Dry Times for Western North America, Climate Trends Forecast

Get ready Western North America, climate change is well upon us and the trends so far spell D-R-Y, as in very dry.

Researchers Overpeck and Udall*, writing in a recent ‘perspectives’ report in Science Magazine (Climate Change: Dry Times Ahead, 25 June, 2010), cite a litany of  troubling trends to support their prediction:  “soaring temperatures, declining late-season snow pack, northward-shifted winter storm tracks, increasing precipitation intensity (note: not total rainfall), the worst drought since measurements began, steep declines in Colorado River reservoir storage, widespread vegetation mortality, and sharp increases in the frequency of large wildfires.”

The effects of global warming and climate change on Western North America are mounting and bode for a much dryer climate in the coming decades.

Wildfires are distinguished from other types of fires (such as brush, peat, and veld fires) by their cause, size, rate of propagation, ability to shift direction rapidly and jump barriers like roads and rivers. Although wild fires create soil conditions that are vital to the growth of some forms of vegetation (through what’s known as ecological succession) , they can also cause extensive ecological damage, in addition to being destructive to human life and property.

The mountain pine (bark) beetle, Dendroctonus ponderosae

Another common by-product of warming/drying trends is an increase in certain pests and tree/plant pathogens (such as fungi and viruses). Indeed, the ‘mountain pine’ beetle (a member of the Dendroctonus–“tree killer”– genus) has been rapidly spreading through, and decimating, western pine forests–from New Mexico to British Columbia–since 2006. Millions of acres in Montana and Wyoming have already fallen prey and turned rust red (due to a complete loss of chlorophyll).
Pine trees can defend themselves from an infestations by secreting more white resin to seal off the beetles’ egg burrows. But the beetles also carry a blue-stain fungus that secrets a protein able to block the resin flow–as well as the food flow to the tree. Trees that succumb to this attack die from starvation. Though population blooms of the insect are normal following hot summers, it is believed that climate change trends, in the form of hotter temperatures and less rain help provide the ideal conditions for these and other parasitic insects to expand their populations and ranges

The researchers,  Overpeck/Udall, also note that these climate change-related developments are occurring over a region that also saw the greatest population growth.

Such population growth is already putting water usage pressure on the Colorado River, with water “deliveries” (to various regions and cities) increasing annually. The Colorado River (and reservoir) currently supplies 27 million users in 7 states and 2 countries and irrigates over 3 million acres of farmland. And, according to a 2008/9 assessment paper (Barnett and Pierce, PNAS, March 2009), “Global climate models almost unanimously project that human-induced climate change will reduce runoff in this region by 10–30%.”

These latter  researchers also conclude that “With either climate-change or long-term mean flows, currently scheduled future water deliveries from the Colorado River are not sustainable.” However, they also assert that the ability of the river system to mitigate  the effects from drought  “can be maintained if the various users of the river find a way to reduce average deliveries.”

Clearly, with increasing population growth in this region, and the fact that such water delivery orders (measured in billions of cubic meters per year) are based upon annual population usage multiplied by expected growth, managing and achieving a sustainable level of water usage (of the Colorado River system) in this region will be a considerable challenge. Forecast

*Main Cited Researcher affiliations:  Jonathan Overpeck – Climate Assessment of the Southwest, Univ. of Arizona;  Bradley Udall – Western Water Assessment, Univ. of Colorado

top photo:  Wildfire in California, Sept. 5, 2008.  BLM

Beetle image: USDA

The effects of global warming and climate change on Western North America are mounting, and bode for a much dryer climate in the coming decades.

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