measured 1.8" of rain in two hours. I was out picking up my daughter at track practice when it hit and got stranded - see windshield shot as I was stopped in a flooded intersection. Last week we had another ~2" rain event.
This morning walking my dog, there was sediment in the streets everywhere. It washed into the Elizabeth and Lafayette Rivers here in Norfolk and was like dumping bags of fertilizer into the rivers. My wife, Dr. Margaret Mulholland, is a biological oceanographer studying algal blooms and she said they are already seeing harmful algal blooms due to last week's deluge...yesterday's "rain bomb" will only add to it.
So going forward we need to add climate change/rain intensity to our stormwater management plans. We get ~60" of rain a year here in Norfolk. If we get 120, 1/2" rain events, no problem, the existing stormwater management systems can handle it. We get 30, 2" rain events, the pollution wins.
This increasing intensity was studied by Peter Popmmerenk who is a planner with the City of Virginia Beach's Stormwater Department. He went to the weather record at Norfolk International Airport and...sure enough, he found an increase in 2" rain events since 1950....measured, not projected from someone's model. The relevant diagram is below - click on the image for his full paper.
Just another part of the challenge with flooding/stormwater.