Abstract:

Wildfires triggered by lightning have caused significant losses of ecology, property and life worldwide. With climate warming and El Nino phenomena, there has been a significant increase in the activity of thunderstorms and lightning around the world, and the area burned by lightning-caused fires has increased significantly. However, at present, there is still a big knowledge gap in the research on the lightning ignition process and mechanism. In this paper, we summarized the rule of lightning, factors affecting lightning density and the pattern of lightning days in China, made a link between the occurrence and prediction of lightning-caused fires, and explored the relationship between the pattern of lightning and lightning-caused fires. The lightning occurrence has the characteristics of randomness and instantaneity in time, and the characteristics of lightning are different in different regions. The lightning density is higher in the east than in the west, in the south than in the north, and on the land than in the sea. Lightning-caused fires in the forest are caused by the thermal effect of cloud-ground lightning current. Ignition or not is closely related to the polarity and current intensity of lightning. Lightning density is also affected by altitude, vegetation distribution, soil type, topography and burned area. Higher elevations cause forced convection, which leads to lightning strikes. Woodland, shrub and grassland have different lightning strike densities due to different surface heating levels. Large burned areas cause lightning strikes through enhanced free convection or mesoscale circulation; and the areas strongly influenced by human activities (such as urban, mining, and industrial) have more lightning activity. Fluvisols, cambic-arenosols and luvisols are associated with increased lightning activity. The cumulus clouds generated by forest fires may also trigger another fire. The mean thunderstorm duration in the region east of 105°E increases with decreasing latitude. The process of lightning-induced lightning fires includes three stages: discharge heating stage, thermal feedback stage and spontaneous flame stage. Moreover, climate change can affect the occurrence and ignition probability of lightning. In the future, the increase of lightning occurrence and ignition probability will largely lead to the increase of fire risk in space and time. At present, lightning prediction models often do not rigorously assess the occurrence of lightning. Measurement systems to detect long-term trends in lightning should be developed in the future. By means of satellite communication, UAV, atmospheric electric field measuring system, combined with artificially triggered lightning technique and field ignition experiment, the intelligent forecast models of lightning-caused fires should be established to improve the accuracy of the probability forecast of lightning-caused fires in China, and realize the effective prevention and control of lightning-caused fires.

Key words: lightning-caused fire, thunderstorm day, cloud-to-ground lightning, ignition mechanism, climate change