Minutes of the November 23, 2009 Meeting
Smoky Mountain AMS Chapter
Around eight people met for dinner at Calhouns on the River in Knoxville. After dinner, around fifteen people met on the UT Ag campus to hear Dale Kaiser (Oak Ridge National Laboratory) speak about "Reconstruction of False Spring Occurrence over the Southeastern U.S., 1901-2007: Increasing Risk of Spring Freeze Damage?". The following was an abstract of his talk:
"Near-record warmth over much of the United States during March 2007 promoted early growth of crops and vegetation. A widespread arctic air outbreak followed in early April, resulting in extensive agricultural losses over the southeastern U.S. This ‘false spring’ event also resulted in widespread damage to newly grown tissues of native deciduous forest species, shown by previous researchers to have affected the terrestrial carbon cycle. The current study reconstructed the historical occurrence of false springs for the southeastern U.S. (32-39 °N; 75-98 °W) from 1901–2007 using daily maximum and minimum temperature records from 176 stations in the Global Historical Climatology Network database, and Enhanced Vegetation Index (EVI) data derived from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations. A false spring index was introduced that examined the relative timing of the start of the growing season (SGS), or leaf emergence, to the timing of a potentially damaging last hard freeze (? -2.2 °C). SGS was modeled for the domain by combining EVI data with ground-based temperature ‘degree-day’ calculations reflecting the rate of springtime warming. No significant area-wide, long-term SGS trend was found (0.2 days later/decade; p = 0.3). However, the timing of the last hard freeze did occur significantly later (> 1 day/decade; p < 0.05) over a contiguous region stretching from Mississippi eastward to the Carolinas. False spring risk also was found to be increasing over the same area, although a domain-averaged trend showed no change in risk since 1901. These results illustrate the complexity of observed climate change over the last century. In a generally warming world, the character of temperature changes in some regions does not result in decreasing risk of false spring, and may in fact pose increased risk if occurring during vulnerable plant growth stages."
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