Projection of future fire emissions over the contiguous US using explainable artificial intelligence and CMIP6 models
Increasing temperature and water cycle changes due to warming climate may increase wildfire activities. Reliable projections of fire emissions are critical for informing fire management to address fire impacts on societies and ecosystems. Here, we construct a neural network (NN) model explained by the Shapley Additive explanation (SHAP) to predict fire PM2.5 emissions change and understand their drivers over the contiguous US (CONUS) in the mid-21st century under a high greenhouse gas emissions scenario (SSP5-8.5). Using future meteorology and leaf area index (LAI) simulated by eight global climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), future population density, and present-day land use and land cover (LULC) as input to the NN model, the total fire PM2.5 emissions over CONUS are projected to increase by 4-75% (model spread). Among different regions, fire emissions in the western US are projected to increase more significantly in June-July-August (JJA) than in other seasons and regions, with the median ratios of future to present-day fire emissions ranging from 1.67 to 2.86. The increases in fire emissions are mainly driven by increasing normalized temperature (23-29%) and decreasing soil moisture (2-10%) in the future. When future LULC change is considered, the projected fire emissions further increase by 58%-83% over the western US compared to projections without LULC change because of future increases in vegetation fraction. The results highlight the important role of warmer temperature, decreasing soil moisture, and LULC change in increasing fire emissions in the future.