Toward continental hydrologic–hydrodynamic modeling in South America

Abstract

Abstract. Providing reliable estimates of streamflow and hydrological fluxes is a major challenge for water resources management over national and transnational basins in South America. Global hydrological models and land surface models are a possible solution to simulate the terrestrial water cycle at the continental scale, but issues about parameterization and limitations in representing lowland river systems can place constraints on these models to meet local needs. In an attempt to overcome such limitations, we extended a regional, fully coupled hydrologic–hydrodynamic model (MGB; Modelo hidrológico de Grandes Bacias) to the continental domain of South America and assessed its performance using daily river discharge, water levels from independent sources (in situ, satellite altimetry), estimates of terrestrial water storage (TWS) and evapotranspiration (ET) from remote sensing and other available global datasets. In addition, river discharge was compared with outputs from global models acquired through the eartH2Observe project (HTESSEL/CaMa-Flood, LISFLOOD and WaterGAP3), providing the first cross-scale assessment (regional/continental × global models) that makes use of spatially distributed, daily discharge data. A satisfactory representation of discharge and water levels was obtained (Nash–Sutcliffe efficiency, NSE > 0.6 in 55 % of the cases) and the continental model was able to capture patterns of seasonality and magnitude of TWS and ET, especially over the largest basins of South America. After the comparison with global models, we found that it is possible to obtain considerable improvement on daily river discharge, even by using current global forcing data, just by combining parameterization and better routing physics based on regional experience. Issues about the potential sources of errors related to both global- and continental-scale modeling are discussed, as well as future directions for improving large-scale model applications in this continent. We hope that our study provides important insights to reduce the gap between global and regional hydrological modeling communities.

The Effects of Land Use and Climate Change on the Water Yield of a Watershed in Colombia

“…For the level of performance rating of our model, having a longer period for validation would have averaged out this condition of large flows and potentially resulted in better error metrics for the validation phase. The uncertainty of the discharge estimates in our study relates with the modeling effort of Siqueira et al (2018) [64], which, for continental South America, using gauging station data and a "regions of parameter sets" calibration strategy, had satisfactory fits (NSE > 0.6) between modeled and observed values for 55% of the gauging stations evaluated. Some of the lower fits were located in regions strongly influenced by orography.…”

Assimilation of Satellite Altimetry Data for Effective River Bathymetry

“…It is derived from the Saint Venant equations, neglecting only the convective inertia term from the momentum equation: where t indicates time and x is related to longitudinal position; g is acceleration due to gravity; q a is the lateral inflow; A is the cross section area; R represents the hydraulic radius; and W , Y , and Q represent the river width, WSE, and discharge, respectively. Large‐scale models such as CaMa‐Flood, MGB, and LISFLOOD‐FP (Neal et al, ; Pontes et al, ; Siqueira et al, ; Yamazaki et al, ) adopt a similar 1D inertial model for river flow routing.…”

“…Further, its size is compatible with large-scale hydrological and hydraulic model applications. The Madeira River was simulated using a 1D hydrodynamic model based on the inertial model (Bates et al, 2010), which is frequently used for large-scale studies (Neal et al, 2012;Siqueira et al, 2018;Yamazaki et al, 2013). Altimetry data from ICESAT, ENVISAT, and JASON 2 were assimilated to correct the model parameters, bed elevation, and Manning's roughness at each reach.…”

“…Large-scale hydrologic and hydrodynamic models running at regional to global scales are used for several purposes (Bierkens, 2015;Siqueira et al, 2018;Yamazaki et al, 2011;Neal et al, 2012). These purposes include hydrological forecasting (Alfieri et al, 2012;Fan et al, 2014), prediction of climate changes impact on water resources (Sorribas et al, 2016), mapping flood risks (Trigg et al, 2016), and supporting studies on hydrological processes.…”

Lessons learnt from checking the quality of openly accessible river flow data worldwide

“…Lehner and Döll 2004, Portmann et al 2010, Yamazaki et al 2014) has further enhanced opportunities for large-scale and large-sample hydrological studies (e.g. Pechlivanidis and Arheimer 2015, Siqueira et al 2018, Arheimer et al 2019. In hydrology, river flow is one of the most crucial variables for water resources projects, such as energy production, irrigation planning, water quality improvements or waterway transport.…”