Change in the fire season pattern from bimodal to unimodal under climate change: The case of Daxing'anling in Northeast China
The length of the wildfire season has become longer in many regions around the world under climate change. This study investigated changes in fire season pattern (i.e., the number of separate periods of a year when wildfires are most likely to ignite, spread, and affect resources) and the contributions of climate change in Daxing'anling, Northeast China. An expanded fire dataset in both spatial and temporal converge from ground reporting was used. A comparison with satellite detected burned areas showed good agreement in spring, summer, and entire fire season. The results showed that the number of fires used to appear in a bimodal pattern with spring and fall peaks in the last century, but transitioned to a unimodal pattern peaked in summer in this century. This conversion was mainly resulted from a remarkable increase in summer lightning fires, which was in turned associated with warming in Daxing'anling. Another factor for the conversion was decreased spring nonlightning fire occurrence in the northwest subregion, where the conversion was the most significant. This decrease of fire was mainly associated with increased precipitation. The analysis of a compositional fire series, built as the log of the ratio of lightning to nonlightning fires, suggests that climate change was a major factor for the conversion of fire season pattern. The finding from this study indicates a need to adjust the fire prevention implementation timeline by including summer fires and to develop strategies to reduce the related risks to firefighter safety and forest ecosystem health in Daxing'anling.