Worsening Drought and the Bleak Future for Biodiversity and Ecosystem Services in the Amazon Basin

The Amazon River basin is home to one of the most biodiverse ecosystems on Earth, including countless species of many branches of the tree of life (Lapola et al. 2023). It also critically regulates regional, continental, and global climate and water cycles (Lovejoy and Nobre 2018). The Amazon's ecosystem follows a monomodal flood pulse, with annual floods and dry periods causing water level fluctuations of around 10 m (Correa et al. 2022). During high-water periods, floodplains are inundated, connecting aquatic ecosystems, while only terra firme areas stay dry, covering 14% of the basin (Correa et al. 2022; Junk 2005). In the low-water period, water is confined to the main channel, shrinking floodplain lakes and drying floodable forests. However, abnormal hydrological regimes (i.e., extreme floods and droughts) are becoming recurrent. During October 2024, historical minimum water levels were recorded in the Solimões, Negro and Madeira Rivers (Figure 1), with sandbanks and rocks becoming exposed in areas typically submerged (Mezzofiore and Gianluca 2024). This drought has left many Indigenous, quilombola and riverine communities isolated, impairing their fishing activities and struggling with food and water shortages (Kelly 2024). These unprecedented conditions mark a possible critical shift for the environment, and the Indigenous, quilombola and riverine communities, whose survival depends on the seasonal flood pulse natural cycle, face a growing threat to their food security, with the possibility of famine becoming real shortly. Drought is not an entirely new phenomenon in the Amazon basin. However, the frequency (2005, 2010, 2015, 2016, 2020, 2023 and 2024) of extreme droughts has become greater (Figure 1) (Kelly 2024; Marengo et al. 2008; Tavares et al. 2023). Each of these droughts has broken historical records in magnitude and intensity. This trend continued into 2024 and is being driven by a combination of global climate change, which may disrupt the water cycle in the Amazon basin, aggravated by El Niño conditions (Chen et al. 2024). Deforestation in the Amazon reduces tree cover, disrupting rainfall patterns and weakening water storage (Haddad et al. 2024). This trend threatens biodiversity and local livelihoods (Chen et al. 2024). The 2024 drought has lowered the water levels in the entire Amazon basin and triggered a cascade of ecological, social and economic impacts (Figure 2). Among the most critical of these impacts is the threat to the local biodiversity, which has developed over millennia to thrive in a balanced aquatic and terrestrial environment. The river's seasonal flood pulses have historically created a dynamic and heterogeneous environment that promotes biodiversity, providing habitats for a wide range of species that are adapted to move longitudinally but also laterally into the forest (Correa et al. 2022). The flood pulse usually facilitates nutrient transfer between aquatic and terrestrial zones, but drought disrupts this process. For example, fish depend heavily on terrestrial food sources like floodplain fruits, flowers, insects and seeds (Junk 2005). Without regular flooding, these resources become inaccessible, causing nutrient shortages that may lower their physiological condition and reproductive success, weakening fish populations and destabilizing the ecosystem's food web (Correa et al. 2022). In addition, migratory fish species, dependent on the flood pulse to complete their life cycles, now face habitat loss and fragmentation, forcing them into smaller pools and being more exposed to predation, competition and disease (Marengo et al. 2024). Numerous studies on recent Amazon droughts have documented massive fish mortalities during extremely dry periods, including in 2024 (Braz-Mota and Luis Val 2024; Röpke et al. 2022). In some regions, dissolved oxygen levels dropped below 2 mg L−1—a critical threshold for fish survival—resulting in the death of up to 90% of fish populations in certain floodplain lakes (Braz-Mota and Luis Val 2024). This has also had consequences for the Amazon River dolphin (Inia geoffrensis), with over 100 individuals dying in 2023, likely due to low water levels, high temperatures, reduced oxygen and decreased fish populations amid drought conditions (de Santos Lima et al. 2024). Furthermore, drought-induced lentic environments, such as pools, may enhance mercury methylation. As Gerson et al. (2020) demonstrated with artificial mining ponds, these stagnant conditions can increase mercury bioavailability and accumulation risks in aquatic ecosystems. Lower water levels also disturb sediments where mercury is stored, releasing it back into the water column, entering the food web and posing significant risks to wildlife and human health (da Costa et al. 2022). Indigenous, quilombola and riverine communities, which heavily reliant on fish as a dietary staple, now face increased risks of mercury poisoning, which can lead to neurological and developmental disorders (Soares et al. 2024). Moreover, biogeochemical changes during extreme droughts can affect the carbon cycle. For example, when water levels drop, herbaceous plants quickly grow on exposed sediments and rapidly decompose upon reflooding, releasing significant CO₂ into the water column, as observed in Janauacá Lakem, Amazon, during the 2015 drought (Figure 1c) (Amaral et al. 2022). The impacts of the drought are not limited to aquatic species. Many terrestrial animals that rely on rivers and surrounding floodplains for food and shelter are also being affected. Birds, amphibians, reptiles and mammals that depend on fish and other aquatic organisms for food are facing shortages as the river's banks dry out (Ferrante et al. 2023). Amphibians, highly sensitive to temperature and moisture changes, may be particularly vulnerable. For example, in the central Amazon, populations of common frogs like Atelopus manauensis are already declining due to shifts in temperature and precipitation linked to climate change (Jorge et al. 2020). As droughts become more frequent and intense, the availability of temporary pools formed during the rainy season is shrinking, threatening their survival (Ferrante et al. 2023). This possible decline in amphibian populations could have cascading effects throughout the food web, as amphibians are important prey for many other species. Similarly, birds, such as herons and kingfishers, struggle to find enough to eat as fish populations decline (Terborgh and Davenport 2021). Migratory birds that use the Amazon basin as a stopover during their long journeys face challenges, as drying wetlands and reduced food availability hinder their survival and migration (Bauer and Hoye 2014). Approximately 17% of Amazonian tree diversity, adapted to floodplain environments, is under stress due to dropping water tables, causing many trees to die or fail to produce seeds and fruits (Flores et al. 2024). The loss of these forests could have long-term consequences for the region's biodiversity with cascading effects at all levels of the food web organization (Flores et al. 2024). The Amazon basin provides a vast array of ecosystem services. Humans have used these rivers for a myriad of activities and particularly affected may be traditional Amazonian communities who depend on the forest's natural resources for food, water, energy, medicine and materials (Begossi et al. 2018). Those extreme droughts have severely limited access to these resources, leading to food and water insecurity (Figure 2). The drought has led to reduced water availability. Personal observations from our team gathered during fieldwork with Amazonian communities revealed that many locals rely on well water for drinking and cooking, which has become scarce as wells dry up due to the drought. Additionally, residents with piped water from river-based float systems have had to relocate these floats to the river's main channel, where water levels are higher, resulting in the loss of access to their home water supplies. In addition, fishing, a primary source of food and income for many traditional Amazonian communities, has become increasingly difficult as fish populations decline (Röpke et al. 2022). Field observations gathered by our team indicate that fishers face added difficulties and costs, including spending more money on fuel due to longer navigation routes and repairs for damage from grounding or propeller breakage as rivers dry up. Fish provide up to 70% of the protein intake in the diets of many Amazonian communities (Begossi et al. 2018). This food crisis could drive migration to urban areas and lead to economic hardship, with the risk of malnutrition, increased inequality and potential social conflicts (Mojeed et al. 2024). The environmental changes are also impacting local crops production, essential for community subsistence. Traditional farming systems, adapted to Amazon's seasonal floods, are now struggling, pushing communities toward severe food insecurity (Lapola et al. 2018). Research on the Solimões River basin highlights the importance of traditional knowledge for sustainable resource management. Traditional methods have often been more effective than Western ones for local crops (Forsberg 2018). However, there is concern that these practices may not adapt to extreme droughts (Forsberg 2018). The drought also impacts energy provision. Hydroelectric production has reportedly dropped significantly during the drought due to low water levels in the rivers that supply the plants (de Santos Lima et al. 2024). This reduction in energy generation directly affects urban areas like Manaus, which rely on locally and regionally generated electricity. Supporting and regulating services like nutrient cycling and soil formation are also being heavily impacted by the prolonged drought. The seasonal floods of the Amazon play a crucial role in depositing nutrients that support both terrestrial and aquatic ecosystems (Herrera-R et al. 2024). With more prolonged and severe droughts, the nutrient input is severely diminished, affecting soil fertility and reducing the productivity of both natural ecosystems and agricultural lands, threatening both food production and biodiversity (Tavares et al. 2023). Furthermore, the increased incidence of forest fires, which often accompany drought conditions, has significantly worsened air quality, contributing to a rise in respiratory illnesses, particularly among vulnerable populations such as children and the elderly (de Oliveira et al. 2023). Data from the Brazilian National Institute for Space Research (INPE) and the Ministry of Health (2024) indicate that hospital admissions for respiratory issues in Amazonian states increased by approximately 20% during periods of intense fires compared to previous years. For Indigenous, quilombola and riverine communities, the Amazon rainforest is not just a resource for survival but a deeply intertwined part of their cultural and spiritual identities. The loss of biodiversity and overall ecosystem degradation threaten socio-ecological systems, which have evolved over centuries and are closely tied to the land and water cycles of the Amazon (Brondízio et al. 2021). As animals and crops disappear and communities are forced to migrate, these rich cultural traditions are at risk (Brondízio et al. 2021; Oestreicher et al. 2017). Furthermore, the inability to access and manage natural resources as they traditionally have—whether due to environmental changes, restricted access, or resource depletion—has significantly weakened the connection between Indigenous peoples and their ancestral lands. Despite the severity of the situation (Figure 2), there is a shocking absence of official data on how these worsening droughts are impacting biodiversity and ecosystem services in the Amazon (Brondízio et al. 2021). Amazonian communities have long been marginalized, and the lack of research makes it difficult for policymakers to develop effective responses to drought problems. Without comprehensive data, the long-term implications of these droughts remain speculative. Expand protected areas Establish and enforce new protected zones focused on freshwater biodiversity, particularly in vulnerable floodplain regions (Correa et al. 2022). Prioritize areas critical for the reproduction and survival of migratory fish and aquatic species (Householder et al. 2024). Implement environmental flows Regulate dam operations to mimic natural flood pulses, ensuring the maintenance of ecological processes that depend on water level fluctuations (Correa et al. 2022). Enhance monitoring infrastructure Expand the network of river gauges across the Amazon basin to provide high-resolution water level data (Householder et al. 2024). Use satellite-based remote sensing technologies to monitor changes in water availability and habitat conditions continuously (Correa et al. 2022). Develop early warning systems Create real-time drought forecasting tools using remote sensing and hydrological models (Householder et al. 2024). Disseminate these forecasts widely to empower communities and policymakers to take timely action (Correa et al. 2022). Incorporate traditional ecological knowledge (TEK) Work closely with Indigenous, quilombola, and riverine communities to integrate their observations and practices into monitoring and management plans (Brondízio et al. 2021). Facilitate community-led resource management to enhance sustainability (Forsberg 2018). Strengthen cross-border cooperation Promote international agreements among Amazonian nations to standardize monitoring protocols and conservation strategies (Householder et al. 2024). Establish rapid response measures for transboundary drought and biodiversity crises (Correa et al. 2022). Address climate change and deforestation Implement policies to reduce greenhouse gas emissions and curb deforestation across the Amazon basin (Lovejoy and Nobre 2018). Support reforestation initiatives and sustainable land-use practices (Lapola et al. 2018). Invest in community resilience Provide resources and training to Amazonian communities to adapt to changing climatic conditions (Brondízio et al. 2021). Support alternative livelihoods and diversify income sources to reduce reliance on increasingly vulnerable ecosystems (Kelly 2024). Thus, by implementing these measures, we can begin to mitigate the impacts of droughts on biodiversity and ecosystem services in the Amazon. Strengthening the integration of science, policy and traditional knowledge will be key to ensuring the sustainability of this globally critical ecosystem. The 2024 drought in the Amazon River basin represents a critical moment for the region's (and global) biodiversity and ecosystem services. The compounded effects of climate change, deforestation and unsustainable land-use practices have pushed the ecosystem to its limits and a possible tipping point, threatening the survival of many species and heavily affecting Amazonian communities. Without urgent actions (see above some examples) to address the root causes of these environmental problems, part of Amazon's rich biodiversity and livelihoods could be irreversibly lost. Efforts to mitigate the effects of climate change, protect the remaining forests, restore degraded habitats, and promote sustainable land use are essential to preserve the ecological integrity of the Amazon as a whole. Addressing the root causes of the drought—climate change, deforestation and fires, is essential to preserving the Amazon for future generations. The time to act is now before the escalating droughts push the Amazon's biodiversity and human populations beyond the brink of survival. We would like to express our gratitude to Thiago B. A. Couto for his insightful feedback and suggestions during the preparation of this manuscript, which greatly contributed to enhancing its scientific quality. The authors have nothing to report. The authors declare no conflicts of interest. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.