Abstract
Red Flag Warnings (RFWs) issued by the National Weather Service in the United States (U.S.) are an important early warning system for fire potential based on forecasts of critical fire weather that promote increased fire activity, including the occurrence of large fires. However, verification of RFWs as they relate to fire activity is lacking, thereby limiting means to improve forecasts as well as increase value for end users. We evaluated the efficacy of RFWs as forecasts of large fire occurrence for the Northwestern U.S.—RFWs were shown to have widespread significant skill and yielded an overall 124% relative improvement in forecasting large fire occurrences than a reference forecast. We further demonstrate that the skill of RFWs is significantly higher for lightning-ignited large fires than for human-ignited fires and for forecasts issued during periods of high fuel dryness than those issued in the absence of high fuel dryness. The results of this first verification study of RFWs related to actualized fire activity lay the groundwork for future efforts towards improving the relevance and usefulness of RFWs and other fire early warning systems to better serve the fire community and public.
Highlights
Wildland fire plays an important role as a natural and increasingly anthropogenic disturbance found in most vegetated ecosystems globally [1,2] and generally serves to promote healthy, resilient landscapes [3]
While some studies have shown the importance of meteorological conditions tied with Red Flag Warnings (RFWs) criteria on fire activity [32], this study provides a first known effort to evaluate the added value of RFW forecasts for actualized large fires (LFs) activity that is of key importance for fire suppression
We found the skills of RFWs for meaningful measurements of fire activity broadly across the Northwestern U.S We demonstrated that RFW skill was significantly better for lightning-caused LF days (LFDs) and when issued coincident to high fuel dryness
Summary
Wildland fire plays an important role as a natural and increasingly anthropogenic disturbance found in most vegetated ecosystems globally [1,2] and generally serves to promote healthy, resilient landscapes [3]. Longer periods of critical fire weather [7] coupled with human-caused fire activity [8] and increased fuel loads as a result of fire suppression activities [9] have expanded the threat of hazardous fires in the United States (U.S.), making land management objectives more difficult and costlier to achieve, while placing the safety of fire suppression personnel and the public at greater risk These effects have been demonstrated by recent fire events in the U.S [10,11,12] and are expected to continue due to anthropogenic climate change [4,13] and the growth of wildland–urban interfaces [14]. Comprehensive fire danger systems integrate weather, fuels, Fire 2020, 3, 60; doi:10.3390/fire3040060 www.mdpi.com/journal/fire
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