Igniting lightning, wildfire occurrence, and precipitation in the boreal forest of northeast China

Cloud-to-ground (CG) lightning is the primary cause of major boreal forest wildfires. Characterizing igniting lightning and the weather conditions favoring ignition is essential for wildfire prediction and prevention. However, these studies have not been conducted in the Greater Khingan Mountains of northeast China, the region with the largest boreal forest and the most frequent lightning-induced fires in China. The newly established three-dimensional lightning position network and high-resolution precipitation product spanning 2019–2021 were used to identify and characterize the igniting lightning, and explore the impacts of precipitation and lightning on ignition probability at different spatio-temporal scales. Igniting lightning was identified by the maximum proximity in time and distance to lightning fires. Around 80 % of lightning fires occurred within 24 h and a 1 km radius of the igniting lightning. The short holdover time could arise from intense solar heating, low fuel moisture, and frequent lightning activity in the afternoon. CG lightning density in a 1 km radius around the reported fire points was much higher than the outer buffer zones within the previous 24 h, affirming the high spatio-temporal accuracies of lightning fire and CG lightning data. The seasonal and diurnal distributions of lightning fires were modulated by CG lightning frequency variations. Although lightning characteristics played a role, precipitation is the predominant factor controlling both the spatial pattern of lightning fires and ignition probability. Fewer precipitation intensities, both preceding and following CG lightning, matter for ignition. The most prominent precipitation difference was observed 4 h prior to 4 h following igniting and non-igniting lightning, when the precipitation intensity was less than 0.5 mm/hour for igniting lightning.