Ayan Santos Fleischmann

• PhD in Water Resources
• Group leader / Researcher at Instituto de Desenvolvimento Sustentável Mamirauá

In late 2023, the Amazon River Basin experienced its most extreme drought to date, putting its population and ecosystem at risk. Gauges that were still functioning measured the lowest river water levels (RWL) on record. Here, satellite observations, including Surface Water Ocean Topography (SWOT), reveal the spread and timing of extremely low RWL a...

The Congo River Basin (CRB), hosting the second-largest tropical forest on Earth, is of global signi cance for the water and carbon cycles. Its population and ecosystems are also strongly dependent on freshwater availability, which is increasingly threatened by current climate change and deforestation. Persistent drought conditions in CRB have been...

La idea de recopilar los estudios relacionados con el ciclo hidrológico de la cuenca amazónica y con la teledetección surgió en 2020 por un grupo de futuros doctores y profesores del Instituto de Pesquisas Hidráulicas (Instituto de Investigaciones Hidráulicas) (IPH - UFRGS). Cada uno era especialista en un área y no parecía complicado escribir un...

While the 2023 record-breaking drought led to widespread social-ecological impacts across Amazonia, local impacts of such extreme events are rarely described in detail. Here we leverage a large interdisciplinary data collection related to social and ecological impacts in the Central Amazon. Compound hazards (reduced river water levels, lack of rain...

Sedimentary processes cause large changes in riverscapes and alter river banks and margins, leading to major hazards for riverine communities. However, regional mapping of the resulting risk remains scarce, especially in remote Amazon regions. Here, we combine environmental observations with regional socioeconomic information to map erosion and sed...

The climate extreme is imposing several threats to Amazonian ecosystems. In 2023, an extreme drought in the Amazon basin and the impacts were measured in the Tefé and Coari lakes, including unprecedented river dolphin mortality and phytoplankton blooms. This study presents the first recorded bloom of Euglena sanguinea in the Amazon, to our knowledg...

Increasing climatic and human pressures are changing the world's water resources and hydrological processes at unprecedented rates. Understanding these changes requires comprehensive monitoring of water resources. Hydrogeodesy, the science that measures the Earth's solid and aquatic surfaces, gravity field, and their changes over time, delivers a r...

Plain Language Summary Understanding and predicting rainfall is a complex task, especially in areas where the availability of data from surface stations is limited, a common feature in many developing regions with insufficient rain gauge coverage. Recently, new opportunistic methods of rainfall measurement have emerged. Among them, is the use of th...

Las fuertes sequías en la Amazonía han ido aumentando en frecuencia e intensidad, de cuatro en un siglo , a cuatro en menos de 25 años, en sintonía con el aumento de la deforestación y el calentamiento global. La sinergia de sequías, deforestación, incendios y degradación forestal, tiene el potencial de llevar a la Amazonía a un punto de no retorno...

In late 2023, the Amazon River Basin experienced its most extreme drought, putting its population and ecosystem at major risks. Gauges that were still functioning measured the lowest river water levels (RWL) on record. Here, satellite observations, including Surface Water Ocean Topography (SWOT), reveal the spread and timing of extremely low RWL ac...

Satellite remote sensing enhances model predictions by providing insights into terrestrial and hydrological processes. While data assimilation techniques have proven promising, there is a lack of standardized and effective approaches for integrating multiple observations simultaneously. This study presents a novel assimilation framework, the multi‐...

-Strong droughts in the Amazon have been increasing in frequency and intensity, from four in a century to four in less than 25 years, in concert with increasing deforestation and global warming. The synergy of droughts, deforestation, fire, and forest degradation have the potential to drive the Amazon to a tipping point where this globally importan...

In 2023, an unprecedented drought and heatwave severely impacted Amazon waters, leading to high mortality of fishes and river dolphins. Five of 10 lakes monitored showed exceptionally high daytime temperatures (>37°C), with one large lake reaching up to 41°C in the entire ~2-m deep water column, with up to 13°C of diel variation. Modeling show that...

We developed and analyzed the performance of an ensemble forecasting system for the Madeira River basin, the largest sub-basin of the Amazon, with forecasts up to 30 days under different hydrometeorological conditions. We used outputs from the regional Eta model of precipitation and global climatological data as inputs to a large-scale hydrological...

Ground weather observations are scarce in many parts of the globe, hampering effective climate monitoring and disaster management. In the Amazon basin, this occurs due to its remoteness and the challenging measurement of rainfall within the forest. Innovative rainfall estimation methods are thus requested to fill this gap. Here we present an approa...

The catastrophic heatwave and drought that hit the Amazon at the end of last year (see L. Santos de Lima et al. Nature 622, 697; 2023) has led to the unprecedented mortality of hundreds of its river dolphins. A better understanding of how climate change affects biodiversity in tropical water bodies is needed for more effective management of these s...

Monitoring actual evapotranspiration (ET) is critical for the accurate assessment of water availability and water resources management, especially in areas with dry climates and frequent droughts. The Surface Energy Balance Algorithm for Land (SEBAL) has been used over several land and climate conditions, and is able to estimate ET at field scale w...

River damming has brought great benefits to flood mitigation, energy and food production, and will continue to play a significant role in global energy supply, particularly in Asia, Africa, and South America. However, dams have extensively altered global river dynamics, including riverine connectivity, hydrological, thermal, sediment and solute reg...

Reservoir cascades are built on many rivers around the world in order to use water resources for power generation and human supply. In this work, the impact of a reservoir cascade on sediment transport and deposition in time and space was studied. The study area chosen was the Paranapanema River basin, which has 10 reservoirs in the main river. The...

O livro Hidrologia da Amazônia vista do espaço: avanços científicos e desafios futuroso é uma tradução do artigo de revisão não sistemática publicado em 2021 na Review of Geophysics (https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020RG000728). O livro apresenta uma extensa revisão das conquistas de mais de três décadas de avanços científicos...

In the Amazon, aquatic ecosystems provide essential ecosystem services, including transportation, food, and livelihoods for millions of species. Land use changes and management impact these ecosystem services and these impacts are not limited to the specific areas where they occur but propagate downstream along the drainage network. However, assess...

Study region: The Congo River basin (CRB), the world's second-largest river system, is subject to extreme hydrological events that strongly impact its ecosystems and population. Study focus: Here we present an improved 40-year (1981-2020) hydrological reanalysis of daily CRB discharge and analyze the spatiotemporal dynamics of recent major CRB floo...

As air temperatures soar to record highs in parts of the Amazonia, water levels are falling fast (see go.nature. com/3pvdgve). Authorities have announced emergency measures against impending drought, aware that millions have been harmed by extreme droughts in the past. This year, the emergence of El Niño and the unusually high sea surface temperatu...

http://www.jornaldaciencia.org.br/seca-extrema-nos-rios-e-incendios-na-amazonia-um-chamado-a-acao/

Evapotranspiration (ET) is a key process linking surface and atmospheric energy budgets, yet its drivers and patterns across wetlandscapes are poorly understood worldwide. Here we assess the ET dynamics in 12 wetland complexes across South America, revealing major differences under temperate, tropical, and equatorial climates. While net radiation i...

Deforestation and climate change threaten social and ecological well-being in Amazonia. Research co-produced through ethical collaborations across multiple knowledge systems can contribute toward just and sustainable futures for the region. Accelerating deforestation and degradation in Amazonia are undermining the resilience of one of Earth's most...

The spatio-temporal variation of surface water storage (SWS) in the Congo River basin (CRB), the second-largest watershed in the world, remains widely unknown. In this study, satellite-derived observations are combined to estimate SWS dynamics at the CRB and sub-basin scales over 1992–2015. Two methods are employed. The first one combines surface w...

Extreme droughts and floods in the Amazon have great implications for ecosystems and societies. Over the last decade, the region has undergone major extreme events with no equivalent in the previous 100 years. Wetlands have been greatly impacted by these events. This study aims at presenting new indicators for wetlands based on Water Surface Extent...

We provide a new dataset of simulated suspended sediment discharge for South American rivers using daily hydrologic-hydrodynamic modeling. From the previous version (10.17632/k7c5482fsm.1) we improved our results by simulating 234 large reservoirs in South America and also by considering 8 land use and land cover maps. We also extended our simulate...

River sediment fluxes have been impacted in South America (SA), one of the continents with the highest erosion and sediment transport rates globally. However, the magnitude and spatio‐temporal distribution of the main drivers of changes have been poorly identified and explored. Here, we performed simulations using a hydrological‐hydrodynamic‐sedime...

Southwestern Amazonia has low spatial coverage of hydro-meteorological data, making climate and hydrological models essential tools. Thus, it is necessary to evaluate these models to verify their suitability for future climate change assessments. We evaluate the ability of a regional climate model (Eta) forced with three Earth system models and a l...

A Área de Relevante Interesse Ecológico Javari-Buriti é uma Unidade de Conservação federal que esteve perto de completar 40 anos desde a sua criação e ainda ser considerada uma das áreas menos conhecidas da Amazônia brasileira. Em seu Artigo 1º, o Decreto nº 91.886 de 1985, determinou que “sob a denominação de Javari-Buriti, fica declarada Área de...

• A novel methodology was developed for the application of the geeSEBAL model to very large scales, overcoming the issues associated to domain size selection; • Development of a 20-yr (2002-2021) actual evapotranspiration dataset with complete spatial coverage for South America, providing 8-day evapotranspiration data at 500 m, hereon named geeSEBA...

Extensive floodplains throughout the Amazon basin support important ecosystem services and influence global water and carbon cycles. A recent change in the hydroclimatic regime of the region, with increased rainfall in the northern portions of the basin, has produced record-breaking high water levels on the Amazon River mainstem. Yet, the implicati...

Sediment flows dynamics (erosion, transport and deposition) have been disrupted in South America (SA), a continent with the highest erosion and sediment transport rates globally. However, the magnitude and spatial distribution of the main drivers of changes have been poorly identified and explored. Here, we performed simulations using a hydrologica...

Drought events have been reported in all Brazilian regions every year, evolving slowly over time and large areas, and largely impacting agriculture, hydropower production, and water supplies. In the last two decades, major drought events have occurred over the country, such as the 2010 and 2015 events in the Amazon, the 2012 event in the Pampa, and...

The spatio-temporal variation of surface water storage (SWS) in the Congo River basin (CRB), the second largest watershed in the world, remains widely unknown. In this study, satellite-derived observations are combined to estimate SWS dynamics at the CRB and sub-basin scales over 1992–2015. Two methods are employed. The first one combines surface w...

Brazil hosts a large amount of freshwater. Knowing how this stored water is partitioned in space and time between surface and subsurface components is a crucial step towards a more correct depiction of the country’s water cycle, which has major implications for decision making related to water resources management. Here, we extracted monthly water...

Os reservatórios são estruturas feitas pelo homem que tem contribuído para a redução dos sedimentos em diversos trechos de rios e consequentemente para os oceanos. O objetivo deste trabalho foi avaliar a performance de um modelo de sedimentos continental em representar os fluxos de sedimentos em suspensão e de leito, considerando a presença de 234...

The Amazon River basin harbors some of the world's largest wetland complexes, which are of major importance for biodiversity, the water cycle and climate, and human activities. Accurate estimates of inundation extent and its variations across spatial and temporal scales are therefore fundamental to understand and manage the basin's resources. More...

Evapotranspiration (ET) connects the land to the atmosphere, linking water, energy, and carbon cycles. ET is an essential climate variable with a fundamental importance, and accurate assessments of the spatiotemporal trends and variability in ET are needed from regional to continental scales. This study compared eight global actual ET datasets (ETg...

Key challenges to regionalization of methane fluxes in the Amazon basin are the large seasonal variation in inundated areas and habitats, the wide variety of aquatic ecosystems throughout the Amazon basin, and the variability in methane fluxes in time and space. Based on available measurements of methane emission and areal extent, seven types of aq...

Mapping flood risk areas is important for disaster management at the local, regional, and national scales. The aim of this study was to evaluate the ability of large-scale models to obtain flood hazard maps. The models were compared to the estimates developed by the Brazilian Geological Survey (CPRM) for different return periods (RP). The floods we...

The African continent hosts some of the largest freshwater systems worldwide, characterized by a large distribution and variability of surface waters that play a key role in the water, energy and carbon cycles and are of major importance to the global climate and water resources. Freshwater availability in Africa has now become of major concern und...

The Congo River basin (CRB) is the second largest river system in the world, but its hydroclimatic characteristics remain relatively poorly known. Here, we jointly analyse a large record of in situ and satellite-derived observations, including a long-term time series of surface water height (SWH) from radar altimetry (a total of 2311 virtual statio...

This study intends to integrate heterogeneous remote sensing observations and hydrological modeling into a simple framework to monitor hydrological variables in the poorly gauged Congo River Basin (CRB). It focuses on the possibility of retrieving effective channel depths and discharges all over the basin in near real time (NRT). First, this paper...

Proposed hydropower dams at more than 350 sites throughout the Amazon require strategic evaluation of trade-offs between the numerous ecosystem services provided by Earth’s largest and most biodiverse river basin. These services are spatially variable, hence collective impacts of newly built dams depend strongly on their configuration. We use multi...

Cette étude a pour but d'intégrer des observations hétérogènes de télédétection et la modélisation hydrologique dans un cadre simple pour le suivi des variables hydrologiques dans le bassin du fleuve Congo (CRB), qui est peu jaugé. Elle se concentre sur la possibilité d'estimer les profondeurs et les débits effectifs des rivières sur l'ensemble du...

Satellite observations offer invaluable insights into hydrological processes and environmental change in the Amazon. The Amazon Basin is the largest river basin in the world. It covers roughly six million square kilometers, which is about one third of South America. While the sheer scale and difficulty of access makes field observations challengin...

This report summarises the main results, conclusions and recommendations of the “HYDROSPACE-GEOGLOWS 2021” Workshop organised by the European Space Agency (ESA), in collaboration with the French Space Agency (CNES) and the GEO Global Water Sustainability Initiative (GEOGloWS) (Fig. 1). This Workshop is a sequel to the ones held in Toulouse (F) in 2...

Reservatórios tem sido um tema central em diversos assuntos atuais como crise hídrica, geração de energia, retenção de sedimentos, redução da conectividade de rios e impacto nos ecossistemas. O objetivo do presente trabalho foi estimar pela primeira vez a vida útil dos grandes reservatórios da América do Sul, buscando compreender o impacto dos rese...

RESUMO - Eventos extremos de secas possuem comportamentos distintos em cada região do Brasil, associados à sua intensidade e tempo de duração, gerando diversos efeitos ambientais e socioeconômicos. Este estudo avaliou eventos extremos de secas ocorridos em diferentes regiões do Brasil, sendo estas: a Região Norte – Amazônia (seca de 2010), a Região...

As the largest river basin on Earth, the Amazon is of major importance to the world's climate and water resources. Over the past decades, advances in satellite‐based remote sensing (RS) have brought our understanding of its terrestrial water cycle and the associated hydrological processes to a new era. Here, we review major studies and the various...

Numerous hydropower facilities are under construction or planned in tropical and subtropical rivers worldwide. While dams are typically designed considering historic river discharge regimes, climate change is likely to induce large-scale alterations in river hydrology. Here we analyze how future climate change will affect river hydrology, electrici...

Hydrological models are useful tools for water resources studies, yet their calibration is still a challenge, especially if aiming at improved estimates of multiple components of the water cycle. This has led the hydrologic community to look for ways to constrain models with multiple variables. Remote sensing estimates of soil moisture are very pro...

The Congo River Basin (CRB) is the second largest river system in the world, but its hydroclimatic characteristics remain relatively poorly known. Here, we jointly analyze a large record of in situ and satellite-derived observations, including long term time series of Surface Water Height (SWH) from radar altimetry (a total of 2,311 virtual station...

Accurate estimation of evapotranspiration (ET) is essential for several applications in water resources management. ET models using remote sensing data have flourished in recent years allowing spatial and temporal assessments at unprecedented resolutions. This study presents geeSEBAL, a new tool for automated estimation of ET, based on the Surface...

In Brazil, substantial understanding of flooding regimes in large natural wetlands, as in the Amazon and Pantanal regions, has been promoted through remote sensing (RS) and river flood modeling. However, less research attention has been given to the floods with socioeconomic impacts. In the last decades, RS has provided new opportunities for improv...

This study describes the impacts of refinement of hydraulic geometry (HG) relationships in the hydrological MGB model applied to an Amazonian sub-basin (Purus River basin). To this end, HG relationships were developed for the entire basin and for hydrologically homogeneous regions, and their performances were compared with observed data and a globa...

As the largest river basin on Earth, the Amazon is of major importance to the world's climate and water resources. Over the past decades, advances in satellite-based remote sensing (RS) have brought our understanding of its terrestrial water cycle and the associated hydrological processes to a new era. Here, we review major studies and the various...

Evapotranspiration (ET) is a key process linking surface and atmospheric energy budgets, yet its drivers and patterns across wetlandscapes are poorly understood worldwide. Here we assess the ET dynamics in 12 wetlands complexes across South America, revealing major differences under temperate, tropical, and equatorial climates. While net radiation...

The accuracy of hydrological model predictions is limited by uncertainties in model structure and parameterization, and observations used for calibration, validation and model forcing. While calibration is usually performed with discharge estimates, the internal model processes might be misrepresented, and the model might be getting the "right resu...

Estimating discharges is a major challenge in water resources management, and techniques such as Data Assimilation (DA) can be used to improve these estimates. This study assesses the application of the local ensemble Kalman filter (LEnKF) DA scheme within a large scale hydrological-hydrodynamic model to improve discharge estimates. Different scena...

River floodplains and reservoirs interact throughout a basin drainage network, defining a coupled human-water system with multiple feedbacks. Recent modeling developments have aimed to improve the representation of such processes at regional to continental scales. However, most large-scale hydrological models adopt simplified lumped reservoir schem...

The discretization of river networks is a critical step for computing flow routing in hydrological models. However, when it comes to more complex hydrologic-hydrodynamic models, adaptations in the spatial representation of model calculation units are further required to allow cost-effective simulations, especially for large scale applications. The...

Este capítulo presenta una recopilación de las principales transformaciones de gran escala de los hábitats fluviales de la cuenca del Rio Magdalena, que han resultado de los efectos acumulativos y concurrentes de diversas intervenciones antrópicas. Los análisis integran tres factores principales para cuantificar los cambios en los hábitats de agua...

This study presents an alternative model for hydrological tracking of surface waters designed to investigate multi‐year storage and movement of water in large river basins. We coupled this model with a background solution from a large‐scale hydrological‐hydrodynamic model to study the fate of waters in the Amazon River basin (6 million km2) conside...

We introduce a new catchment dataset for large-sample hydrological studies in Brazil. This dataset encompasses daily time series of observed streamflow from 3679 gauges, as well as meteorological forcing (precipitation, evapotranspiration, and temperature) for 897 selected catchments. It also includes 65 attributes covering a range of topographic,...

Recent years have seen the development of 1D and 2D regional scale hydrological-hydrodynamic models, which differ greatly from reach scale applications in terms of subgrid assumptions, parameterization and applied resolution. Although 1D and 2D comparisons have already been performed at reach and local scales, model differences at regional scale ar...

Large storage dams have widely documented impacts on downstream aquatic environments, but hydroelectric dams with little or no capacity for storage of water inflows (i.e., run-of-river) have received less attention. Two of the world’s largest run-of-river hydropower dams (Jirau and Santo Antônio, Brazil) are located on the Madeira River, the larges...

Topography is critical information for water resources management in lakes, and remote sensing provides a unique opportunity to estimate topography in ungauged regions. We introduce here a new method that estimates nearshore topography of water bodies based on a flood frequency map and time series of water levels by assuming the equivalence between...

Animated GIF of daily rainfall in South America during the 1983 year.

Animated GIF of return period of daily discharges in South American rivers during the 1983 year.

Terrain elevation data are essential for land management, navigation, and earth science applications. Digital elevation models (DEMs) can be created for land as well as underwater surfaces, and remote sensing advancements have led to the increase in the availability of a range of DEMs over the land. However, the generation of underwater DEMs usuall...

Abstract. We introduce a new catchment dataset for large-sample hydrological studies in Brazil. This dataset encompasses daily time series of observed streamflow from 3713 gauges, as well as meteorological forcing (precipitation, evapotranspiration and temperature) for 897 selected catchments. It also includes 63 attributes covering a range of topo...

Topography is critical information for water resources management in lakes, and remote sensing provides a unique opportunity to estimate it in ungauged regions. We introduce here a new method which estimates near shore topography of water bodies based on a flood frequency map and time series of water levels by assuming the equivalence between flood...