Showing papers by "Walter Collischonn published in 2020"

Trade-Offs Between 1-D and 2-D Regional River Hydrodynamic Models

Abstract: 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.

A Modeling Assessment of Large-Scale Hydrologic Alteration in South American Pantanal Due to Upstream Dam Operation

Abstract: Natural river flow provides the conditions required to sustain freshwater ecosystems, and the greater the departure from the natural regime, the greater the loss of those ecosystems. In South America, new hydropower dams are continuously being constructed and planned in regions within and around the Amazon basin and in the Upper Paraguay river basin, a region notable for the Pantanal, a huge wetland ecosystem that is largely dependent on the flow regime of the Paraguay river and its tributaries. In this context, it is meaningful to examine the hydrological changes caused by the major Manso dam, that is operating since 2001 at the headwaters of one of the major tributaries of the Paraguay river. This was done for the same case study by other authors in previous studies using only gauging stations data. However, those previous assessments were limited due to the confounding effects of climate variability and the necessity of relatively long term observed time series. Here, we applied a modelling approach to evaluate the changes in hydrological regime caused by Manso dam operation. Our modelling approach was based on the combination of the MGB large-scale hydrologic model with the SIRIPLAN large-scale wetland model. The models were applied, using river reaches from 2 to 10 km, in two scenarios during the period from 2003 to 2015. In the first scenario we used naturalized streamflow at the dam site as input to the hydrological model. In the second scenario we used observed reservoir outflow time series as input to the hydrological model. Our results show that Manso dam has a regulation effect that decreases high flows, increases low flows and reduces lateral connectivity. The decrease in high flows is limited to the region upstream of the Pantanal floodplain, while increase in low flows extends into Pantanal. Timing of maximum and minimum flows is less affected, except for the river reach immediately downstream of the dam. Our results improve the assessment of spatial patterns of hydrologic alteration, giving more confidence in the assessment of magnitude and spatial extension of the effects of Manso dam in the Pantanal region.

The great 1983 floods in South American large rivers: a continental hydrological modelling approach

Abstract: This study provides a spatio-temporal analysis of the great floods that occurred in South America in 1983 using hydrometeorological data and outputs from a continental-scale hydrological-hydrodynam...

Advances and challenges in the water sciences in Brazil: a community synthesis of the XXIII Brazilian Water Resources Symposium

Abstract: In this paper we synthesize the special sessions of the XXIII Brazilian Water Resources Symposium 2019 in order to understand the major advances and challenges in the water sciences in Brazil. We analyzed more than 250 papers and presentations of 16 special sessions covering topics of Climate Variability and Change, Disasters, Modeling, Large Scale Hydrology, Remote Sensing, Education, and Water Resources Management. This exercise highlighted the unique diversity of natural and human water features in Brazil, that offers a great opportunity for understanding coupled hydrological and societal systems. Most contributions were related to methods and the quantification of water phenomena, therefore, there is a clear necessity for fostering more research on phenomena comprehension. There is a vast network of co-authorship among institutions but mostly from academia and with some degree of regional fragmentation. The ABRhidro community now has the challenge to enhance its collaboration network, the culture of synthesis analysis, and to build a common agenda for water resources research. It is also time for us to be aligned with the international water science community and to use our experiences to actively contribute to the tackling of global water issues.

Scenarios of climate change effects in water availability within the Patos Lagoon’s basin

Abstract: The decision-making processes involving water resources in Brazil and in neighboring countries have been based solely on analyses of the historical behavior of hydroclimatological variables. However, this may lead to inappropriate strategies in regards to the use of natural resources, since the impact of future climate change may significantly affect the availability of water resources. This study proposes an analysis of the variation in water availability of basins within the Patos Lagoon contribution area, which may be a consequence of climatic changes predicted by CMIP5 (Coupled Model Intercomparison Project Phase 5) models, published in the most recent International Panel on Climate Change (IPCC) report. Two 30-year periods were simulated, from 2006 to 2035 and from 2051 to 2080, through the MGB-IPH hydrological model, considering two extreme greenhouse gas scenarios and twenty climate change models. A tendency of increase of the flows was verified in the simulated basin, since over 60% of the simulations indicated some percentage of average flow increase across all discretized modeling units. The analysis of the simulation results indicated that the data from climatic models HadGEM2-ES and GFDL-CM3 used as input in the hydrological model are the ones that respectively provide upper and lower flow thresholds for the ensembled simulations. A joint evaluation of the results generated by these two models, associated with the scenario of high greenhouse gas emissions, is capable of covering extreme flow scenarios making predictions considering climate change in the Patos Lagoon’s basin. Whereas the results provided by bcc-csm1, BNU-ESM and CNRM-CM5 are similar to the median of the ensemble of simulations generated by all models evaluated in this research. In addition, the northernmost region of the study area was identified as having the highest sensitivity to climate change, as projected by global models of CMIP5 published in AR5.