Ayan Santos Fleischmann is a hydrologist with a particular interest in wetlands and large-scale basins, mainly in South America and Africa, and in the context of human impacts on water resources. His main study approaches involve remote sensing techniques and hydrologic-hydrodynamic modeling, as well as interdisciplinary collaborations with other disciplines such as ecology and social sciences. Currently, he is a researcher at the Mamirauá Institute for Sustainable Development (Tefé, Amazonas, Brazil), where he leads the Research Group in Geospatial Analysis of the Amazonian Environment and Territory. He also leads the Conexões Amazônicas initiative for science communication about the Amazon Basin. Ayan holds a PhD degree from UFRGS, with a collaborative period at Université Toulouse III – Paul Sabatier (France). His Ph. D. thesis focused on the hydrology of the South American wetlands. Ayan holds an Environmental Engineering degree from the Universidade Federal do Rio Grande do Sul (UFRGS), with a research stay at the University of East Anglia in the United Kingdom. In this interview, we talked to him about his career path, the work he has been developing in Brazil with wetlands and floods, and his work in the Amazon River basin.

Could you describe your professional and/or personal experience relating to water? Where does your interest in water come from? You undertook your first degree in environmental engineering, which is a vast field. What influenced your decision to focus your work in the water sector, more precisely, in hydrology?

I have been fascinated by water ever since I was a kid. Before entering University, I considered a course in informatics. However, the positive influence of some relatives and friends who were very acquainted with environmental protection made me change my plans. At that time, I had a dream of cleaning up the polluted Lake Guaíba in my hometown (Porto Alegre), and this motivated me to pursue an undergraduate course related to water science. At the Universidade Federal do Rio Grande do Sul (UFRGS), the course in environmental engineering was associated with the Hydraulic Research Institute (IPH), a major institute for water research in Brazil. This set my path towards water resources research. After some time working at IPH’s sanitation lab, I met my Ph.D. supervisor, Walter Collischonn, who leads a great research group in Large Scale Hydrology (https://ufrgs.br/hge), and who sparked my passion for hydrology. Hydrology turned out to be my main subject of study. Later, working with my co-advisor Rodrigo Paiva, I finally found my area of great interest in science – the Amazon hydrology and wetland hydrology in general. Tight collaborations with French researchers, including my Ph.D. co-advisor Fabrice Papa, have further introduced me to the world of remote sensing science. In recent years, I’ve had the pleasure of visiting many wetlands in South America, which fascinate me for their remoteness, unique landscapes, and ecosystems, as well as incredible human communities that have adapted to their challenging environment. Today, I feel very motivated to advance this research agenda and to better understand the dynamic nature of the Mamirauá Reserve and the upper Amazon, where I have been living since the end of 2021.

You have been using innovative technologies to merge new satellite data with hydrological modeling to understand how wetland hydrological processes and floods vary across multiple spatial and temporal scales, and how they respond to environmental changes such as climate change and dam building. What are the main applications of those technologies to wetlands monitoring and conservation?

As a hydrologist, I think of floods from two different perspectives. Firstly, as a natural phenomenon associated with the accumulation of surface water along floodplains of rivers and other types of wetlands. Local ecosystems and human communities need to adapt to the challenges posed by such a dynamic landscape. They also change the environment by means of landscape alteration (e.g., levee building), and thus there is an interesting two-way interaction between ecosystems and humans, from one side, and the hydrological system, from the other. Secondly, floods are also associated with risk management (i.e., floods as a natural hazard), especially along floodplains where humans live. Thus, we need to develop innovative technologies that address both perspectives that allow us to understand, monitor, and predict the spatio-temporal dynamics of multiple hydrological variables. These variables include river and wetland water levels, surface water extent and storage, precipitation, evapotranspiration, and soil moisture. We are now living in the satellite era, so there are new solutions for estimating all these variables from space, with important limitations that need to be understood. This is even more important in the context of current environmental changes, which threaten the provision of ecosystem services by wetlands and enhance flood risks. Hydrology is the basic discipline for understanding the dynamics of a given wetland ecosystem, and thus, advancing it with spatial datasets greatly aids in understanding other aspects such as wetland methane emissions, provision of ecosystem services, and ecosystem dynamics.

You have recently published a complete review about the Amazon hydrology from space. Which role does space-based technology and data play in better understanding the hydrological processes of the largest river basin in the world? What are the gaps that still need to be closed?

The size of the Amazon basin, together with the remoteness of many of its areas, and the transboundary aspect of its multiple tributaries, make it extremely challenging to monitor the hydrology of this basin in the field. Space-based technology plays a major role in improving our understanding of the past and current state of the Amazon hydrological cycle. Given the above-mentioned characteristics and its global relevance for biodiversity, biogeochemistry, and human welfare, the Amazon has been a laboratory for the development of remote sensing techniques to measure multiple aspects of the water cycle. In our recent review published in the AGU’s Reviews of Geophysics, we brought together many experts from different fields of hydrology (i.e., precipitation, surface water, evapotranspiration, etc.) to discuss how satellite data has improved our understanding of the basin’s water resources and fostered the development of remote sensing science itself. Major scientific achievements include groundbreaking monitoring of surface water extent and habitats with L-band synthetic aperture radar data (SAR), identifying rainfall hotspots with satellite-based products such as the IMERG Grand Average Climatology data, understanding the heterogeneity of precipitation and evapotranspiration across the region, and monitoring river water levels with satellite altimetry. However, many gaps remain that are likely to be filled soon with the aid of space technology. For instance, understanding hydrological extremes such as spatial distribution of floods and droughts, as well as surface dynamics over wetlands (to date, most water level datasets were developed for rivers and not wetlands), and soil moisture dynamics, since it is very challenging for current satellite missions to monitor soil moisture under dense forest vegetation.

You published a review on how to use remote sensing data and flood models to foster flood management in Brazil. How frequently and intensely are flood events expected to occur in Brazil in the coming years? To what extent can space-based technologies and data contribute to avoiding or minimizing the effects of those extreme events in Brazil and how are they already used to that end?

Brazil is a continent-scale country with a wide variation in flood trends across it. Projections of climate change are very dependent on the region of the country that is being assessed. Recent studies have shown that the magnitude and frequency of floods are increasing over Southern Brazil, for example. A similar trend has been observed in Central Amazon. Last year, Manaus, the capital of the Amazonas state, experienced the largest flood in over 119 years of record. While not all regions in Brazil are facing increased floods, what is certain is that an increasing number of people are living near rivers and along floodplains where floods will continue to occur, and thus the overall risk of flooding is increasing. To address this risk, space technologies provide unique data to help with all stages of disaster risk reduction, such as prevention, mitigation, preparedness, response, and recovery from flood events. Space technologies assist stakeholders in understanding the dynamics of flood hazards by mapping flooded areas of past events. Real-time monitoring of floods and river stages based on satellite data is also a reality, with many examples from global (e.g., the Global Flood Partnership) to regional scales (e.g., real-time monitoring of South American river discharges based on the combination of hydrological modeling and satellite and in situ data - https://sardim.herokuapp.com/). The Brazilian National Water Agency (ANA) has also developed its own map of open water areas based on satellite data (https://metadados.snirh.gov.br/geonetwork/srv/api/records/7d054e5a-8cc9…). In addition to flood mapping, space-based technologies are also critical for monitoring the dynamics of affected assets and human populations in the context of socio-hydrology (e.g., are people living closer to rivers and why?), and also different components of the water cycle (such as soil moisture and precipitation) that need to be well monitored if we aim to reduce flood risk. Satellite-based precipitation datasets, for instance, are now widely used by water practitioners in Brazil, in combination with in-situ data.

You have led a team of over 30 experts on Amazon inundation mapping to answer the question: “How much inundation occurs in the Amazon?”. Could you share the main findings of this study?

This study was motivated by the understanding that there are many research groups developing local to basin-scale inundation products for the Amazon, while very few intercomparisons among the developed datasets have been performed. The Amazon wetlands are of global importance, both for biogeochemical cycles and for ecosystem and human support and require a thorough understanding of their flooding dynamics. We, therefore, conducted intensive data collection and curation, totaling 29 inundation datasets and a team of over 30 researchers from around the globe. Our study, which is currently under peer review, shows that 26% of the lowland Amazon basin is estimated as floodable by at least one dataset, while the higher-quality SAR-based products suggest a maximum inundated area of 600,000 ± 82,000 km², which is a much lower value. The minimum inundation extent shows greater disagreements among products when compared to the maximum extent. We have also verified that some wetlands in the basin, especially the interfluvial ones, which are transitional areas less connected to the main rivers and subject to flooding by local runoff (e.g., the Llanos de Moxos region), will require increased scientific effort in the coming years, given the large differences between current inundation datasets to map their dynamics. Overall, we have a good clue of how much inundation occurs in the Amazon, but we are still far from a definitive answer. We are even further away from correctly mapping the temporal dynamics (e.g., flood frequency) of wetland hydrology at high spatial resolutions.

Space-based technology and data are very important tools for your daily work as a researcher and hydrologist. Is it the same for other water professionals or is there a barrier to using space technology? If so, what do you believe can be done to ease the use of those technologies for researchers or practitioners with no experience in that field? What can you recommend that helped you?

I think space-based technology is increasingly used by water professionals worldwide. However, in countries like Brazil and others in South America, there is still a gap between water scientists and practitioners. For some practitioners, the use of spaceborne measurements of river water levels, for instance, is something still associated with “sci-fi movies”, rather than real water management. I believe this has been changing with the increasing accessibility of space-based technology, e.g., through multiple online platforms that allow real-time monitoring of variables such as water levels, flooding, and precipitation and that are freely available to any end-user.  I had very good training in remote sensing during my degree at UFRGS, and courses like the ones I took (e.g., “Remote sensing of the hydrological cycle”, taught by Prof. Rodrigo Paiva and Prof. Anderson Ruhoff) could certainly help other water professionals. I strongly recommend more initiatives of training and capacity building for water professionals in Latin America, for example through summer schools and online free courses in local languages (e.g., Portuguese). In addition, there are open online materials and codes available for processing remote sensing datasets. The major role that satellite data can play in monitoring water resources in countries like Brazil should be made very clear to water professionals, who need to be trained to understand and process space-based data.  The perspective of cloud computing systems such as Google Earth Engine also opens great opportunities for water management of large aquatic systems. I have seen many professionals learning how to use them. Finding good code (with good comments) to acquire and process the data you want can be a great starting point.

With a background in hydrology and hydrologic-hydrodynamic modeling, where do you see the biggest but unexploited potential of space technologies in those sectors?

There are many opportunities and potential to advance hydrologic-hydrodynamic modeling, and thus the monitoring and understanding of the water cycle in general, by merging satellite data with models. This requires the development of new assimilation methodologies, by which hydrological observations are assimilated into models, as well as new and computationally feasible ways to calibrate models with spaceborne observations. It is clear to me that both models and remote sensing data have their own uncertainties so that optimal estimates of the water cycle components would be achieved by merging them. To do so, we need to better understand and characterize space-based estimates with ground truth. This requires extensive fieldwork as well as extensive funding and trained people. Unmanned aerial vehicle (UAV) surveys can play a major role in that, for instance by monitoring flooded areas across large floodplain systems, and by cross-validating spaceborne measurements. Future hydrology-oriented missions monitoring the extent and levels of surface water with an unprecedented spatial and temporal resolution, especially SWOT (with its launch scheduled for late 2022) and the NASA-ISRO SAR Mission (NISAR), will be a milestone for improving hydrological models.

If you had three free wishes to be fulfilled by a Space Agency, what would they be?

It is a great pleasure to see the number of hydrology-oriented missions that are launched/planned by multiple space agencies. However, few of them are designed to monitor tropical environments (e.g. densely forested landscapes), and even less to monitor wetlands. For instance, with current satellite data the hydrology of Amazonian floodplains, which have dense tree cover, is very challenging to monitor – and yet these floodplains play a key role in global biochemistry and biodiversity maintenance. It would be great to see a mission designed to monitor surface water (levels, extent, storage) across tropical wetlands. I also think that initiatives funded by space agencies to train South American water researchers and practitioners to work with satellite data would be very welcome – with, for instance, case studies in the context of the continent and teaching material prepared in local languages (Portuguese and Spanish). I also think that there are South American experts who could be motivated to engage in such efforts. Finally, Brazil is home to some of the largest rivers on Earth, and some major river systems are under increasing human pressure, such as the Paraná basin. I would be very happy to see the Brazilian government developing a national space research agenda that improves the monitoring of its water resources.

What do you need to innovate?

Living close to the Amazon floodplain, in a city far from urban areas and being connected to them only by air or water, is a great inspiration for my work. Getting in touch with the incredible people who live in riparian communities, observing the local ecosystems, is all very inspiring. However, doing science here also means that we need to innovate in many ways to deal with day-to-day challenges. es. Firstly, we can only manage what we measure, and here comes spaceborne monitoring, especially for large and remote areas like the Amazon floodplains. However, implementing state-of-the-art in situ monitoring of the Amazon wetland hydrology is still critical, for instance, to have ground truth to validate satellite data, for variables such as water levels and flows across rivers and floodplains. For that, funding and trained people are increasingly needed and, in many cases, hard to find. Today, many cutting-edge studies about the Amazon hydrology have been conducted by researchers from outside of Amazon, and often even from out of South America. We need to invest in science locally and regionally if we want to promote the sustainable development of the region. There is also a need to attract young Brazilian geoscience researchers who are interested in the Amazon hydrology to work here so that they get to know their object of study better and engage directly in local and regional development. It is usually difficult to attract them due to the scarcity of research grants and the challenges of living in a city far from the large urban centers.

You coordinate a collaborative network called Conexões Amazônicas for science communication with both the academic and non-academic communities as well as data sharing on the Amazonia. How does such an initiative contribute to the protection of the Amazon rainforest in the face of climate change and increased anthropogenic pressure?

Such interdisciplinary efforts are quite rare in science, and I strongly encourage scientists from other regions of the globe to develop similar initiatives – for instance in the Congo River basin, a tropical region with many similarities to the Amazon, and where many studies have been carried out recently. We have received very positive feedback from our readers and colleagues and hope to expand our network in the coming years. While it has been a great challenge for scientists to write texts in everyday language, it has also been a privilege to participate in this initiative. We need non-academic groups to recognize the importance of science in sustaining a good, healthy, and sustainable future for us all. Such initiatives naturally engage more people to become scientists, and we scientists also learn a lot when communicating with non-academic people.

Despite the abundance of natural resources, including freshwater, the Amazon region presents low socio-economic indicators when compared to the other regions of Brazil. In your opinion, what are the main challenges for the sustainable development of the Amazon region for the next years? What stakeholder groups in your opinion need to sit together to address and develop solutions for the Amazon region?   

The Amazon region has the great potential to become a source of development in South America and the globe. The immense potential of its standing forest and aquatic systems, with all the unknown biodiversity and major ecosystem services they provide, need to be better understood and managed. Investment in science is paramount to this, and societies in all the Amazon countries (not only those along the biome, but also people from distant urban areas such as in Southern Brazil) need to be informed about its importance and engaged in this endeavor. True interdisciplinary approaches in science, bringing together experts from many research fields (ecology, hydrology, sociology, etc.), are needed to tackle these challenges – one example is provided by a recent paper in Science (https://www.science.org/doi/abs/10.1126/science.abj4017) that we have published, where several international researchers, led by Prof. Alex Flecker and Prof. Carla Gomes from Cornell University, jointly developed a new computational tool that optimizes the allocation of future Amazon dams in order to reduce impacts on multiple environments and ecosystem services. The Amazonian societies have the challenge of adapting to an increasingly unpredictable environment, with recent extreme floods in central Amazon and droughts in the southern region, as well as ongoing human pressure such as deforestation. These factors threaten many traditional communities to become climate refugees. They have a great opportunity to develop adaptation strategies that consider the sustainable use of the Amazon resources, and for that, local, regional and national governments, as well as international stakeholders, need to assist them in a much better way than what has been done so far. We need better public policies geared towards sustainable development. Furthermore, more investment is needed. One crucial example is the need for better Internet connection in remote areas of the Amazon to foster their development and connect the multiple communities living there. Water and food security is also a great challenge for Amazonian rural communities: they often have access to water in quantity but not quality, and food availability, as well as their nutrition balance, are threatened by a changing climate. Nevertheless, I want to finish this interview with a positive perspective: there are many interesting ongoing initiatives in Amazon, and I am very optimistic about the young people that are committed to sustainably developing the region. This is one of the reasons why I moved to Tefé, in the heart of the Amazon.

What is your favorite aggregate state of water and why?

Liquid. Its dynamics and plasticity have always attracted my attention and motivated my research. In special, the mysterious flowing waters of a deep river, with all its hidden biodiversity.