Limnology and water quality in La Plata basin (South America) – Spatial patterns and major stressors

Abstract A sensitivity study of the impact of a groundwater scheme on hydrometeorological variables in coupled land–atmosphere simulations over southern South America is presented. It is found that shallow water tables in the groundwater scheme lead to reduced drainage and even upward capillary fluxes over parts of the central and southern La Plata basin. This leads to an increase in the simulated moisture in the root zone, which in turn produces an increase in evapotranspiration (ET) over the southern part of the domain, where ET is water limited. There is also a decrease in the near-surface temperature, in the range 0.5°–1.0°C. During the dry season, the increases in ET and relative humidity over the central La Plata coincide with an increase in precipitation downstream. Including groundwater leads to an increase in precipitation over parts of the central and southern La Plata basin during the early rainy season (October–December). The overall increase in ET and precipitation over the southern La Plata basin during the early rainy season is 13% and 10%, respectively. The additional precipitation comes from both an increase in the availability of atmospheric moisture when the groundwater scheme is used and its effect on the atmospheric instability. In the La Plata basin, including a representation of groundwater increases simulated precipitation and partially alleviates a warm and dry bias present in simulations without realistic subsurface hydrology.

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Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability

Annales Geophysicae ◽

10.5194/angeo-27-645-2009 ◽

2009 ◽

Vol 27 (2) ◽

pp. 645-657 ◽

Cited By ~ 29

Author(s):

G. A. M. Silva ◽

T. Ambrizzi ◽

J. A. Marengo

Keyword(s):

South America ◽

South American ◽

The South ◽

Trade Winds ◽

La Plata ◽

The Andes ◽

La Plata Basin ◽

Normal Frequency ◽

Rainfall Anomalies ◽

Low Level Jet

Abstract. The differences on the phase and wavelength of the quasi-stationary waves over the South America generated by El Niño (EN) and La Niña (LN) events seem to affect the daily evolution of the South American Low Level Jet east of the Andes (SALLJ). For the austral summer period of 1977–2004 the SALLJ episodes detected according to Bonner criterion 1 show normal to above-normal frequency in EN years, and in LN years the episodes show normal to below-normal frequency. During EN and LN years the SALLJ episodes were associated with positive rainfall anomalies over the La Plata Basin, but more intense during LN years. During EN years the increase in the SALLJ cases were associated to intensification of the Subtropical Jet (SJ) around 30° S and positive Sea Level Pressure (SLP) anomalies over the western equatorial Atlantic and tropical South America, particularly over central Brazil. This favored the intensification of the northeasterly trade winds over the northern continent and it channeled by the Andes mountain to the La Plata Basin region where negative SLP are found. The SALLJ cases identified during the LN events were weaker and less frequent when compared to those for EN years. In this case the SJ was weaker than in EN years and the negative SLP anomalies over the tropical continent contributed to the inversion of the northeasterly trade winds. Also a southerly flow anomaly was generated by the geostrophic balance due to the anomalous blocking over southeast Pacific and the intense cyclonic transient over the southern tip of South America. As result the warm tropical air brought by the SALLJ encounters the cold extratropical air from the southerly winds over the La Plata basin. This configuration can increase the conditional instability over the La Plata basin and may explain the more intense positive rainfall anomalies in SALLJ cases during LN years than in EN years.

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Effects of a Groundwater Scheme on the Simulation of Soil Moisture and Evapotranspiration over Southern South America

Journal of Hydrometeorology ◽

10.1175/jhm-d-16-0051.1 ◽

2016 ◽

Vol 17 (11) ◽

pp. 2941-2957 ◽

Cited By ~ 11

Author(s):

J. Alejandro Martinez ◽

Francina Dominguez ◽

Gonzalo Miguez-Macho

Keyword(s):

South America ◽

Land Surface ◽

Climate Model ◽

Soil Column ◽

Water Storage ◽

Surface Model ◽

Southern South America ◽

La Plata ◽

Continental Scale ◽

La Plata Basin

Abstract The effects of groundwater dynamics on the representation of water storage and evapotranspiration (ET) over southern South America are studied from simulations with the Noah-MP land surface model. The model is run with three different configurations: one including the Miguez-Macho and Fan groundwater scheme, another with the Simple Groundwater Model (SIMGM), and the other with free drainage at the bottom of the soil column. The first objective is to assess the effects of the groundwater schemes using a grid size typical of regional climate model simulations at the continental scale (20 km). The phase and amplitude of the fluctuations in the terrestrial water storage over the southern Amazon are improved with one of the groundwater schemes. An increase in the moisture in the top 2 m of the soil is found in those regions where the water table is closer to the land surface, including the western and southern Amazon and the La Plata basin. This induces an increase in ET over the southern La Plata basin, where ET is water limited. There is also a seasonal increase in ET during the dry season over parts of the southern Amazon. The second objective is to assess the role of the horizontal resolution on the effects induced by the Miguez-Macho and Fan groundwater scheme using simulations with grid sizes of 5 and 20 km. Over the La Plata basin, the effect of groundwater on ET is amplified at the 5-km resolution. Notably, over parts of the Amazon, the groundwater scheme increases ET only at the higher 5-km resolution.

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A New Look at the Identification of Low-Level Jets in South America

Monthly Weather Review ◽

10.1175/mwr-d-17-0237.1 ◽

2018 ◽

Vol 146 (7) ◽

pp. 2315-2334 ◽

Cited By ~ 8

Author(s):

Maurício I. Oliveira ◽

Ernani L. Nascimento ◽

Carolina Kannenberg

Keyword(s):

South America ◽

Numerical Data ◽

Southeastern Brazil ◽

La Plata ◽

Low Level ◽

La Plata Basin ◽

Low Level Jets ◽

Forcing Mechanisms ◽

Definition Of ◽

Environmental Prediction

Abstract Criteria currently employed in algorithms that identify low-level jets (LLJs) in South America utilizing rawinsonde and gridded model data fail to detect an important number of LLJ events. This study discusses shortcomings in the existing approaches for LLJ identification in South America and proposes modifications to the criteria regarding layer depth for LLJ identification and wind direction. Episodes of southerly LLJs, which have received less attention in the La Plata basin, are also included in the investigation. A sensitivity analysis of LLJ detection in South America upon the choice of the criteria applied to a sample period of 15 years (1996–2010) of gridded numerical data from the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR), and to a 20-yr dataset (1996–2015) of actual rawinsondes for the La Plata basin, reveals the benefits of revising the criteria. The modified criteria allow for the characterization of a wider spectrum of LLJs over key regions of South America, such as over the Bolivian–Paraguayan border, Sierras de Córdoba in Argentina, and southern-southeastern Brazil. This wider range of events includes elevated LLJs, mostly with strong zonal components, that account for approximately 20% of the full sample of LLJs identified in the rawinsonde dataset investigated here. The revised criteria have the advantage of retaining the identification of episodes that meet the consecrated definition of the South American LLJ, while at the same time providing an augmented sample of such wind systems. Our results provide further insights into the forcing mechanisms of distinct types of LLJs in South America, ranging from topographic to baroclinic effects.

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