El Niño and La Niña years and annual area burned in Arizona and New Mexico. Note that a greater area burns during La Niña years (dry winters) than during El Niño years (wet winters). The pattern is one of wet El Niño years creating a build-up of fine fuels (grasses and shrubs), which then dry out and ignite more effectively during the dry, warm La Niña years. This pattern is confirmed by individual fire history analyses at many sites throughout the Southwest (see Climate Fire Analysis for more information).

Credit: Tom Swetnam and Julio Betancourt. Updated from Swetnam, T.W., and J.L. Betancourt, 1990: Fire-Southern Oscillation relations in the southwestern United States. Science 249:1017-1020.