The University of Arizona

What’s New in SW Climate Research?

December 26, 2011
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Two weeks ago in San Francisco, 30,000 scientists from all over the world gathered to present their research at the American Geophysical Union (AGU) Fall Meeting. Topics ranged widely from imaging of the Moon’s core using seismology to carbon sequestration in soybean crop soils to methods of communicating science. Out of all of these presentations, hundreds were about ongoing research in the Southwest. I’ll highlight a few here, but if you’d like to read more, the abstracts can be found online at the fall meeting website. Simply go to the Scientific Program drop-down menu on the left and select the Itinerary Planner. Then select the “Continue as Guest” button and you can search for any abstract. Most of these studies and results are preliminary, but will hopefully be published soon.

Gerald Meehl from the National Center for Atmospheric Research (NCAR) presented observations of temperature in the U.S. that show an east-west gradient in temperature extremes (Abstract ID: GC13C-03). As the climate warms due to increasing greenhouse-gas concentrations, record highs are expected to occur more often than record lows. In fact, in 2011 in the U.S. this was just the case, with record highs outnumbering record lows by 3 to 1. What’s more interesting, however, is that for the western U.S. this ratio was 3.4 to 1, but for the eastern U.S. it was 1.8 to 1. Meehl showed that the majority of models aren’t able to reproduce this east-west gradient, and thus the relative ratios of record highs to record lows. One model simulation that does capture this gradient, however, shows that tropical Pacific sea surface temperatures (El Niño) can alter this gradient, and thus the ratio of record highs to record lows in each region.

Another study presented by scientists in New Mexico, Arizona, Tennessee, and New York uses tree-rings from throughout the Southwest to reconstruct a record of regional drought stress from 1000-2005 AD in order to determine how normal the early 2000s drought was in comparison to the last 1100 years (Abstract ID: GC31A-1011). They found a 20-year megadrought throughout the Southwest from 1575-1595 which was much worse than the early 2000s drought. Thus, more severe droughts than those we have seen in the instrumental period have occurred naturally in the past and therefore are likely to occur again in the future. What’s more, with increasing temperatures and changing precipitation rates due to climate change, the scientists suggest that we may migrate out of the realm of “normal” drought variability in the next few decades as temperatures continue to rise higher than they have in the past.

Another drought study, this time combining a regional model with water isotopic analysis of aspen trees, seeks to determine the elements of drought that are most associated with recent widespread aspen forest die-off across much of the western U.S (Abstract ID: GC31A-1010). The scientists, from California and Idaho, analyze the roles of drought seasonality, severity, and duration on this die-off event by using a watershed-level model and isotopic analysis of the water within the aspen tissue. These isotopes suggest that aspens have a limited ability to draw on deep water when under seasonal water stress. In addition, the regional model found that spring temperatures and water deficits during spring and summer were the two variables that best explained aspen mortality. Thus, with high spring temperatures and water stress during spring and summer, aspens have difficulty drawing on deep water reservoirs, resulting in widespread mortality.

Changing gears a bit, John Sabo from Arizona State University discussed water policy in the Colorado River Basin and provided a framework for improving streamflow levels by 21% current levels (Abstract ID: H42D-05). John and his colleague—Robert Glennon from the University of Arizona and author of the book Unquenchable—first specify this restoration target of 21% streamflow improvement, then determine how much water cities and farms can withdraw to achieve this target. Finally, they propose implementing a region-wide water pricing system in order to collect money and provide cities and farms with the means to achieve these withdrawal goals. For example, the money can be used to improve irrigation efficiency on farms, provide reclaimed water systems to major urban centers, and stimulate non-governmental organizations to buy back water from the agricultural sector.

Other climate-related studies relevant to the Southwest that were presented at the conference include using a hydrologic model to find the impact of climate change on the Salt and Verde Watersheds in Arizona, using satellites to measure groundwater, and using regional climate models to assess climate change impacts on ecosystems and agriculture. These studies are only a handful of the hundreds presented on the Southwest at the conference. Scientists from around the world are continuously producing new and exciting research, and conferences like the AGU Fall Meeting provide a stimulating medium for discussion and potential collaborations. If these presentations are any indication of the breadth of southwest research that will be published next year, it should prove to be a very exciting year!

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