Global estimates of river dynamics are needed in order to manage water resources, mainly in developing countries where in-situ observation is limited. Remote sensors such as nadir altimeters can complement ground data. Current altimeters miss however a large number of continental surface water bodies. This issue will be largely resolved by the future Surface Water and Ocean Topography (SWOT) mission, thanks to its wide swath altimeter. SWOT will provide almost globally two-dimensional water elevation maps for rivers over 100 m wide and water bodies over 250 m x 250 m. During this research, we investigated the potential of SWOT to correct hydrological models on a global/continental scale, through data assimilation. For this purpose, an Observing System Simulation Experiment (OSSE), also known as "twin experiment", has been implemented. Model forcings and parameters were perturbed to jointly achieve global hydrological models (GHMs) uncertainties, which is the expected scenario in which the SWOT community will mainly evaluate the future SWOT data. SWOT-like observations of water surface elevation (WSE), flooded water extent (FWE), and/or SWOT derived discharge (Q) were used to correct modelled Q, WSE and FWE from a large-scale hydrological and hydrodynamic model (MGB -portuguese acronym of "Modelo de Grandes Bacias"), using a Ensemble Kalman filter (EnKF). The results indicate that SWOT products could largely improve hydrological simulations on a global and continental scale. SWOT-like discharge can reduce ~40% of model errors in daily discharge. Furthermore, when anomalies of the WSE DA approach were implemented, the error reduction was even greater for all state variables compared to the absolute WSE DA, achieving average error reduction values of about ~30% compared to ~24%. Finally, the simultaneous DA of all the SWOT-like variables together reduces errors from ~14% to ~22% compared to the average of assimilating only one variable.
Os cálculos de propagação de ondas de cheias em rios são, normalmente, realizados utilizando soluções numéricas das equações de Saint-Venant. No entanto, em modelos hidrológicos de transformação chuva-vazão que representam além do escoamento nos rios, os demais processos do ciclo hidrológico, como a geração de escoamento superficial, a evapotranspiração, e o balanço de água no solo, é comum a utilização de métodos simplificados para representar a propagação de cheias em rios. Entre as técnicas de propagação mais utilizadas estão os métodos de onda cinemática e o método Muskingum-Cunge. Essas abordagens simplificadas, entretanto, não permitem representar o escoamento em rios de baixa declividade, em rios sujeitos ao efeito de remanso de reservatórios, e em estuários em que o escoamento está sujeito ao efeito da maré, porque desprezam, entre outros, o termo do gradiente de pressão nas equações de Saint-Venant. Uma alternativa, neste caso, é a utilização dos modelos não inerciais, que incluem o termo do gradiente de pressão. Mais recentemente, novos trabalhos propõe a adoção dos modelos inerciais, que incluem, além do termo do gradiente de pressão, o termo de inércia local. Este artigo apresenta alguns testes da aplicabilidade de uma solução numérica por um esquema explícito do modelo inercial unidimensional, visando sua futura integração como módulo de propagação de vazões em modelos hidrológicos chuva-vazão. O modelo inercial também é comparado com outros modelos simplificados e com uma solução hidrodinâmica completa. O conjunto de testes avaliam os modelos em situações de diferentes declividades, efeito de reservatório e remanso e, por fim, efeito de maré. Os resultados mostram que para uma variedade de casos o modelo inercial apresenta resultados próximos aos de um modelo hidrodinâmico completo, e melhores ou equivalentes que dois modelos simplificados também testados (Muskingum-Cunge Linear e Muskingum-Cunge-Todini não linear). Concluise que o modelo inercial, com solução baseada num esquema numérico explícito, é aplicável para a simulação da propagação de vazão em trechos de rios, e promissor para o acoplamento como módulo de propagação em modelos hidrológicos.
Recent years have seen the development of 1‐D and 2‐D regional‐scale hydrological‐hydrodynamic models, which differ greatly from reach‐scale applications in terms of subgrid assumptions, parameterization, and applied resolution. Although 1‐D and 2‐D comparisons have already been performed at reach and local scales, model differences at regional scale are poorly understood. Moreover, there is a need to improve the coupling between hydrological and hydrodynamic models. It is addressed here by applying the MGB model at 1‐D and 2‐D dimensions for the whole ~700,000 km2 Negro basin (Amazon), which presents different wetland types. Long‐term continuous simulations are performed and validated with multisatellite observations of hydraulic variables. Results showed that both approaches are similarly able to estimate discharges and water levels along main rivers, especially considering parameter uncertainties, but differ in terms of flood extent and volume and water levels in complex wetlands. In these latter, the diffuse flow and drainage patterns were more realistically represented by the 2‐D scheme, as well as wetland connectivity across the basin. The 2‐D model led to higher drainage basinwide, while the 1‐D model was more sensitive to hydrodynamic parameters for discharge and flood extent and had a similar sensitivity for water levels. Finally, tests on the coupling between hydrologic and hydrodynamic processes suggested that their representation in an online way is less important for tropical wetlands than model dimensionality, which largely impacts water transfer and repartition.
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