I was just contacted by a reporter who is doing a story based on a news release put out by a group called Environment Colorado. The news release says that Colorado has seen a 30% increase in extreme precipitation over the past 60 years, based on a new study called “When it Rains, It Pours” (PDF).

The thing is, there has been no increase in flood damage in Colorado (from 1955-2003 in our dataset), as can be seen in the following graph.

CO Flood.png

This data has only been adjusted for inflation. Given the pace of growth and development in Colorado, one could make a strong case that flood impacts have gone down pretty sharply in per capita or per unit wealth terms. So it may very well be the case that extreme precipitation has increased, but these measures of precipitation are not well correlated with flood damage, which is what Mary Downton and I found in a 2000 study.

Just for fun I also looked at California, which was the subject of a different press release put out by Environment California, and guess what? Extreme precipitation is up 26% in California, and there is no statistically significant trend in damage, even without considering population growth and development.

CA Flood.png

So while human caused climate change may be responsible for changes in “extreme” precipitation, these measures are not well correlated with damaging floods.