Climate Impacts on the 1999 U.S. Wildfire Season

Though fuels were readily available to burn across virtually all of the primary wildfire locations in the U.S. this past year, only Nevada and California had extreme seasons. In Nevada, it was the largest number of acres burned in recorded history, and California ranked number three in acres burned on state managed land. In other parts of the country, the potential for fire seemed high, yet the seasons were not extreme. These included the northeast in conjunction with the summer drought, and the southwest in conjunction with La Nina and dry winter and spring conditions. Climate factors impacting the 1999 U.S. wildfire year will be discussed in this presentation. Station data and NCEP/NCAR reanalysis surface and upper-air variables are examined in relation to the season’s fire activity. For example, the strength of this summer’s southwest monsoon kept the fire potential at a minimum in that region. Low surface relative humidity and dry thunderstorms were largely responsible for Nevada’s record season. In California, above normal surface wind speeds greatly affected the strength of their season. These various factors imply that a number of climate variables must be considered as potential impacts on wildfire, versus single variables often attributed to many other climate regional impacts (e.g., precipitation – drought or flood; temperature – heat wave or record cold). Using this variety of climate information for fire management planning will also be discussed.