Fuel availability versus flammability: divergent fire controls across Eurasian drylands.

Fire regulates the carbon, water and nutrient cycles, especially in regions with distinct wet and dry seasons. The dramatic vegetation response to climatic factors complicates fire preconditions in Eurasian drylands, leaving our understanding of climate-fuel-fire patterns limited. Here we identify eight pyromes with unique combinations of fire characteristics of size, expansion, frequency and duration. We find these pyromes are geographically contiguous and exhibit varied response to climate, fuel load, fuel flammability and human activities. Fuel load is closely related to fast-spreading fires in Eurasian Steppe, which mostly belongs to the large-fast-frequent-long (LFFL) and medium-fast-intermediate-short (MFIS) pyromes. There, antecedent fine fuel accumulation during the growing season dries out in the subsequent dry season, is ignited by human activity and spreads rapidly. High-latitude regions are dominated by slow-spreading but long-lasting fires (large-slow-rare-long (LSRL) and medium-slow-intermediate-long (MSIL) pyromes), where changes in fuel flammability due to long-term climate stress determine fire extent. These findings provide initial guidance of which controls should be considered for improving predictions of fire activity and fire risk assessment across Eurasian drylands.