February 5, 2008

I guess it’s no surprise that climate change is also affecting the natural cycles of the American Southwest, and the threat on our already tenuous and over-apportioned water supply will continue to increase as human-induced global warming wreaks its havoc on our ecosystems.

From the newsletter of the Rocky Mountain Climate Organization (italics mine):

Study Finds Human-caused Climate Change Disrupts the West’s Hydrologic Cycle

The first study to definitively show that observed changes in the hydrology of the West’s major river basins are likely caused by human-induced climate change was published in Science Express on January 31 (in abstract form only for free; readers can elect to purchase the full article online). The authors of the study include well known climate researchers from around the West. Based on observations of nine mountainous regions of the West for the period 1950-2000, the researchers found that up to 60% of the trends of warmer winter air temperatures, declining snowpacks, and earlier run-off can be attributed to human-caused climate change, rather than natural variability. In all but one range (the Sierra Nevada), water content of the snowpacks decreased, and in all ranges the January through March average minimum temperature increased, and peak river flows occurred earlier in the year. The results were compared with a regional hydrologic model downscaled from two global climate models. The anthropogenically forced versions of the models led the researchers to verify the correlation between the model predictions and the observed hydrologic changes.

Climate-change realities could ruin water planning, Phoenix Arizona Republic, February 1, 2008. In Arizona, an unusual warm winter rain in the mountains of the Verde River watershed seemed to bear out the implications of the study. The basin’s reservoir managers were not prepared for the unexpected volume of early season run-off and were forced to let much of the water flow through the reservoirs unstored. “That’s a harbinger of the future right there,” said Brad Udall, director of the Western Water Assessment. “Reservoirs actually need to get drawn down to get ready for spring runoff and for any additional rain. Because rain intensity is expected to increase with warmer temperatures, we’re probably going to have to draw reservoirs down lower in the spring. In some years, we could wind up with less water stored. The old rules don’t apply anymore. The real problem is we don’t know what we’re going to replace them with.”

Posted by Emily Long

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