Search this site:

Climate Change and Extreme Weather-Related Event Data Sources

To date, it is generally believed that hotter and more variable air temperatures will occur across the United States in the future (National Assessment Synthesis Team 2001). However, the timing and distribution of precipitation or other weather phenomena are much less certain (Dale and others 2000). The transient climate change scenarios used for this Assessment do not adequately represent extreme events because of their coarse spatial and temporal resolution (monthly time step, approximately 1,000 square miles) (National Assessment Synthesis Team 2001). Extreme events may last only minutes or days, and their extents may range from local to small regional scales. When the 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, we will discuss the potential impact of projected general trends in extreme weather events on forest structure and function.

Two climate datasets developed by the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP) were used with the PnET-II model to assess future climate impacts on southern forest growth. The Historical Climate Series includes monthly and daily climate data with interannual variability for the conterminous United States from 1895 to 1993 (National Assessment Synthesis Team 2001). The Hadley Centre HadCM2Sul transient climate change scenario was used to represent climate variables from 1994 to 2100; other climate scenarios exist but were not available at the time of this analysis. For the continental United States, the HadCM2Sul 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 (based on IPCC projections of future greenhouse gases) 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 (National Assessment Synthesis Team 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 (National Assessment Synthesis Team 2001).

Predictions of forest area, distribution, and biodiversity used four equilibrium (UKMO, GISS, GFDL-R30, OSU) and three transient (HadCM2Sul, HadCM2GHG, CGCM1) climate scenarios as input for the MAPSS biogeography and MC1 dynamic global vegetation models. The range in temperature increase is 2.8 to 6.6° for all scenarios, with changes in precipitation varying greatly between the scenarios, and changes in CO₂ transient (as with HadCM2Sul) or instantaneously doubling in the case of the equilibrium scenarios. MC1 used only HadCM2Sul and CGCM1, whereas MAPSS used all equilibrium scenarios and averaged the last 30 years of the transient scenarios so they could be treated as equilibria. The BIOME3 model used only the transient climate scenarios (Bachelet and Neilson 2000).