Ramiro I. Saurral

Land use impact on the Uruguay River discharge

[1]xa0The Uruguay River basin experienced extensive land use change during the second half of the twentieth century as a result of expansion of agricultural area, while streamflow and precipitation increased during the same period. This study assesses the impact of land use change between 1960 and 2000 on streamflow using a hydrology model that explicitly accounts for the role of land cover. Although the model suggests that land use change could have large effects on streamflow, changes in mean streamflow are attributable to climatic variations and not to land cover change. On the other hand, a faster runoff response to precipitation was observed toward the end of the period, which does appear to be attributable to land cover change. Overall, however, the positive trend observed in the Uruguay River streamflow during the second half of the past century should be attributed to increased precipitation, rather than land cover change.

Parana River morphodynamics in the context of climate change

ABSTRACT 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.

Hydrological projections of fluvial floods in the Uruguay and Paraná basins under different climate change scenarios

Hydrological modelling with climate scenario data are used to develop projections of changes in frequency and duration of flood events in the margins of the lower sections of the Paraná and Uruguay Rivers in La Plata Basin for the twenty-first century. Discharges were simulated with the Variable Infiltration Capacity hydrologic model considering the statistically bias corrected daily maximum and minimum temperatures and rainfall outputs from five regional climate models and different emission scenarios. Results show that although it is expected that compared to the current conditions the temperature would rise and precipitation would have a slight increase in La Plata Basin during the present century, more frequent and lasting fluvial flooding events in the lower Paraná and Uruguay basins could be expected. However, the range of results derived from different climate models though consistent in sign, indicate that the uncertainty is large.

Assessment of climate change on the future water levels of the Iberá wetlands, Argentina, during the twenty-first century

The Iberá wetlands, located in La Plata Basin, is a fragile ecosystem habitat of several species of flora and fauna and it also constitutes one of the largest inland freshwater of the world. In this study, the hydroclimatologic response to projected climatic changes in the Iberá wetlands is assessed. Bias corrected temperature and precipitation data from four Regional Climate Models (RCMs) developed for the CLARIS-LPB project were used to drive the calibrated variable infiltration capacity (VIC) hydrological model for different time slices. Derived future scenarios consist on changes in temperature, precipitation and water level of the Iberá Lake for the periods 2021–2040 and 2071–2090 with respect to present. All RCMs are consistent in predicting a warming for the near future (0–2°C) and also to the end of the century (1.5–4.5°C) in the study region, but differ in the sign and percentage of precipitation changes. VIC modelling results suggest that the Iberá Lake level could increase in the twenty-first century and that this increment would be higher in the summer months. Nevertheless, the projected 10 cm of water-level increase could be not so relevant as it is of the same order of magnitude than the observed interdecadal variability of the system.

Development of statistically unbiased twenty-first century hydrology scenarios over La Plata Basin

Abstract There is an increasing demand for future climate scenarios, particularly for impact studies. In this study, simulation outputs taken from a set of three regional climate models (RCMs) are used to force a hydrologic model to derive future streamflow scenarios for La Plata Basin. As RCMs have biases in their mean precipitation and temperature fields, a statistical scheme is previously used to remove the systematic part of the bias. Future hydrologic scenarios were derived considering two future periods: 2021–2040 (near future) and 2071–2090 (far future). In terms of climate projections, RCMs predict warmer conditions in almost the whole basin, while precipitation variations are not uniform in sign across the region but overall tend to be positive over the southern part of the basin. Nevertheless, a trend towards a gradual increase in streamflow was found for the majority of the rivers in the basin particularly for the near future followed by less uniform variations towards the end of the present century. Future changes in the largest monthly streamflow are similar to those in the mean values, with also some differences among RCMs and on the period and sub-basin considered.

Observed modes of sea surface temperature variability in the South Pacific region

The South Pacific (SP) region exerts large control on the climate of the Southern Hemisphere at many times scales. This paper identifies the main modes of interannual sea surface temperature (SST) variability in the SP which consist of a tropical-driven mode related to a horseshoe structure of positive/negative SST anomalies within midlatitudes and highly correlated to ENSO and Interdecadal Pacific Oscillation (IPO) variability, and another mode mostly confined to extratropical latitudes which is characterized by zonal propagation of SST anomalies within the South Pacific Gyre. Both modes are associated with temperature and rainfall anomalies over the continental regions of the Southern Hemisphere. Besides the leading mode which is related to well known warmer/cooler and drier/moister conditions due to its relationship with ENSO and the IPO, an inspection of the extratropical mode indicates that it is associated with distinct patterns of sea level pressure and surface temperature advection. These relationships are used here as plausible and partial explanations to the observed warming trend observed within the Southern Hemisphere during the last decades.

The Climate-System Historical Forecast Project: Providing Open Access to Seasonal Forecast Ensembles from Centers around the Globe

AMERICAN METEOROLOGICAL SOCIETY | NOVEMBER 2017 UNCERTAINTY IN SEASONAL FORExad CAST ING. Any prediction of the future evolution of the Earth system requires an associated assessment of its uncertainty. This is true whether the forecast is for the days ahead or is a longer-term prediction for the following months and seasons. For seasonal forecasts, the uncertainty associated with inexact initial conditions, which can grow rapidly in time, is usually addressed by running multiple forecasts with perturbations applied to the initial state of the ocean and atmosphere (Arribas et al. 2011; Stockdale et al. 2011). The idea is that the perturbed initial conditions are of a suitable magnitude to represent the uncertainty in the observational measurements and the analysis tools that are used to process them. As the forecast evolves, the differences between the forecasts, known as the ensemble “spread,” should therefore reflect the typical forecast error, or “uncertainty”; in other words, the eventual real-world evolution should be contained within the cluster of this forecast ensemble. In tandem, uncertainty in forecasts is also contributed to by our inexact representations of the Earth system physics. This contribution to uncertainty is sampled by employing different Earth system models (Yun et al. 2005; Weisheimer et al. 2009; Smith et al. 2013), the so-called multimodel approach, which is often supplemented by the use of perturbations to physical processes, known as stochastic physics schemes, to further account for structural errors in a particular The Climate-System Historical Forecast Project

Multi-annual variability of streamflow in La Plata Basin. Part II: simulations for the twenty-first century

ABSTRACT 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.