Dynamics of meteorological and hydrological drought: The impact of groundwater and El Niño events on forest fires in the Amazon.

Over recent decades, anthropogenic forest fires have significantly altered vegetation dynamics in the Amazon region. While human activities primarily initiate these fires, their escalation is intricately linked to climatic conditions, particularly droughts induced by the warm El Niño phase. This study investigates the impact of meteorological and hydrological drought on forest fires in the Amazon, focusing on the role of groundwater and El Niño events. Utilizing comprehensive drought indicators at various soil depths and standardized precipitation indexes, the research spans from 2004 to 2016, revealing a consistent decrease in humidity conditions across surface soil moisture, root zone soil moisture, and groundwater storage levels. With its slower response to precipitation changes, groundwater emerges as a crucial factor influencing hydrological drought patterns in the Amazon. The spatial distribution of drought conditions is explored, highlighting areas with lower humidity concentrations in the northeast and a correlation between forest fires and positive rates of change in burned area fraction during El Niño events. Notably, the study underscores the substantial increase in burned area during the 2015-2016, characterized by a very strong El Niño. This nuanced understanding of groundwater dynamics and its interplay with El Niño events provides critical insights for developing a tailored fire risk index in the ecologically significant and vulnerable Amazon basin, subsidizing strategies for mitigating fire risk and enhancing preparedness.