Observed increases in extreme fire weather driven by atmospheric humidity and temperature

Recent increases in regional wildfire activity have been linked to climate change. Here, we analyse trends in observed global extreme fire weather and their meteorological drivers from 1979 to 2020 using the ERA5 reanalysis. Trends in annual extreme (95th percentile) values of the fire weather index (FWI95), initial spread index (ISI95) and vapour pressure deficit (VPD95) varied regionally, with global increases in mean values of 14, 12 and 12%, respectively. Significant increases occurred over a quarter to almost half of the global burnable land mass. Decreasing relative humidity was a driver of over three-quarters of significant increases in FWI95 and ISI95, while increasing temperature was a driver for 40% of significant trends. Trends in VPD95 were predominantly associated with increasing temperature. These trends are likely to continue, as climate change projections suggest global decreases in relative humidity and increases in temperature that may increase future fire risk where fuels remain abundant. Climate change has led to increased fire activity in parts of the globe due to observed increases in fire weather extremes. These trends are driven predominantly by decreasing relative humidity and increasing temperature.