Dealing with Storm Damaged Timber in Alabama
Two separate storm events on April 15, and April 27, 2011 impacted 39 Counties in Alabama. The tornadoes of April 15th caused damage in 13 Counties with most of the damage inflicted in rural areas. These tornadoes exhibited typical patterns where damage along the track was intermittent with touchdowns and liftoffs occurring sporadically. The tornadic events of April 27th were spawned from supercell activity and demonstrated behavior typical of storm events occurring in the Great Plains region with extremely powerful tornadoes tracking for long distances after touching down. These outbreaks caused damage in 33 Counties some of which were impacted by the April 15th tornadoes. Typical of tornado damage, the impact to the forests of Alabama was incurred along the tracks of the tornadoes with almost total devastation of the standing timber. Depending upon the strength of the tornado the damage path would span anywhere from ⅛th of a mile to a full mile in width. The Alabama Forestry Commission has created a website specifically devoted to the recent tornados.
Tornado Damage Assessment with Landsat Imagery
A Landsat satellite scene was acquired on May 8, 2010 by NASA that provides a much clearer picture of the damage caused by the EF-4 tornado that struck the state of Mississippi on April 24, 2010. A Normalized Difference Moisture Index (NDMI) differencing procedure with thresholding was used to locate the areas of damage and also to assess the scale of which the damage occurred. Landsat provides a much higher resolution (30m) picture storm damaged areas than that of the MODIS satellite (250m) previously used. The Landsat imagery can provide a stand-by-stand assessment of damage caused by the storm that can be utilized by both public and private forest landowners to allocate resources for assessment and recovery of timber damaged by the storm.
Rapid Assessment of Forest Damage from the April 24, 2010 Tornado Event in Central Mississippi
A tornado went through central Mississippi on April 24, causing massive damage and loss of life. The tornado developed over northeast Louisiana and proceeded in a northeasterly direction for about 150 miles. At its largest point, the twister was recorded at 1.75 miles across with winds reaching 170 miles per hour. The Mississippi Forestry Commission reported the value of timber damaged at over $19 million, with some 62,000 acres impacted by the storm.
College of Forest Resources' doctoral candidates David Wilkinson and Michael Crosby have analyzed satellite imagery to determine the scale of devastation. The assessment can be a vital tool for large-scale land managers that need to determine where they should allocate their assets for post-storm salvage harvesting.
Moderate Resolution Imaging Spectroradiometer (MODIS) imagery provided by NASA was used to develop the assessment. The imagery is produced from two satellites that provide daily imagery of the continental USA at a 250 meter resolution in a number of visible and infrared banks. The Mississippi State students acquired imagery on April 20 (pre-storm) and on April 29 (post-storm). The students developed a Normalized Difference Vegetation Index—a simple numerical indicator that can be used to analyze remote sensing measurements—to assess the vegetation damage (primarily forested areas) along the track of the tornado.
Damage from the storm can be seen in the true color MODIS image taken five days after the storm. The area of change and scale of the damage that occurred along the tornado track in seven counties in central Mississippi is also visible. While the tornado was on the ground further to the west of the study area, clouds and a lack of pre-storm vegetative cover in the delta counties of Mississippi and Louisiana prevented damage from clearly being seen.
NDVI differencing threshold image showing damaged areas through seven counties in central Mississippi. Colors indicate: Green-Light Damage, Yellow-Moderate Damage, and Red-Heavy Damage.
April 29th true color (bands 1,4, and 3) MODIS-Terra imagery of tornado track through Yazoo and Holmes counties in Mississippi. Red arrows show tornado path.