Spatial and temporal complexity of the Amazon flood measured from space

Alsdorf, D. E.; Bates, Paul; Mélack, John M.; Wilson, Matthew; Dunne, Thomas

doi:10.1029/2007gl029447

Cited by 156 publications

(157 citation statements)

References 27 publications

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“…they are either at one point or represent a full channel cross section), meaning that no information on water-surface area or two-dimensional patterns in water-surface slope is provided. However, synthetic aperture radar (SAR) interferometry work by Alsdorf et al (2007a) has shown that water flow is both spatially and temporally complex, requiring twodimensional, multi-temporal measurements to be captured sufficiently. This means that our current, operational remote sensing has limited capability with regard to an important component of the water surface (Alsdorf et al, 2007b).…”

Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 99%

Swath-altimetry measurements of the main stem Amazon River: measurement errors and hydraulic implications

Wilson

Durand

Jung

et al. 2015

Hydrol. Earth Syst. Sci.

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Abstract. The Surface Water and Ocean Topography (SWOT) mission, scheduled for launch in 2020, will provide a step-change improvement in the measurement of terrestrial surface-water storage and dynamics. In particular, it will provide the first, routine two-dimensional measurements of water-surface elevations. In this paper, we aimed to (i) characterise and illustrate in two dimensions the errors which may be found in SWOT swath measurements of terrestrial surface water, (ii) simulate the spatio-temporal sampling scheme of SWOT for the Amazon, and (iii) assess the impact of each of these on estimates of water-surface slope and river discharge which may be obtained from SWOT imagery. We based our analysis on a virtual mission for a ∼ 260 km reach of the central Amazon (Solimões) River, using a hydraulic model to provide water-surface elevations according to SWOT spatio-temporal sampling to which errors were added based on a two-dimensional height error spectrum derived from the SWOT design requirements. We thereby obtained water-surface elevation measurements for the Amazon main stem as may be observed by SWOT. Using these measurements, we derived estimates of river slope and discharge and compared them to those obtained directly from the hydraulic model. We found that cross-channel and along-reach averaging of SWOT measurements using reach lengths greater than 4 km for the Solimões and 7.5 km for Purus reduced the effect of systematic height errors, enabling discharge to be reproduced accurately from the water height, assuming known bathymetry and friction. Using cross-sectional averaging and 20 km reach lengths, resultsshow Nash-Sutcliffe model efficiency values of 0.99 for the Solimões and 0.88 for the Purus, with 2.6 and 19.1 % average overall error in discharge, respectively. We extend the results to other rivers worldwide and infer that SWOT-derived discharge estimates may be more accurate for rivers with larger channel widths (permitting a greater level of cross-sectional averaging and the use of shorter reach lengths) and higher water-surface slopes (reducing the proportional impact of slope errors on discharge calculation).

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Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 99%

Swath-altimetry measurements of the main stem Amazon River: measurement errors and hydraulic implications

Wilson

Durand

Jung

et al. 2015

Hydrol. Earth Syst. Sci.

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“…The importance of these mechanisms, e.g. overtopping of topographical barriers and flow in floodplain channels, on the dynamics of floodplain inundation is crucial to the modelling of those dynamics in rural (Nicholas and Mitchell, 2003;Bates et al, 2006;Alsdorf et al, 2007) and urban areas (Schumann et al, 2011).…”

Section: Surface Water Connectivitymentioning

confidence: 99%

Surface water connectivity dynamics of a large scale extreme flood

Trigg

Michaelides

Neal

et al. 2013

Journal of Hydrology

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During flood inundation, river water passes from the main channel into the floodplain through floodplain channels and diffusive overbank flow. This flood water is then distributed within the floodplain depending upon internal connections, barriers and storage, and finally returns back to the river through drainage connections. This surface water connectivity can be complex and is important to many aspects of floodplain functioning, including ecology, sediment movement and flood risk. However, there is currently no accepted way of quantifying this connectivity objectively. We quantify surface water connectivity geostatistically as an objectively measurable characteristic of an observed flood event using a time series of MODIS (Moderate Resolution Imaging Spectroradiometer) surface water product for an extreme large scale flood event (11,000 km 2 flooded area and 6 month duration) during 2011 in Bangkok, Thailand. We develop and apply a new gap filling method that better preserves the dynamic information of the event than simple aggregation methods. Comparison of MODIS results with the higher resolution Earth Observer 1 shows fundamental differences in the resolved connectivity with scale despite similar flooded area. The effect of the passage of the flood wave is directly observable in the river reach, as out-of-bank flooding progresses and increases connectivity along the river during rising water. Around peak flow, there is an increase in connectivity of the floodplain adjacent to the river as low lying areas fill. A step increase in connectivity is correlated with a major levee breach. During recession there is a rapid reduction in along river connectivity in the first week after the peak. This rapid reduction contrasted with a slow decrease in the floodplain connectivity as flooded depressions gradually drained reducing depth, while flood extent remained static for long periods. The connectivity analysis of the threshold in floodplain draining indicates that although spatial flood extent changes are small at this time, there is a reorganisation of the internal surface water connectivity within the flooded area. Thus through this measure of connectivity, we can see a clear structure to the event progression with new insights into flood dynamics that were not anticipated a priori.

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“…For instance, synthetic aperture radars (SARs) show very large capabilities to measure surface water extent. Studies in the Amazon basin [Smith and Alsdorf, 1998;Hess et al, 2003;Alsdorf et al, 2007b] or in the Congo prove the ability of SAR to delineate accurately the surface water in tropical forest environments with high spatial sampling intervals (∼100 m). However, large data volumes have limited these studies to a few samples of a few basins, preventing systematic, long-term assessments of inundation dynamics.…”

Section: Introductionmentioning

confidence: 99%

Interannual variability of surface water extent at the global scale, 1993–2004

et al. 2010

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[1] Land surface waters play a primary role in the global water cycle and climate. As a consequence, there is a widespread demand for accurate and long-term quantitative observations of their distribution over the whole globe. This study presents the first global data set that quantifies the monthly distribution of surface water extent at ∼25 km sampling intervals over 12 years (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004). These estimates, generated from complementary multiple-satellite observations, including passive (Special Sensor Microwave Imager) and active (ERS scatterometer) microwaves along with visible and near-infrared imagery (advanced very high-resolution radiometer; AVHRR), were first developed over 1993-2000. The ERS encountered technical problems in 2001 and the processing scheme had to be adapted to extend the time series. Here we investigate and discuss the adjustments of the methodology, compare the various options, and show that the data set can be extended with good confidence beyond 2000, using ERS and AVHRR mean monthly climatologies. In addition to a large seasonal and interannual variability, the new results show a slight overall decrease in global inundated area between 1993 and 2004, representing an ∼5.7% reduction of the mean annual maximum in 12 years. The decrease is mainly observed in the tropics during the 1990s. Over inland water bodies and large river basins, we assess the variability of the surface water extent against related variables such as in situ river discharges, altimeter-derived and in situ river/floodplain water level heights, and precipitation estimates. This new 12 year data set of global surface water extent represents an unprecedented source of information for future hydrological or methane modeling.

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Spatial and temporal complexity of the Amazon flood measured from space

Cited by 156 publications

References 27 publications

Swath-altimetry measurements of the main stem Amazon River: measurement errors and hydraulic implications

Swath-altimetry measurements of the main stem Amazon River: measurement errors and hydraulic implications

Surface water connectivity dynamics of a large scale extreme flood

Interannual variability of surface water extent at the global scale, 1993–2004

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