Extreme Weather

Climate effects on forest conditions are most strongly expressed by extreme events such as hurricanes, tornadoes, floods, drought, and ice storms (Dale and others 2000). Each type of event affects forests differently; some cause large-scale tree mortality, whereas others, such as ice storms, impact community structure and organization without causing massive mortality. (SOFRA-Moore Ch. 18, p. 437-442)

To date, it is generally believed that hotter and more variable air temperatures will occur across the United States in the future (NAST 2001). However, the timing and distribution of precipitation or other weather phenomena are much less certain (Dale and others 2000). The transient climate change do not adequately represent extreme events because of their coarse spatial and temporal resolution (monthly time step, approximately 1,000 square miles) (NAST 2001). Extreme events may last only minutes or days, and their extents may range from local to small regional scales. When effects of extreme events are averaged over large periods of time and space, much information is lost. Therefore, very little quantitative data on extreme weather events are available to predict future forest impacts. Instead, discussed is the potential impact of projected general trends in extreme weather events on forest structure and function. (SOFRA-Moore)

For the Continental United States, the scenario includes a relatively modest 2.8° average increase in air temperature, a 20 percent average increase in precipitation, and effects of doubled CO₂ and altered sulfate aerosol concentrations by 2100 (Bachelet and others 2001). The mean temperature increase for the South is about 1.0° by 2030 and 2.3° by 2100; this degree of warming is smaller than that of any other region (NAST 2001). This scenario predicts that the South will remain the wettest region for the next century; mean annual precipitation increase will be about 3 percent by 2030 and 20 percent by 2100. Other regions in the Eastern United States are predicted to experience similar increases in precipitation (NAST 2001). (SOFRA-Moore)

Each extreme weather conditions, including hurricanes, tornadoes, floods, droughts, and ice storms are discussed in the pages that follow.