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This paper aims to estimate the variation of the combined dependable energy output of the set of major hydropower plants within the Brazilian part of the La Plata Basin due to possible climate changes during the twenty-first century. It uses and compares the predictions of two regional climate models, namely PROMES [Castro, M., Fernández, C., and Gaertner, M.A., 1993. Description of a mesoscale atmospheric numerical model. In: J.I. Díaz and J.L. Lions, eds.Mathematics, climate and environment. Rech. Math. Appl. Ser. Mason, 230–253; Gallardo, A., Galvan, C., and Mermejo, R., 2012.PROMES-MOSLEF: An atmosphere-ocean coupled regional model. Coupling and preliminary results over the Mediterranean basin. 4th HYMEX Workshop 2 2010] and RCA models [Rummukainem, M., 2010. State-of-the-art with regional climate models.WIREs Climate Change, 1, 82–96]. Rainfall and temperature predictions are converted into streamflow at key gauge stations using Variable Infiltration Capacity Model [Liang, X., Lettenmaier, D.P., Wood, E.F., and Burges, E.F., 1994. A simple hydrologically based model of land surface water and energy fluxes for general circulation models.Journal of Geophysical Research, 99, n. D7, 14,451–14,428]. The evaluation of the dependable energy output used the natural energy hydrograph method engineering consultants (Canambra Engineering Consultants, 1969.Power study of South Brazil. 13 v. Appendice XVII Final Report. Rio de Janeiro: Canambra Engineering Consultants), combined with the Monte Carlo simulation of synthetic series of natural energy. The main contribution of this paper is the consolidation of a methodology that provides estimates of the system's dependable energy as a function of the return period for both observed and future predicted streamflows. As a conclusion, a reduction of the dependable energy output of the hydropower plants within the La Plata Basin could be expected during the twenty-first century [ABSTRACT FROM PUBLISHER]

This paper reviews recent progress made in our understanding of the functioning and variability of the South American Monsoon System (SAMS) on time scales varying from synoptic to long-term variability and climate change. The SAMS contains one of the most prominent summertime climate patterns in South America, featuring a strong seasonal variability in a region lying between the Amazon and the La Plata Basin. Much of the recent progress is derived from complementary international programs, such as the Monsoon Experiment South America (MESA), as well as from ongoing international programs such as the Large Scale Biosphere Atmosphere Experiment in the Amazon Basin (LBA) and the La Plata Basin (LPB) Regional Hydroclimate Project, which includes the CLARIS LPB Europe-South America Network for Climate Change Assessment and Impact Studies in La Plata Basin Project. The latter assesses atmosphere-land surface interactions, the role of land use changes and aerosols from biomass burning considered as sources of variability and change in the SAMS functioning, characteristics and behaviour. The SAMS region is particularly susceptible to variations of climate due to the importance of hydroelectricity generation and the agricultural base of local economies. Also addressed in this report are projections of climate change and extremes, which are important for impact and vulnerability assessments. This discussion includes the need to identify and understand important processes that control the monsoonal climate, how these processes may vary and change, and how they may interact with key societal sectors, including water resource management, hydroelectric generation, agriculture, and agribusiness. This paper reports on the major contributions of MESA to the knowledge of characteristics, functioning and variability of the SAMS, and is based on recent studies and publications, and can be considered as an update of a previous review by C. S. Vera et al. (2006a). Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

In a Climate Change context, it is relevant to assess the potential impacts of variations of climate drivers on sediment yield from basins with high soil exportation rates. This paper develops a methodology, based on the erosion potential method, which was applied to the upper basins of Bermejo and Pilcomayo Rivers (in the Upper Plata Basin), to estimate future trends in sediment yield. Projections for climate drivers (rainfall and temperature) were obtained through four regional climate models, with boundary conditions provided by three global climate models, for the period 2011–2100. Satellite imagery and gridded climate data were used to implement the sediment yield baseline scenario (1961–1990), which was calibrated based on solid discharge data. The model was used to determine projections of sediment yields, as time series of mean annual values for each basin. The analysis was performed on average for three-decadal periods, namely, the scenarios of ‘near future’ (2011–2040), for which current yields are essentially maintained; ‘intermediate future’ (2041–2070), where a reduction trend is detected; and ‘far future’ (2071–2100), with a recovery of yields, which even increase above the baseline scenario rate in the case of the Bermejo Upper Basin. [ABSTRACT FROM PUBLISHER]

This paper presents an analysis of the sediment dynamics that takes place at different scales within the Middle and the Lower Parana River in the La Plata Basin. The aim of this study is to provide a multi-disciplinary and multi-scale approach for the prediction of river future morphology in the context of climate change, the intended use of which is the prognosis of river morphodynamics’ long-term impact on manmade structures and activities over or near the river. The study is based on three levels of mathematical modelling, with the output of wider-scale models providing the input conditions for more specific ones. Climate models give the input ensemble, i.e. future precipitation and temperature over La Plata Basin. The semi-distributed macroscale variable infiltration capacity hydrological model simulates the flow discharge time series that are applied to an own-developed 1D morphodynamic model. The 1D model simulates future rate of sediment transport and corresponding bed-level changes at watershed scale and provides the boundary conditions for a 2D model. Therefore, streamflow divagations at channel scale are simulated by means of the MIKE21C code developed by the Danish Hydraulic Institute. The analysis indicates a rather low sensitivity of the Parana River bed profile, i.e. 1D morphology, to the increase predicted in flow discharge, whereas the streamflow appreciably divagates. In particular, surpassing an upper bound in the most frequent discharge appears effective in driving the actual bifurcated morphology into a meandering-multithread configuration. [ABSTRACT FROM PUBLISHER]

In this paper, the effects of land cover changes on the climate of the La Plata Basin in southern South America are investigated using the Weather and Research Forecasting (WRF) Model configured on a 30/10-km two-way interactive nested grid. To assess the regional climate changes resulting from land surface changes, the standard land cover types are replaced by time-varying Ecosystem Functional Types (EFTs), which is a newly devised land-cover classification that characterizes the spatial and interannual variability of surface vegetation dynamics. These variations indicate that natural and anthropogenic activities have caused changes in the surface physical parameters of the basin, such as albedo and roughness length, that contributed to regional climate changes. EFTs are obtained from functional attributes of vegetation computed from properties of the Normalized Difference Vegetation Index (NDVI) to represent patches of the land surface with homogeneous energy and gas exchanges with the atmosphere. Four simulations are conducted, each experimental period ranging from September to November in two contrasting years, 1988 and 1998. The influence of an identical EFT change on the surface heat fluxes, 2-m temperature and humidity, 10-m winds, convective instabilities and large-scale moisture fluxes and precipitation are explored for 1988 (a dry year) and 1998 (a wet year). Results show that the surface and atmospheric climate has a larger response to the same EFT changes in a dry year for 2-m temperature and 10-m wind; the response is larger in a wet year for 2-m water vapor mixing ratio, convective available potential energy, vertically integrated moisture fluxes and surface precipitation. For EFTs with high productivity and a weak seasonal cycle, the nearsurface temperature during the spring of 1988 and 1998 increased by as much as 1°C in the central and western portions of La Plata Basin. Additionally, for higher productivity EFTs, precipitation differences were generally positive in both dry and wet years, although the patterns are not uniform and exhibit certain patchiness with drier conditions. [ABSTRACT FROM AUTHOR]

Water resources management and agriculture planning models require a statistical synthesis of some rainfall features, in particular those representing dry atmospheric conditions. The bigger the basin, the more important these features become, as is the case of the La Plata Basin LPB.This paper focuses on the precipitation variability in the large LPB in South America, analysing the number of months per year with low rainfall and the sequences of months with low rainfall, their theoretical distributions and stability, which are needed as input for the models mentioned above.Long time series are used to analyse the lowfrequency variability and the relative importance of decadal variability. Changes are evident in the number of months per year with low rainfall, with a decrease of about 20 in the period after 1970.Theoretical distribution models binomial and geometric are fitted to these empirical distributions, and the regional variability of the fitting parameters is shown. In practically the entire region, the goodnessoffit of the two theoretical models considered is statistically satisfactory.The temporal variability of the parameters of the theoretical binomial p and geometric α distributions is analysed, in excluding subperiods of 10 and 5 years, respectively. The results show lowfrequency variability overlapped on a decadal variability, with low homogeneous regional behaviour.The distribution models have proven to be efficient for frequency adjustments of the rainfall properties studied. These results are an acceptable and necessary input to decision models in LPB. They also make it possible to infer effects of climate change. Copyright © 2008 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

We analyze the local and remote impacts of climate change on the hydroclimate of the Amazon and La Plata basins of South America (SA) in an ensemble of four 21st century projections (1970-2100, RCP8.5 scenario) with the regional climate model RegCM4 driven by the HadGEM, GFDL and MPI global climate models (GCMs) over the SA CORDEX domain. Two RegCM4 configurations are used, one employing the CLM land surface and the Emanuel convective schemes, and one using the BATS land surface and Grell (over land) convection schemes. First, we find considerable sensitivity of the precipitation change signal to both the driving GCM and the RegCM4 physics schemes (with the latter even greater than the first), highlighting the pronounced uncertainty of regional projections over the region. However, some improvements in the simulation of the annual cycle of precipitation over the Amazon and La Plata basins is found when using RegCM4, and some consistent change signals across the experiments are found. One is a tendency towards an extension of the dry season over central SA deriving from a late onset and an early retreat of the SA monsoon. The second is a dipolar response consisting of reduced precipitation over the broad Amazon and Central Brazil region and increased precipitation over the La Plata basin and central Argentina. An analysis of the relative influence on the change signal of local soil-moisture feedbacks and remote effects of Sea Surface Temperature (SST) over the Niño 3.4 region indicates that the former is prevalent over the Amazon basin while the latter dominates over the La Plata Basin. Also, the soil moisture feedback has a larger role in RegCM4 than in the GCMs. [ABSTRACT FROM AUTHOR]

Water resources availability presents a high degree of uncertainty in the context of climate change. In this study, the multi-year variability of simulated streamflow for three rivers (Paraná, Uruguay and Negro) in the La Plata Basin (LPB) in the period 1991–2098 is analysed. Simulated streamflow for that period were produced in a two-stage process involving a regional climate model (RCM) and a distributed hydrology model (VIC (variable infiltration capacity)). Outputs from two RCMs (PROMES [Spanish acronym for mesoscale forecast] and RCA [Rossby Centre regional atmospheric climate model]) were used in order to assess the sensitivity of the results to different models. Various spectral methods (singular spectrum analysis, maximum entropy method and multi-taper method) were used in order to detect low-frequency variability modes and preferred quasi-periodicities for annual and seasonal simulated time series. Both simulations generate larger runoff for the twenty-first century than those observed for the twentieth century for the three rivers. For annual time series, the variability in timescales longer than 30 years is detected by one of the simulations for the three rivers, and only weakly for the Negro River in the other. Seasonal variations of the preferred modes of multi-annual variability are apparent. The River Paraná shows a persistent 10-year period during most of the year in the PROMES-VIC simulation. No LFV modes were found for any trimester in any river for PROMES-VIC, while for RCA-VIC simulations, these appeared in austral summer (Negro and Uruguay rivers) or early winter (Paraná River). A striking finding, both for annual and seasonal simulated time series, is the conspicuous presence of pseudo-periods in the 2.5–5 years band that had already been captured in the observed 20th streamflow time series [Maciel, F., Díaz, A., and Terra, R., 2013. Multi-annual variability of streamflow in La Plata Basin. Part I: observations and links to global climate.International Journal of River Basin Management, 11 (4), 345–360.]. This pattern is probably linked to the El Niño–Southern Oscillation (ENSO) phenomenon. These results imply that the well-known relationships between ENSO and precipitation and streamflow anomalies in the LPB are expected to prevail during the twenty-first century. [ABSTRACT FROM PUBLISHER]

Distributions of monthly rainfall averaged spatially over three regions of the La Plata Basin (LPB) were projected for 2011–2040 and 2071–2100 using outputs of four regional climate models (RCMs) nested in three different general circulation models, run with the SRES A1B emission scenario. Tuning of simulations with observations was done at the control period 1981–1990. During the past 50 years, in part of LPB, there was a positive trend in annual precipitation. Two of the models indicate the maintenance of this trend over the northeast of Argentina and south of Brazil, while over the southernmost region of LPB, all models show increasing precipitation throughout the twenty-first century. Trends are less ambiguous for extreme precipitation, especially in the southernmost part of LPB, where huge and long-lasting floods take place over plains with small drainage. Months with extreme precipitation in LPB present a pronounced annual cycle with higher frequency from October to April. According to the RCM projections, this pattern would persist during the twenty-first century. Although, other factors cannot be discarded, the projected trends towards higher extreme monthly precipitation seem to be caused by an increase in the moisture convergence in the lower atmosphere over the east of LPB. [ABSTRACT FROM PUBLISHER]