Century-scale climate forcing of fire regimes in the American Southwest

Interannual time-scale associations between fire occurrence and drought ind ices, the Southern Oscillation, and other synoptic patterns demonstrate tha t large-scale, long-term atmospheric features are precursors to regional fi re activity. However, our knowledge of fire-climate relations over longer ( century) timescales is fragmentary because of the rarity of comparable clim ate and fire time-series with sufficient resolution, length and regional ex tent. In this study, we develop reconstructions of wildfire occurrence from tree-ring data collected from northwestern New Mexico to compare with a mi llennium-length dendroclimatic reconstruction of precipitation. Reconstruct ions of both wildfires and climate show simultaneous changes since AD 1700 that indicate climate forcing of wildfire regimes on interannual to century timescales. Following a centuries-long dry period with high fire frequency (c. AD 1400-1790), annual precipitation increased, fire frequency decrease d, and the season of fire shifted from predominantly midsummer to late spri ng. We hypothesize that these shifts in fire regimes reflect long-term chan ges in rainfall patterns associated with changes in synoptic-scale atmosphe ric circulation patterns and the Southern Oscillation. Our evidence support s century-scale climate forcing of fire regimes in the American Southwest, providing a useful analogue of future wildfire regimes expected under chang ing global climate conditions.