Implications of the Spring Freeze of 2007

摘要

Spring 2007 in Tennessee was drier than normal, but otherwise plants in nurseries and landscapes were in very good shape. According to the Normalized Difference Vegetation Index (NDVI), a measure of the greening of the canopy of the forest collected by the National Oceanic and Atmospheric Administration (NOAA) at the Walker Branch Watershed in Oak Ridge, Tennessee — green-up of vegetation was 3 weeks earlier than in 2006. This was due to higher than normal temperatures. In most regions of the state,temperatures had reached temperatures of 21 to 27 deg C (70 to 80 deg F) by late March. During the first week of April, flowering dogwood (Cor-nus florida) was in full bloom. Weather conditions were about to change drastically. In Murfreesboro, Tenn,the geographic center of Tennessee, the daily high on April 4 was 27 deg C (80 deg F) with a low of 10 deg C (50 deg F). By April 6, the daily high was 10 deg C (50 deg F) with a low of -1 deg C (30 deg F). On Easter morning, 8 April 2007, the temperature dropped to -7 deg C (19 deg F), this was repeated on 9 April when the low was again -7 deg C (19 deg F). Record low temperatures were reported at nearly all reporting stations in Tennessee. In Crossville, Tennessee on the Cumberland Plateauat nearly 610 m (2,000 ft) elevation, the record low was -11 deg C (13 deg F). In many of the areas where nursery stock is grown, lows ranged from the high teens to low twenties. In addition to record lows, other factors played a role in plant damage.Firstly, the mid-South region was already in a moderate to severe drought. Secondly, the duration of the cold temperatures undoubtedly added to the intensity of the damage. At Crossville, Tennessee, from April 4 to 10, temperatures below 0 deg C (32 deg F) were recorded for 70 h.