All of us have been touched by the stories of the Colorado floods. This particular natural disaster is occurring in an area not known for flooding. We are used to hearing about fires, or mudslides, or avalanches in Colorado. But while floods are apparently not uncommon in Boulder, I think most people assume “high and dry” when they think “Colorado”.

According to NOAA, a cold front stalled over the state, and came into contact with monsoonal air. The clash between the two led to heavy, heavy rain. Colorado’s Front Range was hit, from Colorado Springs north to Fort Collins. Boulder County was hit the hardest. By September 12th, 9.08 inches of rain was recorded there. That number nearly doubled to 17 inches by September 15th. Seventeen inches is about the average annual rainfall for a year. In other words, in a 3 three-day period, this area was inundated with the same amount of rain it would normally have had spread throughout one year.

One of the difficulties when you’re far away from an event and trying to understand is finding sources for information that are informative and accurate. Colorado happens to be home of some of the most interesting environmental studies programs in the country, one of which is at the University of Colorado Boulder. Professor Roger Pielke Jr.’s Blog is a good place to start. Professor Pielke is a professor at the Center for Science and Technology Policy Research at the University of Colorado Boulder. If you click around his blog posts, you’ll quickly find other interesting analyses.

Something Professor Pielke talks about here is the notion of a 100-year flood and the misunderstandings that arise with the use of the N-year flood terminology. The “100-year flood” is something you’ll see a lot of if you search the internet for information about the Colorado floods, along with the “1000-year flood”. It appears that what Colorado has experienced is a 1000-year rainfall, and a 100-year flood. What this means is that such a large rainfall in that area has a 0.1% chance of being exceeded in any given year, and the flood they experienced is one that has only a 1.0% chance of being exceeded in any given year. While we sometimes refer to the N-year event, it’s also frequently critiqued for being confusing because people often think it means that such events will only happen once in a 100 years. In fact, as Professor Pielke explains, this is not the case. There’s no doubt that Colorado has suffered a bad flood, and a bad rainfall, but the terms 100-year and 1000-year have nothing to do with the idea that these weather events will only happen once in a hundred years or once in a thousand years.

First, the use of the N-year to describe the possibility of an event occurring in any given year is pretty deeply embedded in a lot of our flood control and emergency management policies. See for example, the way it is used for determining flood zones by FEMA.

Second, the use of any N-year term in all its ambiguity and confusion is loaded with symbolic meaning, and not just what the mass media and some policymakers propagate. While I can only speak of this anecdotally, my experience with victims of the 2011 Mississippi floods is that immediately after the event and for at least a year later, the terminology was like a life-preserver on an emotional level for some of them. For some, it gave validation that they had experienced something not only horrific and but also highly unusual. At a point when it was very important to believe that normalcy could be restored, it seemed to me that the unusualness of the situation provided them with hope and a will to move forward with rebuilding. Now, two years later, I’ve heard some mull over the term, noting that they had not understood it correctly at the time, and quite consciously concerned about what it will mean for river management in the future. Part of their continuing attention is due to a call for new policymaking along the river, but part of it is because they’ve had time to learn about the various issues that gave rise to the flood and the difficulties of river management. They are continuing to process the experience while still living through its aftermath. The meaning has changed for them, but they needed some distance from the critical event itself in order to begin to think through its many implications for their future.

While I don’t know the degree to which the term is being used in Colorado’s disaster victims (and would invite comments about the meaning of this term to the people who experienced the rainfall), it is certainly being used in the press. And, it will have symbolic power not only for those who use it in the press, but also for all who hear it. Those of us who use the term because of its salience in public policy need to deploy it with caution. At the same time, being too quick to dismiss the emotional importance of the term to those who are dealing with the stress of living through a disaster may also be damaging to the disaster management processes that needs to take place in any setting where a natural disaster has occurred, including Colorado.

I hope everyone becomes skeptical of the term and learns to listen carefully when they hear it, to discern how it is being deployed by the speakers and asking themselves what the speaker’s goal is in using it. It would be nice if we would stop using N-year measures altogether, but since FEMA and other organizations use it for disaster planning and to describe weather events, we’re probably stuck with it for quite some time.

But it can be deeply misleading, and one place it leads people is to the idea that, once they’ve recovered from a disaster, it will not happen again in their lifetime — or their children’s. Or in their children’s children’s future. Unfortunately, it may. Where it has flooded once, it can flood again. Even a small amount of flooding can cause vulnerable populations to lose everything they have built in their lives for some length of time, setting them back several years financially. An extreme flood can wipe out generations of wealth building. In the decisions that will follow concerning rebuilding and recovery, thinking through what the term means for the people living where the event has just occurred who may be facing it for the first time, will be incredibly important to gaining support for rebuilding in a way that will make everyone safer. And, knowing that there will likely be a learning curve in understanding flooding, flood management and flood control, strikes me as an essential element in the task ahead of disaster managers and policymakers.

A great deal of ink has been spilled on all these ideas and from a wide variety of perspectives, but for some further reading complexities of flood management and the symbolic power of terminology in environmental policy, here are some places to look:

T.A. Birkland (2007). Lessons of Disaster: Policy Change After Catastrophic Events. Georgetown University Press.

T.A. Birkland (1997/2007). After Disaster: Agenda Setting, Public Policy and Focusing Events. Georgetown University Press.

S.D. Brody, S. Zahran, P. Maghelal, H. Grover, and W.E. Highfield (2007). The Rising Costs of Floods: Examining the Impact of Planning and Development Decisions on Property Damage in Florida. Journal of the American Planning Association 73(3): 330-345.

B. Merz, J. Hall, M. Disse and A. Schumann (2010). Fluvial Flood Risk Management in a Changing World. Natural Hazards and Earth System Sciences 10: 509-527.

R.A. Pielke (1999). Nine Fallacies of Floods. Climate Change 42: 413-438.

K. Tierney, C. Bevc and E. Kuligowski (2006). Metaphors Matter: Disaster Myths, Media Frames, and Their Consequences in Hurricane Katrina. The Annals of the American Academy of Political and Social Science 604(1): 57-81.