Learning About SW Climate > Overview of Fire Research
Recent History

Long-term changes in Southwest tree growth. (View larger image) Credit: Tom Swetnam and Julio Betancourt 1950s pinyon pine dieoff in New Mexico. (View larger image) Credit: Tom Swetnam and Julio Betancourt

Since the 1950s—particularly over the last 20 years—precipitation totals across most of the Southwest have been abnormally high (see section on PDO). Climatologists have noted that since 1976, there have been changes in ocean-atmosphere dynamics that have resulted in more frequent El Niño events, which bring enhanced winter precipitation to the Southwest. As a result of these changes, recruitment of seedlings in Southwestern forests has increased, as has stem growth.

Even with changing vegetation dynamics due to human land use and management, fire-climate linkages through ENSO and the PDO has forecasting value and thus important implications for fire management. Statistical and dynamical models have been developed to predict the behavior of ENSO, which leads Arizona and New Mexico weather by one or more seasons. Extensive fires during the summer of 2000, were preceded by two dry La Niña winters in 1999 and 2000. This pattern, is similar to that of the summer of 1989, when early summer fires followed a very dry winter and spring associated with an unusually cold episode in the tropical Pacific (La Niña). The fire-ENSO relation appears to be strongest during extreme phases of the Southern Oscillation Index (SOI). Any skill in forecasting fire hazard, however, will be constrained to roughly 30 to 35% of the annual fire variance explained by indices of the Southern Oscillation.

Synchronous large fires in the Southwest over three centuries, and their association with ENSO and the phase of the PDO, deficient spring precipitation, and reduced tree growth, imply that seasonal climate, and not just fire weather, determines burning of vegetation on a subcontinental scale.

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