Much more wildfire burns in the West during years with early snowmelt

Anthony Westerling and colleagues studied western US wildfires and how they were affected by variations in snowmelt timing from 1970 – 2003. [[Westerling, A. L., H. G. Hidalgo, D. R. Cayan, and T. W. Swetnam. “Warming and earlier spring increase western US forest wildfire activity.” (PDF) Science 313, no. 5789 (2006): 940–943.]] They divided the period into the 11 earliest melt years, the 11 latest, and 12 “normal” years. One result: across the West, while 72% of the land that burned during the entire study period burned during the early snowmelt years, just 4% burned during the late melt years. And about five times as many wildfires burned during the early-melt years than the late-melt years. Early snowmelt can lead to drier soil and vegetation, putting forests at higher risk of burning. And, in fact, the average timing of snowmelt has been getting earlier in the American West in recent decades, a trend linked to climate warming in the region[[ Barnett, T. P., D. W. Pierce, H. G. Hidalgo, C. Bonfils, B. D. Santer,T. Das, G. Bala, A. W. Wood, T. Nozawa, A. A. Mirin, D. R. Cayan, M. D. Dettinger: “Human-Induced Changes in the Hydrology of the Western United States” (Abstract) Science, 329, 2008 pp. 1080-1083.]] [[Hidalgo, H.G., T. Das, M.D. Dettinger, D.R. Cayan, D.W. Pierce, T.P. Barnett, G. Bala, A. Mirin, A.W. Wood, C. Bonfils, B.D. Santer, and T. Nozawa: Detection and Attribution of Streamflow Timing Changes to Climate Change in the Western United States.” (Abstract) J. Climate, 22, 2009. 3838–3855.]] and longer fire seasons.

Westerling and his colleagues used measurements of the timing of snowmelt obtained by US Geological Survey data on water flow in streams fed mainly by melting snow. They developed their own dataset of large wildfires, from a variety of sources.