Amazon hydrology from space: scientific advances and future challenges

Abstract

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 techniques using satellite RS in the Amazon. We show how RS played a major role in supporting new research and key findings regarding the Amazon water cycle, and how the region became a laboratory for groundbreaking investigations of new satellite retrievals and analyses. At the basin-scale, the understanding of several hydrological processes was only possible with the advent of RS observations, such as the characterization of "rainfall hotspots" in the Andes-Amazon transition, evapotranspiration rates, and variations of surface waters and groundwater storage. These results strongly contribute to the recent advances of hydrological models and to our new understanding of the Amazon water budget and aquatic environments. In the context of upcoming hydrology-oriented satellite missions, which will offer the opportunity for new synergies and new observations with finer space-time resolution, this review aims to guide future research agenda toward integrated monitoring and understanding of the Amazon water from space. Integrated multidisciplinary studies, fostered by international collaborations, set up future directions to tackle the great challenges the Amazon is currently facing, from climate change to increased anthropogenic pressure. Plain Language SummaryThe Amazon basin is the largest river basin in the world, characterized by complex hydrological processes that connect high rates of precipitation, extensive floodplains, dense tropical forests, complex topography, and large variations in freshwater storage and discharge. It plays a key role in the water, energy, and carbon cycles and interacts with the global climate system. Earth observations have played a major role in supporting research in Amazon hydrology, and the characterization of several hydrological processes was only possible with the help of remote sensing data. The basin is now facing great risk under current climate change and increased anthropogenic pressure and the resulting environmental alterations require a better understanding of the overall basin's water cycle across scales. We review the strengths and limitations of observations from satellites in the context of the current and upcoming hydrology-oriented satellite missions, and we make recommendations for improving satellite observations of the Amazon basin water cycle, along with an interdisciplinary and stepwise approach to guide research for the next decades.

Spatiotemporal Variations of Evapotranspiration in Amazonia Using the Wavelet Phase Difference Analysis

“…The strong resonance at multi‐year (2–4 years) periodicities between ET and P , between ET and TWSA , and between ET and LAI are evident (Figure S2a, S2b, and S2d in Supporting Information ), while the strong resonances at the 1‐year periodicity between P / TWSA / DSR / LAI and ET are significant and discontinuous. These possibly relate to long‐term climatic drivers (e.g., El Niño with ∼3–∼7 years periodicity) or the tropical Atlantic and Pacific Sea surface anomalies (∼2–∼6 years periodicity) (Fassoni‐Andrade et al., 2021). Their discontinuous resonances at intra‐annual periods correspond to the significant high‐power regions at 2–6 months period (Figure S1 in Supporting Information ).…”

A regional view of the linkages between hydro‐climatic changes and deforestation in the Southern Amazon

“…This data set is based on merged precipitation models by interpolation of rainfall in situ data. The version 2 (CHIRPS v2) has a spatial resolution of 5 km and showed an adequate performance for the Amazon Basin when evaluated against ground‐based rainfall stations and in situ discharge observations to represent interannual and multi‐decadal variability and interannual trends (Wongchuig et al ., 2017; Haghtalab et al ., 2020; Fassoni‐Andrade et al ., 2021).…”

Biotic Indicators for Ecological State Change in Amazonian Floodplains

“…Hydrological (vertical flow) and hydraulic (lateral flow) modeling of Amazonian floodplains advanced tremendously over the last three decades thanks to improved remote sensing technology and multi-satellite analytical approaches (reviewed by Fassoni-Andrade et al. 2021 ). Yet modeling the flood pulse within dense floodplain forests and floating macrophytes is still hindered by the lack of high-resolution digital elevation models that capture fine-scale changes in topography (Fassoni-Andrade et al.…”

“…Yet modeling the flood pulse within dense floodplain forests and floating macrophytes is still hindered by the lack of high-resolution digital elevation models that capture fine-scale changes in topography (Fassoni-Andrade et al. 2021 , Melack and Coe 2021 ). Although the daily discharge of many large rivers is currently monitored by water-level gauges, mainly in the Brazilian Amazon, these gauges are located in river channels and do not capture fine-scale hydrological variability within floodplains (e.g., overbank flooding versus flooding through channels; Melack and Coe 2021 ).…”