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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 is a dominant driver of ET seasonality in most environments, flooding also contributes strongly to ET in tropical and equatorial wetlands, especially in meeting the evaporative demand. Moreover, significant water losses through wetlands and ET differences between wetlands and uplands occur in temperate, more water-limited environments and in highly flooded areas such as the Pantanal, where slow river flood propagation drives the ET dynamics. Finally, floodplain forests produce the greatest ET in all environments except the Amazon River floodplains, where upland forests sustain high rates year round. Our findings highlight the unique hydrological functioning and ecosystem services provided by wetlands on a continental scale. Wetlands can affect regional climate by altering surface-atmosphere interactions. This paper investigates drivers and patterns of evapotranspiration in South American wetlands, from the Amazon floodplains to the large Pantanal system. [ABSTRACT FROM AUTHOR]

This study presents an alternative model for hydrological tracking of surface waters designed to investigate multiyear 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 ) considering the following: (i) the surface water travel times, (ii) the role of large floodable areas (17% of the basin), and (iii) the relations between water composition and lithological sources. Through numerical experiments, we investigated the spatial distribution of in‐stream surface water travel time for the Amazon River Basin (relative to the outlet) and the role of floodplains in seasonal water storage. We estimate that surface water travel time is likely to be less than 90 days (median of 45 days), although about 20% of the flowing water passes through large floodplains. Our modeling exercises indicate that whole‐basin monthly water net balance between river and floodplain can reach up to magnitudes of 105 m3 /s; the water exchanged with floodplains during the annual floods can represent a large portion (up to 40%) of the basin discharge during low waters season. Finally, we took advantage of the tracking approach to study the hydrograph composition based on parent river lithology quantifying the role of major tributaries. Parallel to the development of global hydrology databases, new modeling approaches are also required to push advances in the discussion of renewal and travel times of surface waters in large river basins. [ABSTRACT FROM AUTHOR]

Understanding hydrological processes occurring within a basin by looking at its outlet hydrograph can improve and foster comprehension of ungauged regions. In this context, we present an extensive examination of the roles that floodplains play on driving hydrograph shapes. Observations of many river hydrographs with large floodplain influence are carried out and indicate that a negative skewness of the hydrographs is present among many of them. Through a series of numerical experiments and analytical reasoning, we show how the relationship between flood wave celerity and discharge in such systems is responsible for determining the hydrograph shapes. The more water inundates the floodplains upstream of the observed point, the more negatively skewed is the observed hydrograph. A case study is performed in the Amazon River Basin, where major rivers with large floodplain attenuation (e.g., Purus, Madeira, and Juruá) are identified with higher negative skewness in the respective hydrographs. Finally, different wetland types could be distinguished by using this feature, e.g., wetlands maintained by endogenous processes, from wetlands governed by overbank flow (along river floodplains). A metric of hydrograph skewness was developed to quantify this effect, based on the time derivative of discharge. Together with the skewness concept, it may be used in other studies concerning the relevance of floodplain attenuation in large, ungauged rivers, where remote sensing data (e.g., satellite altimetry) can be very useful. [ABSTRACT FROM AUTHOR]

In this paper, a hydrologic/hydrodynamic modeling of the Amazon River basin is presented using the MGB-IPH model with a validation using remotely sensed observations. Moreover, the sources of model errors by means of the validation and sensitivity tests are investigated, and the physical functioning of the Amazon basin is also explored. The MGB-IPH is a physically based model resolving all land hydrological processes and here using a full 1-D river hydrodynamic module with a simple floodplain storage model. River-floodplain geometry parameters were extracted from the SRTM digital elevation model, and the model was forced using satellite-derived rainfall from TRMM3B42. Model results agree with observed in situ daily river discharges and water levels and with three complementary satellite-based products: (1) water levels derived from ENVISAT altimetry data; (2) a global data set of monthly inundation extent; and (3) monthly terrestrial water storage (TWS) anomalies derived from the Gravity Recovery and Climate Experimental mission. However, the model is sensitive to precipitation forcing and river-floodplain parameters. Most of the errors occur in westerly regions, possibly due to the poor quality of TRMM 3B42 rainfall data set in these mountainous and/or poorly monitored areas. In addition, uncertainty in river-floodplain geometry causes errors in simulated water levels and inundation extent, suggesting the need for improvement of parameter estimation methods. Finally, analyses of Amazon hydrological processes demonstrate that surface waters govern most of the Amazon TWS changes (56%), followed by soil water (27%) and ground water (8%). Moreover, floodplains play a major role in stream flow routing, although backwater effects are also important to delay and attenuate flood waves. [ABSTRACT FROM AUTHOR]

Summary: In this paper, we present a large-scale hydrologic model with a full one-dimensional hydrodynamic module to calculate flow propagation on a complex river network. The model uses the full Saint–Venant equations and a simple floodplain storage model, and therefore is capable of simulating a wide range of fluvial processes such as flood wave delay and attenuation, backwater effects, flood inundation and its effects on flood waves. We present the model basic equations and GIS algorithms to extract model parameters from relatively limited data, which is globally available, such as the SRTM DEM. GIS based algorithms include the estimation of river width and depth using geomorphological relations, river cross section bottom level and floodplain geometry extracted from DEM, etc. We also show a case study on one of the major tributaries of the Amazon, the Purus River basin. A model validation using discharge and water level data shows that the model is capable of reproducing the main hydrological features of the Purus River basin. Also, realistic floodplain inundation maps were derived from the results of the model. Our main conclusion is that it is possible to employ full hydrodynamic models within large-scale hydrological models even using limited data for river geometry and floodplain characterization. [ABSTRACT FROM AUTHOR]

Regional to global river hydrodynamic models are now a reality, and have largely improved in recent years due to increasing computation power and new modeling and remote sensing techniques. Despite all recent advances, it is still necessary to understand to which extent these models can provide locally relevant estimates of variables as discharge, water surface elevation and flood inundation, and how current and future remote sensing data should be used to improve them. We compare here three versions of a river hydrodynamic model (MGB) at local, regional and continental scales. It was applied to the Itajaí-Açu basin in Brazil (15,000 km²) using river spatial discretization, river bathymetry and floodplain DEM representative of local, regional and continental scales. Results are compared to a detailed HEC-RAS model applied at basin scale (>600 cross sections over ~850 km) as a benchmark reference. To evaluate model accuracy, discharge, water levels and flood extent metrics were classified into locally relevance categories based on the accuracy requirement for flood related studies, typical reach scale models' errors, and observation uncertainties. The hydrodynamic model at all scales provided locally relevant discharge estimates, while regional and local versions yielded satisfactory water level anomalies. Less accurate estimates of water level and flood extent indicated the general difficulty on predicting these variables by current large-scale hydrodynamic models. Smaller river reaches (i.e., 1 km river reaches) improved discharge, water level and flood extent estimates. A locally derived DEM did not lead to significant improvements in relation to a global DEM. The cross-scale comparisons also indicate the potential of improving river bathymetry, by means of in situ surveys or remotely sensed river widths and altimetry. In the context of remote sensing, studies like these provide interesting insights on how using future remote sensing data to improve large-scale hydrodynamic models. [ABSTRACT FROM AUTHOR]

Large-scale hydrological models are useful tools for water resources studies, however, river network flow routing is generally represented using simplified methods, which may lead to simulation errors in flat regions. We present recent improvements to the large-scale hydrological model MGB-IPH to improve its capability of simulating large river basins with extensive floodplains. We also describe the coupling of MGB-IPH to an open source GIS and a large set of developed pre-processing tools with a user-friendly interface for remote sensing data preparation and output visualization. The new features implemented are demonstrated applying the model to the whole Araguaia river basin (380,000 km 2 ). Results are compared to the previous MGB-IPH routing method, observed flow and water level data and remote sensing imagery, showing improvement in the representation of floodplain inundation dynamics. The test case also shows that the proposed model software framework amplifies possibilities of large-scale simulation of ungauged basins. [ABSTRACT FROM AUTHOR]