Climate Change: Predicting Colorado's Future

Citizens of Colorado seem to enjoy pointing out the fortuitous nature of the state’s climate. "Don’t like the weather?" they say, "don’t worry, it’ll soon change." If it is difficult to predict the weather on a day-to-day basis, how could anyone hope to predict the effects of climate change in the future? Even the most generalized predictions are helpful, as the same attractions that bring people to live in Colorado--skiing on snowy mountains or hiking in lush evergreen forests--are dependant on the climate. The same folks who comment on the climate depend on it as much as natural ecosystems-urban areas and agriculture rely on spring snowmelt to provide water. So, small changes in temperature and precipitation may affect the state in drastic ways. Accurate predictions are more than useful--they are necessary if Colorado wishes to be adaptable.

How can accurate predictions be made? If we study Colorado’s past, distant and near, we can get an understanding of what might happen to the state if temperatures rise. The near past gives us temperature records and historical data, while historical data from the distant past (or even a recent, yet ignored past) must be gleaned from naturals clues. In the past, and likely the future, a rise in temperature has brought about two major potential types of damage to Colorado: drought and insect infestation. Drought conditions in Colorado rely heavily on the amount of snow pack. Destructive insects like the mountain pine beetle, on the other hand, react to small changes in seasonal variations. By studying historical records, scientists have found that both the amount of snow and the destructiveness of the pine beetles are closely linked to small variations in temperature.

Since thermometers and rulers didn’t arrive in Colorado until the mid-1800s, scientists have to look at clues other than the instrumental records, in order to understand the broad variations in climactic conditions. To reconstruct a long-term record of snowpack, Dr. Connie Woodhouse of the NOAA Paleoclimatology Program turned to tree rings. Previously, the tree ring record had been too spotty for such reconstructions, as collection ended in the 1960s. A new set of tree rings were collected from Colorado’s western slope in 2000 and 2001, allowing Dr. Woodhouse to create a fairly accurate model. When she compared instrumental records with the data she gained from tree rings, she found the levels of snowpack estimated by the model closely matched observed records from the 20th century.

To Woodhouse, this comparison was essential for predicting future conditions. She wrote, "This is useful in determining whether planning based on the instrumental record incorporates the range of variability and extremes that is representative of long-term natural variability, and the range of natural variability that is likely to occur in the future." In fact, Woodhouse’s reconstruction showed there was greater variability in the amount of snowpack in centuries other than the twentieth-the last 100 years haven’t been that extreme. She also found that the amount of snowpack in Colorado is closely linked to the El Nino/La Nina cycle of moisture in the Pacific. (Colorado gets more snow in El Nino years and less during a La Nina event.)

A study on the water resources of the Colorado River Basin by a group of scientists at the University of Washington, Niklas S. Christensen et al., suggests that even a small reduction in the amount of streamflow in Colorado would have drastic impacts on the western water supply. Since the Front Range is naturally arid, water has been piped across the continental divide through aqueducts and canals to supply homes, ranches, and farms. But Coloradans don’t have the only claim on the water from the western slope. Seven other states and Mexico also depend on water from the Colorado River. After a close examination of historical records, Christensen and his colleagues found that while the Colorado River is mostly unaffected by seasonal changes, it is highly dependant on the amount of annual precipitation. With a small rise in temperature, no matter which way it is divided, there will not be enough water to go around. The authors of the study wrote, "In general, because of the (relative) size of the reservoir system, it is unlikely that changes in reservoir operating policies can adequately mitigate the effects of climate change and associated hydrologic changes in the basin."

Not all of Colorado’s future may depend on snowpack, however. A small change in seasonal temperatures can potentially wreck havoc on Colorado’s forests, through the work of one insect species: the mountain pine beetle, or Dendroctonus ponderosae. When entomologist Jesse A. Logan and mathematician James A. Powell teamed up to study the effects of temperature on the developmental cycle of the pine beetle, they found a curious and disturbing pattern. Since pine beetles depend on large populations to sustain attacks on pine trees, the timing and synchrony of reproduction is critical. Pine beetle populations normally develop in erratic patterns, based on warming spring temperatures. In order to understand the effects of seasonal changes, Logan and Powell examined a group of lodgepole pines, once growing on Railroad Ridge in the White Cloud Mountains of central Idaho. This particular grove suffered a severe pine beetle attack during a warm spell in the 1930s, and is now referred to as a "ghost forest". When the temperatures raised by only a few degrees, the developmental patterns of the pine beetles fell into sync, allowing the pine beetles to attack with vigor. For the lodgepole pines, this meant certain death.

The 2005 Report on the Health of Colorado Forests reported that after an unusually dry year, pine beetle attacks rose dramatically. Once mostly confined to the western slope, pine beetle devastation has been cropping up in counties along the Front Range. The dead stands of trees left in the wake of pine beetles provide fuel for forest fires. Added to increasingly dry conditions, thick stands that have avoided fire for decades may be poised to ignite.

Reductions in snowpack, drought, dying forests, and fire hazards: what impact will these have on Colorado’s economy, based largely on tourism and agriculture? Governor Bill Ritter addressed these issues and more in the recently released Colorado Climate Action Plan. This plan suggested water users should work together with government agencies, such as the Department of Natural Resources and Public Health and Environment, for comprehensive drought planning. Likewise, it suggests the US Forest Service work together with other stakeholders in Colorado’s forests to reduce the risks posed by pine beetle attacks. While Colorado’s future may seem bleak, at least the state will be facing it prepared.

All images from relevant papers except "Oblique aerial photo of upper Niwot Ridge and Green Lakes Valley" by Nel Caine, via TundraCam, INSTARR, University of Colorado at Boulder. If this post seems rather limited, that’s because it was a short paper I wrote last semester in an environmental studies class. Given more space and time, I would have gone into more detail concerning the synchronicity of pine beetle breeding as it relates to temperature. That’s a bifurcation (fractal) diagram if I’ve ever seen one.