The Role of Lightning in Simulations of the Spatiotemporal Distribution of Global Fire

Fire is a major disturbance in terrestrial ecosystems and a large source of carbon to the atmosphere. Meteorology and human activities combine to shape the spatiotemporal distribution of fires. The fundamental meteorological state, however, is projected to change as fossil fuel carbon continues to accumulate in the atmosphere. These changes will create conditions that are more conducive to fire occurrence. Compounded with the complexities that the impacts of changing climate will have on fire regimes is the projected increase in human population and, therefore, additional human ignition sources. Thus, the fundamental drivers of global fires are in a state of flux, and because these drivers of fire distributions are key elements of global fire models, the scientific study of the relationship between fires, climate, and humans is rapidly evolving.

While humans are the ignition source of the vast majority of fires on Earth, lightning plays a significant role in triggering fires in some regions. Preliminary results from our global fire model suggest that about 10% of non-agricultural burned area is caused by lightning-triggered fires. The fraction of fires that is caused by lightning is considerably different at the regional scale. Namely, our model output suggests lightning is responsible for 20-30% of fires in Canada, northern Russia, and Australia and 10-15% in the United States and South America. In terms of absolute magnitude, Southern Africa and Australia account for the largest number of lightning-caused fires. The number of fires is expected to increases globally as climate changes and human population increases, but the role of lightning in terms of either interannual variability or long-term changes has not been strongly considered in global fire models. Regions such as the boreal forests of Canada and Russia are particularly interesting because there is a tremendous amount of carbon stored in the land component of the biosphere and the same regions may experience relatively larger changes in climate. Most likely, the human role in fire occurrence in these regions will not change as fast as the meteorological state.

In this presentation, I will discuss formulations behind our effort to model global fires with a focus on aspects of the model we look to improve upon with respect to the simulation of lightning-triggered fires. I will also discuss the limitations in our current approach. The main point of my presentation is then to present global lightning distributions from the perspective of global fire modeling.