Characterizing the climate drivers of burned area in the western US, 1984-present

Speaker:
Caroline Juang
Ph.D. Candidate, Earth and Environmental Sciences, Columbia University

In the western United States (US), area burned has increased by ~300% in four decades. Despite the large increase, much of the western US has not yet burned, leaving an abundance of fuel for future fire in a warming and drying climate. It is therefore urgent that we continue to improve our understanding of how and where climate variability and change are going to continue affecting western US wildfire. In our research, we consider a few questions: How does climate affect burned area in the western US? And how might the tropical Pacific Ocean—a dominant source of uncertainty in climate projections—affect fire-related climate variability over the western US? Using a dataset of Landsat-based and government agency-based fire events and a MODIS-based daily fire dataset, we show that the strong exponential response of annual area burned to aridity is driven by the tendency for exponential growth of individual fires, which promotes an exponential size distribution among fires. We will then demonstrate that the observed trend toward a more La Niña-like state in the tropical Pacific since the 1980s was likely a substantial contributor to the rapid increase in annual area burned, particularly in forested areas. Given the exponential response of area burned to aridity, future climate variations will amplify the range of possibilities of future fire activity relative to those of the past. We therefore propose that large uncertainties in projections of tropical Pacific sea-surface temperatures and ENSO translate to a larger range of uncertainty in future western US forest-fire activity than is currently appreciated.