False spring occurrence over the southeastern United States, 1901 – 2007
Garrett P. Marino, Massachusetts Institute of Technology, Cambridge, MA; and D. Kaiser
Near-record warmth over much of the United States during March 2007 promoted early growth of vegetation and many agricultural and horticultural crops. A widespread arctic outbreak followed in early April, resulting in agricultural losses exceeding two billion dollars over the central and 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 models the historical occurrence of false springs for the southeastern United States (32-39N; 75-98W) from 1901-2007 using daily maximum and minimum temperature records from 176 stations in the Global Historical Climatology Network (GHCN) database, and Enhanced Vegetation Index (EVI) data derived from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations. A false spring index was introduced that considers the relative timing of the start of the growing season (SGS), or leaf emergence, to the timing of a potentially-damaging last freeze (≤ 28F). SGS was modeled for the domain by combining EVI data with ground-based temperature 'degree-day' calculations reflecting the rate of springtime warming. While interannual variability of the modeled SGS was large, no significant (α = .05) area-wide, long-term trend was found. However, the timing of the last freeze did occur significantly later over a contiguous region stretching from Mississippi eastward to the Carolinas. False spring risk was also 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 false spring risk, and may in fact pose increased risk if occurring during vulnerable plant growth stages.
Session 9B, Observed changes in climate - II
Wednesday, 14 January 2009, 10:30 AM-12:00 PM, Room 129B
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