From droughts to river erosion: compound hazards in the Central Amazon

The Central Amazon has been facing an increase in extreme events in the last decades, including droughts, floods, heatwaves, erosion and fires. Here we summarize a series of recent studies where we describe the compound nature of several of these events, based on field data collection of environmental, social and ecological variables, as well as satellite data. We describe the simultaneous occurrence of drought, river erosion and sediment deposition, air and water heatwaves, fires and phytoplankton blooms that occurred during the recent 2023 and 2024 record-breaking droughts. The social-ecological impacts associated with these events include challenges on the management of natural resources (fisheries, agriculture, timber extraction) and access to goods and services in riverine communities, as well as mortality of aquatic animals and general alteration of natural ecosystems. Major heatwaves took place in Amazon lakes in 2023 and 2024, leading to water temperatures as high as 41°C and mortality of dolphins and fish, such as in lakes Tefé and Coari. One particular phenomenon associated with sediment-laden Amazon rivers is the periodic migration of river meanders, which leads to major erosion over communities, with deaths and infrastructure destruction, as well as deposition of sediments on the opposite river bend, leading to isolation of communities during major droughts. Besides droughts and associated compound events, recent intensification of floods is also occurring, with the 2021 flood being the largest one ever recorded in more than 120 years of measurements in the Negro River at Manaus. This long-term increase in floods has increased flood duration, extent and river-floodplain connectivity in several portions of the Amazon mainstem, severely impacting social-ecological systems, although to a lesser extent than droughts and associated events. Overall, the impacts of such extreme events on Amazon people and ecosystems are still poorly understood and represented in regional to national disaster databases, and there are major limitations in current public policies to deal with risk and disaster management. There is a huge need to improve local monitoring networks of social and ecological processes, as well as the physical environment.