Resilience across the Amazon basin regions under increased drought frequency and severity
Authors: Rius Bianca , Cardeli Barbara , Blanco Carolina , Darela Filho João Paulo , Hirota Marina , Lapola David 
Published: March 2024

The anticipated rise in the frequency of severe droughts triggered by events such as El Ni&#241;o and abnormal warming of the Atlantic Ocean is expected to have profound impacts on the Amazon forest. However, whether the Amazon forest can effectively cope with changes in precipitation patterns and maintain its resilience remains to be determined. The impacts can vary across different regions of the Amazon due to the inherent heterogeneity in annual precipitation rate and periodicity in dry and wet periods. Furthermore, it is essential to highlight that resilience assessment frequently revolves around the ecosystem's ability to maintain or restore its carbon stock after a disturbance. Nonetheless, numerous other ecosystem processes and properties, such as evapotranspiration and functional diversity, might signal a shift in resilience before a consistent alteration in carbon stock becomes apparent. To address these concerns, our study will apply the trait-based vegetation model CAET&#202; (CArbon and Ecosystem functional Trait Evaluation model). To comprehend the effects of an elevated frequency of decreased precipitation in the Amazon forest, we will apply a 20% precipitation reduction across three different frequencies: 7 years, 3 years, and 1 year. The model will be run across five distinct Amazon regions: northwest, center, south, northeast, and southeast. The assessment of resilience will encompass both resistance and recovery measures and will be evaluated using standard metrics such as carbon stock, while the analysis will extend to include other crucial indicators such as evapotranspiration, net primary productivity, and functional diversity. We anticipate uncovering differences in resilience among the regions, primarily influenced by natural climatic heterogeneity that selects distinct compositions of functional traits, leading to varying levels of functional diversity. Our hypothesis suggests that initially, the northwest region may experience a buffering effect from its naturally high precipitation rate. This could potentially result in more subtle impacts, even in the face of reduced precipitation. However, over time, other regions may demonstrate greater resilience, as their communities might show functional strategies acclimated to prolonged dry conditions and lower precipitation rates. Additionally, we also expect to observe a prior decrease in evapotranspiration and functional diversity before the eventual collapse of carbon stock and net primary productivity. This expectation is rooted in the anticipated intensification of environmental filtering, wherein the ecosystem undergoes a process of selecting more conservative adaptive strategies to deal with drier climatic conditions. By employing this innovative approach to assess resilience, incorporating diverse indicators beyond solely relying on carbon stock, we aim to significantly improve the understanding of Amazonian ecosystem dynamics under changing climatic conditions. Ultimately, our findings may unveil that the Amazon forests are potentially more susceptible to environmental changes than previously envisioned.