12 June 2013

Why Is Colorado Afflicted With Fire and Smoke?

Yesterday, Denver set a new record with a high of 100 degrees, several degrees higher than the previous June 11 record set in 1956 and the earliest 100 degree summer day in Denver history. 

The heat and dry conditions weren't limited to Denver.   The successive days of record heat created conditions that produced several major wildfires across Colorado yesterday, many of which are still burning. 

At least eighty homes have been destroyed by the Black Forest fire in a subdivision to the North of Colorado Springs that has grown to 48 square miles and forced about 8,000 people in a mandatory evacuation area to flee as well as many more such as 1,000 people at a Boy Scout camp that are nearby but not yet in the evacuation area. 

Near Canon City, Colorado, three buildings of a popular tourist area have been destroyed by the six square mile Royal Gorge fire, although its famous suspension bridge is currently still standing. 

A 400 acre fire has not yet been contained in the Rocky Mountain National Forest near Estes Park, Colorado during the summer tourist season. 

A wildfire near Walsenberg in Southeast Colorado has reached sixty acres. 

A cigarette butt spawned a fire that destroyed an apartment building in Aurora, Colorado.

These fires across Colorado have produced a heavy haze of smoke lingers over the entire Denver metropolitan area (and beyond) today.

Causes and Context

This isn't terribly unusual in Colorado.  Colorado has endured several years with very damaging fire seasons since I moved here in the mid-1990s and they seem to be getting worse.  Episodic periods of smoky haze, multiple wildfires that destroy many structures and scorch thousands of acres, and slight instances of carelessness that produce massive property damage seem to be the new normal in Colorado.

Mostly, the fires produce massive property damages in the hundreds of millions or billions of dollars per severe fire season, but comparatively modest injuries and loss of life to people.  But, every new fire is a potential catastrophe when it comes to loss of human life.  So far, we've just been lucky.

Those inclined to see larger trends in these events can look to several large scale factors driving them.

* Pine beetle infestations over the past decade or two have created unusually large quantities of fuel for wildfires across most of Colorado.  Large areas of Colorado's pine forests have huge swaths of dead trees.  This isn't entirely independent of hot, dry recent conditions.  Trees in marginal climate conditions are more vulnerable to infestation.

* A long period of zero tolerance fire suppression starting around the 1950s prevented less epic wildfires that occur naturally from clearing out dead wood and flammable materials.  So, large swaths of highly flammable forest have reached a tipping point making them highly vulnerable to massive wildfires until a huge wildfire purges this material.

* The vast majority of modern fires, however, have human rather than natural causes, even if the human causes amount to only slight negligence.  But, this was far less of problem when Colorado was sparsely populated and had few people living in its mountain forests and dry wild grass plains, and when most of those people were natives to the region who had been acutely aware of the risks since they were children.

As more people are squeezed into an arid state, there are more potential sources of ignition for fires.  And many of those people are non-natives of the arid west aren't sensitive to the risk of harm associated with slight carelessness with potential fire sources.  In particular, many nature loving people have moved into particularly high fire risk "stupid zones" without uniformly taking maximal precautions.  The fire risk associated with urban-wild interface areas where 100% of residents are careful may be modest, but if just 99% of residents are careful, the measures taken by everyone else scarcely matter at all.  The force of nature that is a many thousands of acre wildfire in extreme heat during drought conditions on a windy day can overcome almost any precautions an individual home owner could take against this risk.

* Most of Colorado has experienced sustained periods of drought and record high (for recorded Colorado history) temperatures.  Some of this is due to multi-year ocean current driven weather cycles like El Nino and La Nina, in the Pacific Ocean.  Some of this weather, either directly via higher temperatures or via unusual extreme exaggerations of these long term weather cycles may be driven by an powerful overall global warming trend that is driven by human caused air pollution's impact on the atmosphere.

Historically, droughts are climate events of very broad geographic extent.  If you cluster historic drought data for the United States, the vast majority of the nation's historic drought experience can be accurately modeled by breaking the continental U.S. into about eight or ten geographic regions (isolated mountain valleys and coastal areas affected by quirky currents require far more regions to get to 100% of the United States), and those regions are not themselves fully independent in a statistical sense - they are just distinct enough to not be perfectly correlated.

Looking back over periods of thousands of years, which tree ring and other similar evidence makes possible, we also know that multiyear droughts are not unprecedented.  Like earthquakes and floods, drought severity (including duration) is roughly proportion to drought frequency.  Longer more severe droughts are rare, but the pattern of less severe droughts over a long time period can be used to make reasonable estimates about the likelihood of very severe droughts that are black swan events beyond the realm of experience of anyone alive today.

We are in a period of sustained aridity in the western United States that has already lasted several years and could conceivably continue or a decade or several decades (the odds of which are biased by human caused global warming even if it is not necessarily a simple cause and effect relationship). 

A prolonged drought destroyed a whole civilization in the American Southwest about a millennium or so ago (give or take a century or two).  Other prehistoric world civilizations have faced similar fates in the face of prolonged droughts over large geographic areas.   We could be entering a similar climatic period, although our greater understanding of the circumstances and improved technology will probably give us a greater ability to maintain our civilization in the face of such challenges that our prehistoric ancestors.

No comments: