The Role of Moisture and Heat Transport for Extreme Droughts in the Amazon Basin - a Lagrangian Perspective

Abstract

In the last decade, tropical rainforests, e.g. the Amazon basin, have experienced events of extreme droughts. Such events have huge impacts on the forest, as trees are damaged. Therefore, it is relevant to gain deeper understanding on the main mechanisms causing such events, and further clarify the role of moisture recycling over the continent vs. moisture transport from oceanic regions.We study the role of moisture- and heat transport for the Amazon basin, with special focus on drought events. We show how these extreme events differ from normal conditions, with special focus on the changes in atmospheric transport. We analyse the atmospheric transport with the particle dispersion model FLEXPART using meteorological input data from the ERA5 reanalysis. In this Lagrangian model, the atmosphere was filled homogeneously with particles, which were traced forward in time and represent the global atmospheric mass transport. From this Lagrangian reanalysis dataset, covering the years 1979-2021, air masses over the Amazon basin are selected and traced backward in time. Based on that, we investigate the role of continental and oceanic moisture source areas, incorporating also information on soil moisture and burned areas. Thereby, we highlight the relevance of moisture recycling over continental - vs.  moisture transport from oceanic areas. For example, we found that for the northern parts of the Amazon basin the most important moisture source is the Atlantic Ocean, thus this area is less affected by deforestation in the southern areas.