PS 5-40
A recent history of disturbance: Landscape-scale patterns of fire and drought in eight High Plains states, USA
We examine 33 years (1980-2012) of temperature, precipitation and natural Federal wildfire occurrence data to determine landscape-scale patterns of drought and fire on the southern and central High Plains of the western United States under a changing climate. These High Plains states are in the midst of ongoing extreme drought, experiencing below normal precipitation and above normal temperatures for the past several years. Drought is expected to persist or intensify. In addition, climate change is predicted to have multiple effects on fire regimes. Our goal is to relate the frequency and size of wildfires to a precipitation, temperature and latitudinal gradient to increase understanding of fire and drought interactions on the Great Plains in the face of climate change. Annual and seasonal climate trends were quantified between 1980 and 2012 for the High Plains EPA Ecoregion using the temporal Parameter-elevation Regressions on Independent Slopes Model (PRISM) climate model datasets. Linear trends were fitted to each pixel to develop the slope, or rate of change through time for annual average precipitation, minimum, maximum, and average temperature. Changes in fire frequency and size were tested with Poisson and normal GEE models respectively including autoregressive errors and offsets for exposed land by state.
Results/Conclusions
Preliminary results indicate average annual precipitation decreased across the High Plains study area by 2.8 mm yr-1(+/- 1.3 mm), and was especially pronounced during the period of June, July and August. Annual average maximum temperature increased by 0.03° C yr-1(+/- 0.015 °C), while minimum and average temperatures remained relatively unchanged. Approximately 61,000 natural wildfires on Federal and Tribal lands occurred in the 8 states from 1980 to 2012 (roughly 10% were High Plains wildfires). Overall there was a significant increase in number of fires from 1980 until circa 2005. After 2005 there was a slight decrease or leveling off in the number of fires. Total acres burned increased until 1991-92, and then acres burned plateaued until 2007, when it began to increase again. On average there does appear to be a significant increase in total acres burned over the entire 33 years. Results point to trends in reduced precipitation and increased temperatures, with more and larger fires in the region over the last three decades. Our results will be used to improve predictive forecasts of fire in the Great Plains, which are currently prone to uncertainties related to climate projections and a paucity of information on grassland fire-climate relationships.