Laboratory of Tree-Ring Research and School of Natural Resources and the Environment

Understanding the role of climate variation in governing fire regimes remains one of the central needs in contemporary fire science and management. Ideally, this understanding should encompass both historical and current fire-climatology, and inform both basic science and ecosystem management. In this project, Fire and Climate Synthesis (FACS) we undertook a detailed synthesis of both paleofire and modern fire based on compilations of existing data sets. We also analyzed three major thematic pathways by which climate has impacted fire policy, including direct and indirect climate effects on fire policy. Paleofire. We assembled the largest and most comprehensive data set of cross-dated, georeferenced fire-scar paleofire records ever compiled for western North America. Data were provided by over 60 researchers in the field, in the form of data files, published reports, and individual study records. We also accessed the most recent holdings of the International Multiproxy Paleofire Database (IMPD) for inclusion in our compilation. These efforts resulted in the compilation of 1,248 fire history studies from 64 contributors meeting our quality criteria. Study locations extend from southern Canada to north-central Mexico, and cover the 3,248-yr period 1248 BCE to 2011 CE, with sample size > 600 sites covering the period 1700-1990. Seven major forest types are represented, including pinon-juniper, pine-oak woodland, ponderosa pine woodland, dry and mesic mixed conifer, fir, and subalpine forests. Mean annual precipitation ranges from  30 cm to  200 cm, while mean annual temperature ranges from 5.0 to 25.3 °C. We identified numerous west-wide fire years in the paleofire record indicating the strong top-down influence of synoptic climate conditions and regulation by major climate oscillatory modes. Our work included the development of new software tools to facilitate future analyses of paleofire data sets (see Decision Support Tools, below). Modern fire. For our synthesis of modern fire-climatology, we focused on analyzing trends and drivers in area burned in western forests, particularly the influence of snowpack duration and climate variables to annual area burned. We compiled annual area burned (AAB) for the western US based on data provide by Dr. AH Westerling, University of California – Merced, for the period 1972-2006. 12,596 fires met data quality standards and were included in analysis. Similar data were obtained from the Canadian Large Fire Database. Spatiotemporal climate layers (monthly mean, minimum, and maximum temperature and precipitation) were obtained from the National Climate Data Center for the same time period. We obtained snowpack data estimating the presence or absence of snowpack from satellite reflectance data aggregated to 25 km2 pixels. Snowpack data were converted to a continuous variable, LDPS (Last Date of Permanent Snowpack). We evaluated all time series for trend over the period of analysis at the scale of each 1° grid cell. For AAB we analyzed the period 1972-1999, and climate variables and snowpack for the period 1972-2006. To separate the influence of multiple drivers, we employed path analysis to identify the relative contributions of seasonalized temperature, precipitation, and snowpack duration to AAB. AAB increased significantly over most of the study area during the period 1972-1999. Seasonalized temperatures increased, and winter precipitation and snow cover duration decreased, over most of the study area significantly over the period of analysis (1972-2006). Winter temperature and precipitation had the strongest effect on snowpack duration. In turn, snowpack duration affected AAB, but results were spatially heterogeneous. Overall, the strongest effects on AAB were the direct effects of winter and temperature, followed by direct effects of spring precipitation. Most indirect effects, i.e. University of Arizona, Final Report, Fire and Climate Synthesis, JFSP 09-2-01-10, p. 3 mediated by climate effects on snowpack, were a relatively small component of variability. Effects of snowpack on AAB were spatially variable in strength and sign. These results suggest that snowpack duration may be an indicator of the factors that control AAB, rather than a mechanism of control. We also compiled the first complete set of “pyroclimographs” for the western US, visualizations that integrate monthly mean temperature, precipitation, and area burned from both lightningand human-caused fires. Influence of climate change on fire policy. The objectives of this component of the synthesis were to reconstruct and synthesize the pathways by which past climate‐fire events have shaped policy and decision‐support systems for national wildland fire management, and to determine ways to proactively use climate change and fire/climate relationship knowledge to inform to policy and guide decision‐support systems. We collated information from a wide range of published sources, Incident Reports, current and recent wildland fire policy documentation, peer-reviewed manuscripts, technical reports and other gray literature, and essays and articles on fire management history in the US, including previous syntheses of fire policy history. We also held informal discussions with five national level fire program managers who shared a combined experience of over 150 years in fire management across four of the five primary federal land management agencies. We also reviewed curricula for 15 different courses taught at the National Advanced Fire and Resource Institute (NAFRI). From our literature review and our discussions, we identified two types of climate impacts on fire policy: direct (top-down) and indirect (bottomup). For each impact type, we identified events, trends, and resulting policy or changes in management. Deliverables from this section of the project include an analysis of climate impacts on US national wildfire policy and practice in the form of webinars and published journal papers. Decision Support Tools. The technology transfer tools developed from this project include workshops, webinars, publications, analytical tools, presentations, and fact sheets. We also developed several new software applications that facilitate fire history analysis, including Java-based tools for superposed epoch analysis, fire history file combination, and for generating binary output files used for fire history statistical analyses. University of Arizona, Final Report, Fire and Climate Synthesis, JFSP 09-2-01-10, p. 4 BACKGROUND AND PURPOSE A recent wave of scientific publications and interest in fire climatology derives in part from two new paradigms in climatology: (1) the discovery and understanding of broad-scale ocean-atmosphere oscillations (e.g., El Nino-Southern Oscillation, Pacific Decadal Oscillation, and others) and their teleconnections to regional and continental temperature, precipitation and fire regimes, and (2) the mounting evidence of secular warming trends occurring at local to global scales that are largely driven by increasing greenhouse gases in the atmosphere, and concurrent increases in areas burned and the length of fire seasons. In addition to these developments, fire and climate history datasets have greatly expanded and improved in the past decade. The increased availability of these datasets has facilitated a substantial increase in the literature of fire climatology encompassing both “paleo” (i.e., pre 1900) and modern time periods, especially for the western United States and Canada. Although many new insights have been gained, until recently there has been no synthetic review of western U.S. fire climatology to date. Nor is there a clear and comprehensive regionalization (from the literature and data) of fireclimate patterns, teleconnections, lagging relationships, etc., or evaluation of unknowns and limitations of fire climatology. Furthermore, we are in the early developmental stages of facilitating access to and use of fire history and fire climatology information by managers and policy makers (e.g., “Predictive Services” products). We also have much to learn from past fireclimate events and management/policy responses. We designed and carried out the Fire and Climate Synthesis (FACS) project for western North America fulfilling the needs of syntheses, improved data access and communication, and learning from past management experiences and policy evolution. In particular, we proposed to: (1) Conduct a quantitative synthesis of paleo and modern fire and climate history time series to define a “geography of fire climatology” of the western U.S.; (2) incorporate the fire-climate synthesis results into a set of existing management decision support tools, to inform managers and decision makers about relationships between climate and fire under past, present, and potential future climate regimes; and (3) conduct a series of workshops and interviews with fire managers to define and explore the applications of fire climatology in fire management (especially resource allocation, appropriate management response, and fuels treatments), and to learn from past management responses to fire-climate events, and the resulting policy changes. STUDY DESCRIPTION AND LOCATION The spatial scope of the FACS project is the western United States. Additional information has been incorporated from southwestern and central Canada and northern Mexico.