Water

We had the discussion of the “1,000 year flood” on this blog earlier here so I thought I would post this followup information from a seminar at CU this week…from Roger Pielke, Jrs.’blog here.

His post seems to address the point we stumbled upon in our discussion here.

In an article titled “The Science Behind Colorado’ Thousand-Year Flood” Time magazine explains:

Parts of Boulder are experiencing a 1-in-1,000 year flood. That doesn’t literally mean that the kind of rainfall seen over the past week only occurs once in a millennium. Rather, it means that a flood of this magnitude only has a 0.1% chance of happening in a given year.
Time is a fixture of the mainstream media and what is written there is widely read and repeated.

A big problem with Time’s article is that Boulder did not actually experience a “1,000-year flood.” In fact, according to an analysis presented by fellow CU faculty member John Pitlick yesterday, using standard hydrological methods, Boulder experienced between a 25- and 50-year flood. (I am focusing here on Boulder, I have not seen similar analyses for other Colorado streamflows, though they are sure to come.) Pitlick further noted that the flood waters did not reach the 50-year flood marker on the Gilbert White memorial (seen at the top of this post.)

Pitlick walks us through maps of estimated inundation for 25-yr, 50 & 100 flood. Observations over recent days look more like 25-yr maps.

How is it that the “1000-year flood” has come to characterize the flood in Boulder? Let’s take a quick look.

The Time article points us to an article on the floods at Climate Central, a non-profit group focused on reporting all things climate change. That article made the following claim:

The Boulder, Colo., area is reeling after being inundated by record rainfall, with more than half a year’s worth of rain falling over the past three days. During those three days, 24-hour rainfall totals of between 8 and 10 inches across much of the Boulder area were enough to qualify this storm as a 1 in 1,000 year event, meaning that it has a 0.1 percent chance of occurring in a given year.

So right away we see an error. Climate Central was discussing rainfall which Time mistakenly converted into floods. They are not the same thing. As John Pitlick explained yesterday, return periods for rainfall and flooding for the same event can vary by several orders of magnitude.

Having heard much of the Santa Fe and the Denver Water partnerships, it was interesting to get Char’s historical and southern California take in his piece here. I have to note that the former R-2 Regional Forester, Rick Cables, and Harris Sherman were known for speaking about water pretty much incessantly. To the extent that Dave Steinke made a series of clips of just Rick saying the word “water”, that was a hoot. Anyway, it’s good to see the Chief talking about it.

My only comment is that I don’t think the idea of “tight ecological relationship” was maybe what they were thinking back in the 19th century. I don’t think the term was used that way back in the day.

Here’s an excerpt:

No one better understood the power of water to define life in the American west than the 19th-century activists and scientists who articulated the need for the creation of the national forests. They predicated their arguments on a close reading of the land and the tight ecological relationship they believed existed between upstream watersheds and downstream economies.

To sustain healthy forests and clean water was what led George Perkins Marsh, John Wesley Powell, George Bird Grinnell, and Bernhard Fernow — directly and indirectly — to champion a more robust federal regulatory presence on the public domain. Without some form of control exerted over these landscapes and the common (and wet) resource they provided the opportunity to establish communities in this oft-arid terrain would dry up.

This conception was woven into what would become the Forest Service’s organic act, legislation enacted in 1897 that defined how the “forest reserves” were to be organized and administered, and on what basis: “to improve and protect the forest within the reservation…securing favorable conditions of water flows, and to furnish a continuous supply of timber for the use and necessities of citizens of the United States.”

Note that water took sequential priority to timber, an ordering that leads to a reconceptualization of the significance of the Forest Service’s name: its managerial actions are in support of the ecosystem services its high country woodlands provide, whether in the Rockies, Wasatch, or Cascades, the Appalachian or Alleghenies, the Sierra, Santa Anas, or San Gabriels.

Note, too, that each of these ranges, and the others over which national forests are draped, bear a direct connection to lowland communities dependent on the rivers, streams, and creeks whose sources lie in the mountains above. This is not by happenstance. Residents of those valley cities and basin towns were among the most powerful proponents of the national forests in the late 19th and early 20th centuries. Worried about the deleterious impact that rapid timber harvests, wildland fires, and grassland overgrazing were having on local potable water supplies, they pushed hard for federal oversight.

This was as true of San Diego’s advocates of the San Jacinto Forest Reserve (now part of the Cleveland National Forest) as for those in San Bernardino and Riverside who promoted what would become the San Bernardino National Forest. They, like their peers in Ashland, Oregon who championed the Rogue River National Forest, and in New England who fought to secure the White Mountain National Forest, appreciated how integral these natural systems were to their daily lives; healthy forests meant healthy humans.

We were discussing something earlier on this blog, and it seemed that this information might be relevant.
It is now out of date, as it was based on 2000 Census Data, but you can get the general perspective.

Here is a pdf, in case you want to see more clearly.