Contingent Pacific–Atlantic Ocean influence on multicentury wildfire synchrony over western North America

Abstract

Widespread synchronous wildfires driven by climatic variation, such as those that swept western North America during 1996, 2000, and 2002, can result in major environmental and societal impacts. Understanding relationships between continental-scale patterns of drought and modes of sea surface temperatures (SSTs) such as El Niñ o-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) may explain how interannual to multidecadal variability in SSTs drives fire at continental scales. We used local wildfire chronologies reconstructed from fire scars on tree rings across western North America and independent reconstructions of SST developed from tree-ring widths at other sites to examine the relationships of multicentury patterns of climate and fire synchrony. From 33,039 annually resolved fire-scar dates at 238 sites (the largest paleofire record yet assembled), we examined forest fires at regional and subcontinental scales. Since 1550 CE, drought and forest fires covaried across the West, but in a manner contingent on SST modes. During certain phases of ENSO and PDO, fire was synchronous within broad subregions and sometimes asynchronous among those regions. In contrast, fires were most commonly synchronous across the West during warm phases of the AMO. ENSO and PDO were the main drivers of high-frequency variation in fire (interannual to decadal), whereas the AMO conditionally changed the strength and spatial influence of ENSO and PDO on wildfire occurrence at multidecadal scales. A current warming trend in AMO suggests that we may expect an increase in widespread, synchronous fires across the western U.S. in coming decades.Atlantic Multidecadal Oscillation ͉ El Niñ o Southern Oscillation ͉ fire history network ͉ ocean warming ͉ Pacific Decadal Oscillation

Climate drivers of regionally synchronous fires in the inland Northwest (1651 - 1900)

“…In contrast, neither ENSO or PDO acting independently was a strong driver of fire, consistent with local-scale analyses in dry forests of the inland Northwest Hessl et al 2004;Wright and Agee 2004) and with regional-scale analysis in dry forests of the Northern Rocky Mountains just to the east, where historical fires were not strongly driven by variation in PDO (Heyerdahl et al in press). The occurrence of our highly synchronous regional fire years is consistent with climate and large-scale climate patterns across western North America (Kitzberger et al 2007). Over half (67%) of our highly synchronous fire years occurred under a northwestsouthwest dipole in summer PDSI (Fig.…”

“…However, climate drivers of fire emerge most strongly when fire chronologies are examined across broad areas (e.g. Kitzberger et al 2007), thus the lack of strong relationships between fire and ENSO or PDO at individual sites may not reflect the role of these large-scale climate parameters in synchronising fire across the region. Furthermore, none of these studies explored the role of temperature or interactions of ENSO and PDO in driving fire.…”

Fire Climatology in the western United States: introduction to special issue

“…Veblen et al 2000;Kitzberger et al 2001Kitzberger et al , 2007Heyerdahl et al 2002, in press;Swetnam and Baisan 2003;Grissino-Mayer et al 2004;Hessl et al 2004;Brown and Wu 2005;Schoennagel et al 2005;Taylor and Beaty 2005;Sibold and Veblen 2006). These studies have been enabled, in part, by the availability of independent climate reconstructions from tree-ring width and density measurements.…”

“…1) (e.g. Kitzberger et al 2007;Power et al 2008 A defining feature of the Tucson and Flagstaff workshops and the session in San Diego was inclusion of both modern and paleofire perspectives. The philosophy of this interdisciplinary approach is that integration of the unique insights from historical studies working with different data types across a range of spatial and temporal scales and resolutions can provide broader and deeper understanding of fire climatology.…”

Topography affected landscape fire history patterns in southern Arizona, USA

“…Regional analyses involving broad networks of fire-scar chronologies in the Southwest (e.g., Swetnam and Baisan, 1996;Swetnam et al, 2001), and western U.S. (Kitzberger et al, 2001(Kitzberger et al, , 2007 have produced multiple insights about long-term climate and land use controls on fire regimes. There have, however, been relatively few ''spatially explicit'' fire history investigations at landscape scales (i.e., mountain range to watersheds) in the Southwest (see Fulé et al, 2003;van Horne and Fulé , 2006;Falk and Swetnam, 2003, Farris, personal communication).…”