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STUDY. From Science Advances magazine August 8th, 2025, by Gavin D. Madakumbura, Max A. Moritz, Karen A. McKinnon, A. Park Williams, Stefan Rahimi, Benjamin Bass, Jesse Norris, Rong Fu, Alex Hall.
𝗔𝗻𝘁𝗵𝗿𝗼𝗽𝗼𝗴𝗲𝗻𝗶𝗰 𝘄𝗮𝗿𝗺𝗶𝗻𝗴 𝗱𝗿𝗶𝘃𝗲𝘀 𝗲𝗮𝗿𝗹𝗶𝗲𝗿 𝘄𝗶𝗹𝗱𝗳𝗶𝗿𝗲 𝘀𝗲𝗮𝘀𝗼𝗻 𝗼𝗻𝘀𝗲𝘁 𝗶𝗻 𝗖𝗮𝗹𝗶𝗳𝗼𝗿𝗻𝗶𝗮
In this study, we investigate changes in fire season onset across the ecoregions in California, using an extensive record of fire occurrence data from 1992 to 2020 (25). By analyzing the distribution of recorded fire start dates, we establish a physically interpretable definition of fire season onset. To diagnose the causes of the observed trends in onset, we (i) consider the potential roles of nonclimate factors such as fuel types and ignitions and (ii) provide a detailed decomposition and quantification of climate drivers, distinguishing between natural variability and anthropogenic warming.
Drivers of an earlier fire onset
Fire onset trends toward an earlier fire season can be theoretically driven mainly by three elements that could increase the number of fires and therefore shift or stretch the distribution of fires earlier in the year (fig. S1): (i) increased fuel loads due to, for example, fuel accumulation (31), (ii) increased frequency of human-ignited fires, which tend to occur more year-round than lightning-ignited fires (32, 33), and (iii) climate trends such as reduced cool-season precipitation, atmospheric warming, and early snowmelt, which promote the drying of fuels earlier in the year (23). We investigate each of these potential drivers to understand their effects.
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Author: mdrag
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