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The annual amount of precipitation inputs received by a site during a full year is considered a dominant spatial and temporal control of primary productivity and other related process in arid to subhumid ecosystems. However, to be effectively used by plants, these inputs have to escape runoff, favoured by large and less frequent precipitation events, and evaporation losses, favoured by small and more frequent events. Thus, available water for plant transpiration is not only influenced by the annual sum of precipitation events but also by their frequency-size distribution. In this paper, we characterize this distribution and its association to total annual precipitation inputs through space (five sites along a tenfold precipitation gradient across 1000 km) and time (1961-2010) in the plains of central Argentina. We decomposed total precipitation into two structural components, which are the frequency and mean size of events, showing that they have similar contributions (log-log slopes ≈ 0·5) explaining precipitation shifts in space. Over time, however, we found a preponderance of mean event size explaining precipitation fluctuations, particularly towards wetter sites (log-log slopes increasing from 0·61 to 0·88). The relative variability of event sizes, independent of their mean size (i.e. inequality), was numerically characterized with Gini coefficients derived from Lorenz curves, which showed highly constant values in space and time. Assuming fixed event-size thresholds for evaporation and runoff, and ignoring other controls beyond precipitation structure, the proportion of water potentially available for plant transpiration grew with total precipitation, raising from 0·45 to 0·71 from the driest to the wettest sites, but displaying stronger responses to total precipitation in time, particularly in drier sites. No long-term trends in any of the precipitation structure variables were detected. Response functions of frequency and mean size of events to annual precipitation together with Lorenz curves appeared to be robust descriptors of precipitation regimes that, not requiring any a priori assumptions, are useful to assess how spatial and temporal shifts in total precipitation may concurrently affect its relative availability for plant transpiration. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper studies the climatic conditions of warm and cold dry months in the humid and semi-humid Argentine region and some aspects of the regional circulation related to these cases. The climatic analysis of warm (temperatures above percentile 80) and cold (temperatures below percentile 20) dry months is based on precipitation and temperature data registered at reference stations over a period of at least 70 years, while the associated circulation is derived from daily data of geopotential height at 500 hPa from NCEP-DOE Reanalysis 2 database. The reference station for the center of the country registered a greater number of warm dry months during both the warm season (October-March) and the cold season (April-September), whereas the reference stations in the north-east and center-east showed differences depending on the time of the year, with more cold dry months during the April-September season and more warm dry months in the October-March season. A classification of daily fields of geopotential height anomalies at 500 hPa was used to analyze the atmospheric circulation related to warm and cold dry months. The circulation patterns were obtained by applying principal component analysis and cluster analysis. Findings show that some mid-level circulation patterns occur with a significant different frequency during the warm dry months or the cold dry months studied. Finally, cases of spatially extended precipitation-deficit conditions (hereinafter generalized droughts) were studied, noting dominant patterns that are coherent with the previous results. [ABSTRACT FROM AUTHOR]

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This paper gives an account of the assessment and quantification of the water balance and the hydrogeological processes related to lake-groundwater interaction in the Pampa Plain by using hydrogeochemical, isotopic and flow numerical modeling techniques. La Salada is a permanent shallow lake, with an area of 5.8 km, located on the SE of Buenos Aires Province. A total of 29 lake water samples and 15 groundwater samples were collected for both hydrochemical analysis and environmental stable isotope determination. Water table depths were measured in wells closed to the lake. Groundwater samples appear grouped on the Local Meteoric Water Line, suggesting a well-mixed system and that rainfall is the main recharge source to the aquifer. Water evaporation process within La Salada is also corroborated by its isotopic composition. The model that best adjusts to La Salada Lake hydrochemical processes includes evaporation from groundwater, calcite precipitation with CO release and cationic exchange. The annual water balance terms for the lake basin indicates for each hydrological component the following values: 1.16 E m rainfall, 8.15 E m evapotranspiration, 1.90 E m runoff, 1.55 E m groundwater recharge, 6.01 E m groundwater discharge to the lake, 9.54 E m groundwater discharge to the river, 5.00 E m urban extraction and 4.90 E m lake evaporation. Integrated analysis of hydrochemical and isotopic information helped to calibrate the groundwater flow model, to validate the conceptual model and to quantitatively assess the basin water balance. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper focuses on the historical range of variability of landslide activity and its relation to climate in the Aconcagua Park, Argentina. Landslide frequency data are obtained through historic compilation, including the review of more than 85 data sources and personal interviews with members of the local community. Based on these records, the study analyzes major landslide triggering mechanisms and evaluates the role of climate. Slope instability in Aconcagua Park appears to be mainly forced by the melting of snow accumulated during the winter season, which in turn promotes soil saturation and landslide occurrence the following spring-summer (December-February). This finding is supported by a strong correlation between landslides and stream flows of Andean rivers. These peaks occur during warmer seasons, fed by snow and ice-glacier melting. In contrast, the correlation between landslide frequency and precipitation (diary/accumulative/monthly/annual) is less certain; and the relationship of landslide to temperature records (mean annual temperature/mean temperature during November-February period) is weak. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The study of the temporal-spatial variability of dry sequences and the probability of their occurrence are particularly important in understanding the impact of climate change on droughts. This paper analyses the different properties of dry sequences, focussing on extreme condition, analysing their degree of spatial coherence, and their temporal variability. For the study, daily precipitation data are used for the period 1961-2000 throughout Argentina. The region north of 40°S is divided in two from the meridian of 63°W with highly differentiated 'dry' properties. The eastern region is more homogeneous where mean dry sequences last less than six days and long sequences of about 60 days. The Andean region shows a marked east-west gradient in any of the above properties, with extreme values of over 10 days (mean sequences) and 150 days (the longest sequences). At the seasonal level the above properties reflect a differential pattern according to the time of year under study. In the case of summer, when the dry sequences can be more harmful to crops, the maximum duration in the Pampa region can extend to about 25 days. Owing to the problems that dry sequences of over 30 days can produce in the different ecosystems and based on the above findings, the temporal-spatial variability is analysed, and a variability over the years, together with a progressive decrease in the occurrence of such events, is found. The study of extreme dry events provides useful tools that can be applied to different hydrological and agricultural needs. Furthermore, our climatological findings help validate climate models. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The present paper describes the quality-control component of an automatic procedure (APACH: A Procedure for Automated Quality Control and Homogenization of Weather Station Data) developed to control quality and homogenize the historical daily temperature and precipitation data from meteorological stations. The quality-control method is based on a set of decision-tree algorithms analyzing separately precipitation and minimum and maximum temperature. All our tests are non-parametric and therefore are potentially useful in regions or countries presenting different climates as those observed in Argentina. The method is applied to the 1959–2005 historical daily database of the Argentine National Weather Service. Our results are coherent with the history of the Weather Service and more specifically with the history of implementation of systematized quality control processes. In temperature, our method detects a larger number of suspect values before 1967 (when there was no quality control) and after 1997 (when only real-time quality control had been applied). In precipitation, the detection of error in extreme precipitations is complex, but our method clearly detected a strong decrease in the number of potential outliers after 1976 when the National Weather Service was militarized, and the network was strongly reduced, focusing more on airport weather stations. Also in precipitation, we analyze in detail the long dry sequences and are able to identify potential long erroneous sequences. This is important for the use of the data for hydrological or agricultural impact studies. Finally, all the data are flagged with codes representing the path followed by the record in our decision-tree algorithms. While each code is associated to one of the categories (“Useful”, “Need-Check”, “Doubtful” or “Suspect”), the final user is free to redefine such category-assignment. [ABSTRACT FROM AUTHOR]

The goal of the present paper is to determine, from a spatial and temporal perspective, the distribution patterns of drought, obtaining areas of extreme hydrological risk in the departments of the Buenos Aires province (Argentina). The hydrologic constants (Field Capacity and Permanent Wilting Point) are analyzed and a synthesis map elaborated. Then, the relationship with data from agricultural emergencies caused by drought is established. As drought is highly related to climate variability and its influence over soils, an analysis which might allow to identify temporal and spatial patterns of drought and so risk areas is considered hereby relevant. The obtained results show the drought-affected areas distributed by department, the relationship with the hydrologic constants and their risk with respect to the analyzed event. The present paper belongs to the research project: "Water , development and uncertainty. The reduction of availability a paradigm of inequity" which is in process at UNLP-FAHCE-CIG since 2008. [ABSTRACT FROM AUTHOR]

The snowpack in the central Andes (30°–37°S) is the primary source for streamflow in central Chile and central-western Argentina, but few published studies are available on snowpack variability in the region. This paper develops the first regional snowpack series (1951–2005) from Chilean and Argentinean snow course records. This series shows a strong regional signal, marked interannual variability, and a positive, though nonsignificant, linear trend. Correlations with local precipitation and temperature records reveal a marked association with conditions in central Chile. High snow accumulation is generally concurrent with El Niño events in the tropical Pacific, but only 5 of the 10 driest years coincided with La Niña events. Evaluation of 500-hPa geopotential height anomaly maps during extreme snow years highlights the crucial significance of tropospheric conditions in the subtropical and southeast Pacific in modulating snowfall. Correlations with gridded SST and SLP data and multiple regressions with large-scale climatic indices corroborate a Pacific ENSO-related influence largely concentrated during the austral winter months. This hampers the predictability of snowpack before the onset of the cold season. Annual and warm-season river discharges on both sides of the cordillera are significantly correlated with the regional snowpack record and show positive linear trends over the 1951–2004 common period, probably related to a greater frequency of above-average snowpacks during recent decades. Future demand and competition for water resources in these highly populated regions will require detailed information about temporal and spatial variations in snow accumulation over the Andes. The results indicate that the relationships between snowpack and atmospheric circulation patterns prior to the winter season are complex, and more detailed analyses are necessary to improve prediction of winter snowfall totals. [ABSTRACT FROM AUTHOR]

There is a widely held view that the Pampa region (PR) dry and wet periods are predominantly a consecuence of the El Niño-Southern oscillation (ENSO) phenomenom. The current paper focuses on non-ENSO rainfall anomalies for the period 1948–2000, the more recent of which have had catastrophic consequences throughout the region. We analyze horizontal water vapor transport, pressure and circulation anomalies occurring in Southern South America (SSA) during this type of event. Positive and negative (wet and dry) extreme events during the rainy and dry seasons in the region were registered. Based on NCEP reanalysis data it was established that under rainfall deficit, anomalies of similar intensity occurred simultaneously in the PR and in central Chile, whereas under excess rainfall the anomalies were mostly confined to the PR. The existence of a cyclone-anticyclone pair in the anomalous circulation pattern over mid latitudes of the Atlantic and Pacific oceans and straddling the southern portion of the continent maintains an intense and extense meridional circulation over the continental plains, which leads to the abnormal values in moisture transport and rainfall rate. The atmospheric water balance equation calculated for the PR indicates that anomalous water vapor is carried in from the continental equatorial region and from the subtropical Atlantic, its magnitude varying in accordance with the season and the sign of the anomaly. Furthermore, evidence of the important role of transient terms corroborates their contribution to the anomalous total moisture flux divergence under rainfall deficit during the dry season. The mean sea-level pressure anomaly fields of the extreme cases were further examined by principal component analysis to discern those circulation features directly linked to rainfall deviations. [ABSTRACT FROM AUTHOR]

The aim of this paper was to find a synergism between maximum solar activity and rains in Azul, Buenos Aires (36°45' S, 59°57' W and altitude. 137 m ), using a series of annual rainfalls from 1913 to 2012. The results showed that the last four solar activity maxima correspond to the years of highest rainfall. Annual rainfalls for those years recorded on average 1317mm (2.4 standard deviation above the mean), which was significantly different from the mean of the last hundred years (855.7mm ±191.1 mm). A positive relationship between years of maximum solar activity and the occurrence of extreme rainfall events that generate excess water and flooding in the rural and urban sectors of Azul was found. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper is to present the partial trends of rainy days and total precipitation in Córdoba Province, Argentina, during the period 1960–2010 and the full range of precipitation for the Córdoba Observatory station, which has the longest measurement record in Argentina, 1873–2010, and to show the relationship between these variables and solar activity. A strong association is shown between break points when the trend changes for both the number of rainy days and the total precipitation, and the occurrence of maxima in the sunspot cycle, indicating that these variables are modulated by the solar Hale cycle and probably by the influence of cosmic rays. [Copyright &y& Elsevier]

The Chaco plain region in Argentina is located in the north of the country and east of Los Andes where the main activity is the agriculture. As such activity is highly affected by interannual rainfall variability, the influence of some of the principal atmospheric and oceanic forcing is investigated in this paper. Results show that the factors which affect precipitation highly depend on the season and the subregion. The position of the South Atlantic Height and the sea surface temperature in the coast of southern Brazil and Buenos Aires seem to be the factors that affect rainfall, all over the year. The El Niño-Southern Oscillation phenomenon affects summer and spring rainfall and the Southern Annular Mode involves spring precipitation but both only in the east of the study region. Furthermore, enhanced convection in Central Brazil, mainly influences autumn and spring rainfall. [ABSTRACT FROM AUTHOR]

Summary: In recent times, significant areas of the Northeastern Argentine (NEA) have been affected by climatic fluctuations which have caused serious damages in ecosystems and people’s livehoods, both by floods and droughts. This has mainly occurred in the Santa Fe Province, having a great impact on the underlying unconfined aquifer. This paper analyzes the relationships between meteorological variability and water table levels in the context of climate variability and climatic change in the lower Carcarañá river experimental basin (about 4700km2), located in the Santa Fe Province. The goal of the study is to obtain long-term (interannual) predictions of water table levels in the region. The methodology used responds to a hypothetical conception of the temporal series having a signal formed by random components with characteristics of white noise. Singular Spectral Analysis (SSA), among other non-parametric techniques were used to identify fluctuations and trend changes in climatic time-series. These characteristics provide valuable information for the evaluation of climatic evolution and for the detection of variations in this evolution, suggesting a climatic change either by natural mechanisms or by anthropogenic impacts. A positive trend in precipitation is found throughout the studied region with water table levels showing a similar spatial–temporal behavior. The SSA gives significant periodicities between 3 and 8years showing a possible link between El Niño-Southern Oscillation (ENSO) phenomenon and precipitation and water table levels. The periodicities linked with ENSO are always present and the structures of the series are similar for the different studied periods. The results obtained, even if they are experimental constitute a first approximation. In general, they are promising, since the generated basis will enable to face further and more complex stages. [Copyright &y& Elsevier]

Abstract: Conventional surface data and quantitative estimations of precipitation are used to document the occurrence and spatial distribution of severe weather phenomena associated with deep moist convection over southeastern South America. Data used in this paper are 24-hour rainfall, maximum hourly gusts and present weather reports from the surface station network for Argentina to the north of 40°S and cover the period 2000–2005. Hourly rainfall estimated with the CMORPH technique (CPC MORPHing technique, R. J. Joyce et al., 2004) is included in the analysis in order to increase the density of the precipitation database from January 2003 to December 2005. Extreme events are detected by means of a 95th-percentile analysis of the 24-hour rainfall and wind; values greater than 30mm and 25ms−1 respectively are considered extreme in the study area. These results are related to the presence of deep convection by considering the 235K and 218K cloud shield evolution in Geostationary Operational Environmental Satellite-12 Infrared (GOES-IR) imagery evaluated by the Forecasting and Tracking of Cloud Cluster (FORTRACC) technique. Rainfall above 30mmday−1 and present convection-related weather events tend to occur in the northeast of the country. Finally, an analysis is made of the relationship between severe phenomena and the location and lifecycle of Mesoscale Convective Systems (MCSs) defined by the 218K or 235K levels. According to the reports, favorable locations for severe weather concentrate to the northeast of the cloud shield anvil centroid although most of the cases are found in the northwest. This feature can be seen in systems with anvil areas larger than 250,000km2 in association to the predominant mid-level wind shear direction from the northwest over the area. Moreover, systems with centers located north of 30°S present a more circular shape while those to the south are more elongated with a NW–SE main axis clearly related to the presence and interaction with frontal zones over the area. Most of the events occur previous to the moment when the systems reach their maximum extension, between 2 and 10h after the initiation of the system depending on the size of the MCSs. [Copyright &y& Elsevier]

Abstract: This paper presents PWV estimates from GPS data computed at four continuously operated GPS stations in Argentina established at Buenos Aires, Córdoba, Rosario and Salta over a 1 year period (2006–2007). The objective is to analyze the behaviour of the GPS PWV estimation using mean tropospheric temperature () values from the Bevis model, Sapucci model and obtained by a numerical integration of variables provided by the operational analysis of the National Centre of Environmental Prediction (NCEP). The results are validated using PWV values from nearest radio soundings. Moreover, a comparison between PWV values determined from microwave sensors deployed on the NOAA-18 satellite and PWV from GPS observations is also presented. From the analysis we can see that the computation of GPS PWV using the from the Bevis model, originally deduced for the northern hemisphere, shows similar behaviour to the respective computation using a Sapucci model inside 0.5mm. The differences between the T m values computed from the Sapucci model and the numerical integration of NCEP variables are of the order of 15K, although it does not represent a significant error in PWV. Nevertheless, differences in bias are imperceptible during the dry period and they are as big as 3mm during the moist or high precipitation period. This behaviour could not represent an improvement when comparing radio soundings with respect to the GPS PWV values using different estimations of T m . Thus, we conclude that the usage of T m estimated from the Bevis model is the best choice for regional studies, considering the simplicity and dissemination of the method, unless some more studies taking into account the geographical and climatological characteristic of the region are performed. As expected, GPS PWV values show very good agreement with radio sounding determinations, small differences can be observed especially during extreme precipitation periods. In general the NOAA PWV values denote an over estimation of the available water vapour. It is important to note that the determination of PWV is not the mean product of the NOAA-18 satellite mission. These results show the potential of such a product although a preliminary calibration using GPS PWV is still necessary. [Copyright &y& Elsevier]

Seasonality in Argentina is examined using precipitation observations from 56 weather stations north of 42°S and CRU gridded precipitation. The Walsh and Lawler Seasonality Index (SI) and Precipitation Concentration Index (PCI) are calculated to determine the different seasonality regimes. The main characteristic is an eastwest gradient, where precipitation tends to be more evenly distributed throughout the different months of the year in the east while rainfall in the west is concentrated in 3 months or less. High replicability values indicate that the wettest month generally occurs during a same period of months in central and northern Argentina. Several stations in eastern humid Argentina have significant positive changes in the mean of seasonality indices between 1961 and 1985 and 1986 and 2010, and increasing trend. In most cases this leads to a change in the regime from rather seasonal with a short dry season to a seasonal regime. Through a PAM Clustering technique a new regionalization of precipitation seasonality is obtained. The mean series in each cluster show a tendency towards more seasonal and highly seasonal regimes in all regions. The SI and PCI indices were calculated using the precipitation outputs of 18 global climate models (GCMs) from the Coupled Model Inter‐comparison Project Phase 5 (CMIP5) to examine the ability of these models to represent seasonality spatial distribution and changes in Argentina. To some extent the spatial distribution of seasonality is captured by models; however, there are considerable discrepancies in the location and extension of the eastwest gradient. The sign and location of trends and changes in the mean SI and PCI are adequately reproduced in only a few models. The low ability of GCMs to represent seasonality and its changes is a consequence of the difficulties GCMs have simulating precipitation characteristics in Argentina reported by different authors. [ABSTRACT FROM AUTHOR]

Planform drainage reorganization in catchments is a common response to changes in boundary conditions. Rivers reorganize through two predominant mechanisms: discrete stream capture events and progressive divide migration. Using general geomorphic observations, flow azimuth analysis, χ anomalies, local headwater relief, and the normalized steepness index (ksn), we examine drainage reorganization, its potential controls, and the response timescales for drainages in the Sierra de las Planchadas, NW Argentina. We additionally expand on the comparison of trunk and tributary ksn values as a potential tool for recognizing drainage reorganization. We identify three significant patterns of reorganization: (1) the migration of the main drainage divide (MDD) toward the hinterland, (2) capture of longitudinal drainages by transverse reaches, and (3) shrinking foreland catchments that will result in changes to basin outlet spacing. We determine that the migration of the MDD is due to local base level differences between the major range‐bounding basins, while more local patterns, such as the capture of longitudinal drainages, are the result of the distribution of erosionally resistant lithologies. We additionally assess the response timescales required for topologic changes to the drainage network, such as divide migration; we conclude that, as suggested by modeling studies, they are longer than the timescale required for channel profile adjustment. Key Points: Base level differences across a range can cause drainage reorganization without uplift or precipitation gradientsLithology controls local patterns of reorganization and the likelihood of stream capture eventsHigh values of normalized steepness in trunk channels, but not tributaries, are indicative of area gain through stream captures [ABSTRACT FROM AUTHOR]

ABSTRACT: It is generally agreed that models that better simulate historical and current features of climate should also be the ones that more reliably simulate future climate. This article describes the ability of a selection of global climate models (GCMs) of the Coupled Model Intercomparison Project Phase 5 (CMIP5) to represent the historical and current mean climate and its variability over northeastern Argentina, a region that exhibits frequent extreme events. Two types of simulations are considered: Long‐term simulations for 1901–2005 in which the models respond to climate forcing (e.g. changes in atmospheric composition and land use) and decadal simulations for 1961–2010 that are initialized from observed climate states. Monthly simulations of precipitation and temperature are statistically evaluated for individual models and their ensembles. Subsets of models that best represent the region's climate are further examined. First, models that have a Nash–Sutcliffe efficiency of at least 0.8 are taken as a subset that best represents the observed temperature fields and the mean annual cycle. Their temperature time series are in phase with observations (r > 0.92), despite systematic errors that if desired can be corrected by statistical methods. Likewise, models that have a precipitation Pearson correlation coefficient of at least 0.6 are considered that best represent regional precipitation features. GCMs are able to reproduce the annual precipitation cycle, although they underestimate precipitation amounts during the austral warm season (September through April) and slightly overestimate the cold season rainfall amounts. The ensembles for the subsets of models achieve the best evaluation metrics, exceeding the performance of the overall ensembles as well as those of the individual models. [ABSTRACT FROM AUTHOR]

Different rainfall parameters are analysed in the present work in order to describe precipitation in three Argentine reference stations. These locations represent their precipitation climate region through a centenary data record. The selected parameters are annual accumulated precipitation, number of days with precipitation and precipitation intensity. All three stations indicate a positive trend in the first two variables over the studied period; moreover, because of a proportional increase, the precipitation intensity parameter has no significant variability. From the analysis of these variables and applying statistical methods, a climatic jump is found in each station, around the 1950s. A second focus of this work is the analysis of rain spells. To this end, a cutoff value for each station is found and used so as to establish the relationship between the accumulated precipitation and the frequency of rain spells per year. The total number of rain spells follows an exponential decay function for their relative frequency, considering the number of days that constitutes them. Rain spell characterisation allows for the understanding of their contribution to precipitation, according with its duration. [ABSTRACT FROM AUTHOR]

Pampean lakes are characterised by the alternation of flood and drought periods, but little is known about its effects on fish assemblage in an extended temporal scale. This study analyses the temporal variability of the fish assemblage in Chascomús Lake, and discusses the role of temperature and precipitation as potential drivers of fish composition shifts. Data acquisition was based on experimental fishing performed from 1999 to 2013 and from historical fishing records. Two alternative fish assemblage configurations were identified by cluster analysis. Odontesthes bonariensis, Parapimelodus valenciennis and Cyphocharax voga were the dominant species, which accounted for 70-80% of the relative abundance. The species O. bonariensis showed temporal fluctuations in its representativeness, changing from dominant to almost absent, whereas C. voga and P. valenciennis changed their abundance following a similar pattern along time. When historical data were considered, Platanichthys platana appeared as the fourth most relevant species. Precipitation, critical temperatures and fish mortalities were identified as the main drivers of species abundance shifts. This study highlights the importance of long-term assessments to understand the influence of climatic factors and the need to maintain or restore natural ecological processes as the basis to support dynamic sustainable fisheries in Pampean shallow lakes. [ABSTRACT FROM AUTHOR]

Drought episodes during the early–mid 20th century were recognized and described in several places around the world, with extreme dry conditions and widespread landscape denudation, like during the famous ‘Dust Bowl’ in North America. However, there is scant documentation of droughts in southern South America, particularly from the Pampas, and none based on the geological record. In this article, we provide clear evidence of aeolian reactivation and sand deposition in some areas of La Pampa and San Luis provinces, western Pampas (Argentina), during early–mid 20th century in response to drier conditions, probably amplified, like historic droughts in North America, by anthropogenic factors (e.g. significant population increase and agriculture expansion into a fragile environment). Evidence includes widespread bare sand blowouts, extensive surfaces with active sand migration, steep dune lee slopes, and sharp crests covered by weak soil development (A/C profile), accompanied by historical documents. Optically stimulated luminescence (OSL) ages on aeolian beds confirm mobilization and sedimentation by wind processes c. 95–60 yr BP. Considering the dominant (over 70%) austral spring–summer precipitation, it is possible the rainfall deficit in western Pampas was linked to positive sea surface temperature (SST) anomalies in the western subtropical South Atlantic Ocean (20–30°S and 30–50° W), according to significant canonical correlation between the precipitation field in subtropical South America and the Atlantic Ocean SST anomalies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

Patagonia, located in southern South America, is a vast and remote region holding a rich variety of past environmental records but a small number of meteorological stations. Precipitation over this region is mostly produced by disturbances embedded in the westerly flow and is strongly modified by the austral Andes. Uplift on the windward side leads to hyperhumid conditions along the Pacific coast and the western slope of the Andes; in contrast, downslope subsidence dries the eastern plains leading to arid, highly evaporative conditions. The authors investigate the dependence of Patagonia's local climate (precipitation and near-surface air temperature) year-to-year variability on large-scale circulation anomalies using results from a 30-yr-long high-resolution numerical simulation. Variations of the low-level zonal wind account for a large fraction of the rainfall variability at synoptic and interannual time scales. Zonal wind also controls the amplitude of the air temperature annual cycle by changing the intensity of the seasonally varying temperature advection. The main modes of year-to-year variability of the zonal flow over southern South America are also investigated. Year round there is a dipole between mid- and high latitudes. The node separating wind anomalies of opposite sign migrates through the seasons, leading to a dipole over Patagonia during austral summer and a monopole during winter. Reanalysis data also suggests that westerly flow has mostly decreased over north-central Patagonia during the last four decades, causing a drying trend to the west of the Andes, but a modest increase is exhibited over the southern tip of the continent. [ABSTRACT FROM AUTHOR]

Extreme values of two circulation indices are examined for the time series covering the period 1960-2006. The influence of circulation on surface temperature and rainfall in Argentina is analysed using a zonal index Z and a meridional index R at the 1000 and 500 hPa levels. Seasonal means for all the years representing extreme negative values of R( Z) at 1000 and/or 500 hPa, determine mainly positive (negative) temperature anomalies with increased rainfall in both indices. These characteristics revert for extreme positive values of R( Z). At 1000 hPa, seasonal anomaly trends of R are negative and significant. Trends of Z are all positive and significant, except for winter when they are not significant. Signs of trends at 500 hPa are the same as at 1000 hPa, except for Z in winter and R in summer, whose values are not significant. Annual and seasonal trends of the anomalies of Z differences between 500 and 1000 hPa, are mostly negative, which implies a decrease in baroclinicity in southernmost South America. Analysis of the statistical values obtained for both variables generated by extreme values of R and Z, and of the signs and significance of index trends at 1000 hPa indicates that both circulation indices might contribute to surface temperature warming during the last years of the period 1960/2006. The increase in R, whose influence is greater than that of Z, might contribute to greater rainfall. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Positive trends in annual rainfall in the La Plata Basin (LPB), south of 20°S observed in the last four decades of the twentieth century were not reversed and became more statistically significant when calculated until 2005. These trends were part of a more general change in the monthly precipitation distribution including extreme precipitation. Precipitation in dry and extremely dry months (below the 35th percentile) has been decreasing in the whole LPB region south of 22°S. On the contrary, precipitation in the above normal (between the 65th and 90th percentile) and the extremely high rainfall (above the 90th percentile) ranges has been increasing accounting for most of the annual precipitation trends. More than a steady trend, there has been an abrupt change in extreme monthly precipitation concentrated between 1977 and 1983. The analysis of intensity and frequency of extreme events was done fitting Generalized Extreme Values (GEV) and Poisson distributions. Each distribution was fitted with and without trends in the location parameter and tested to determine the best fit in each case. The regions where GEV with a positive trend was the best fit coincide with areas affected by extensive floods during the last decades. Spatially aggregated results highlight the signal of change towards higher maximum monthly precipitations for a wide span of return periods. The atmospheric circulation associated with cases where extreme monthly precipitation was observed in most of the stations was studied through the integrated water vapour transport in the lower troposphere and its associated divergence. During warm months, an intense northern low-level water vapour flow with two convergence nuclei, one over eastern Argentina, southern Brazil and Uruguay, and the other over western Argentina, along with a weakened south Atlantic Convergence Zone was associated with the more extreme precipitation months favouring the occurrence of Mesoscale Convective Systems. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Global warming affects the hydrological cycle by increasing the frequency and intensity of extreme rainfall events and dry spells. These changes potentially affect the quantity and quality of dissolved organic matter (DOM) input into lakes. In this study, we investigated if changes in precipitation over a 3-year period correspond to changes in DOM and whether these changes affect light attenuation and plankton community composition. We sampled Lake Escondido, a shallow, oligotrophic Andean lake, nine times, analyzing coloured DOM and plankton community composition. During the study period, we observed that variations in the precipitation regime correlated with DOM parameters (water colour and molecular weight), and this, in turn, affected the plankton composition. Chlorophyll a concentrations of both phytoplanktonic fractions (less than and greater than 2 μm) were related to water colour and TDP. We observed in the small fraction (<2 μm) an increase in phycocyanin-rich cells during periods of high water colour. Larger phytoplanktonic cells (>2 μm) presented two biomass peaks corresponding to increases of the cyanophyte Chroococcus planctonicus and of the haptophyte Chrysochromulina parva. As precipitation decreased, the lake became more transparent, favouring C. planctonicus and mixotrophic oligotrich ciliates with endosymbiotic Chlorella. In the context of global climate change, our results highlight the potential impact of changes in precipitation patterns and, consequently, in DOM quality on the plankton community. [ABSTRACT FROM AUTHOR]

Background: In widely distributed species, geographic patterns of phenotypic variation can appear in a clinal (linear or central–marginal) or mosaic fashion in response to environmental factors. Aim: We assessed spatial patterns and possible abiotic drivers of flower and leaf variation in Anarthrophyllum desideratum, an endemic legume found throughout a wide environmental gradient in southern Patagonia. Methods: We measured 10 floral and foliar traits from 26 populations, distributed along the entire range of the species. We examined phenotypic variation within and among populations, geographical patterns, relationships with climatic and edaphic factors and spatial covariation between flowers and leaves, using uni- and multivariate analyses. Results: Most of the studied traits showed higher variability among than within populations. Within-population variability was not associated with population size. Phenotypic differences among populations were structured by geographic distances. Clinal variation patterns, mainly central–marginal, were detected along a south-west to north-east gradient. Flower and leaf size co-varied across populations, whereas, overall phenotypes were weakly coupled. Phenotypic variation was associated with temperature and soil potassium content. Conclusions: Our results support geographically structured patterns of phenotypic variation and suggest that the abiotic environment has an important role in shaping floral and foliar differences among A. desideratum populations. Non-stochastic processes may account for the geographical variation found in this species. [ABSTRACT FROM PUBLISHER]

The article focuses on a research conducted in order to evaluate the influence of weather variables like precipitation and temperature and plant communities on grasshopper density in the Southern Pampas, Argentina. It discusses the effect of increase in summer precipitation on the quantity and quality forage production, affecting these grasshopper populations. The study revealed that weather variables and plant communities had differential influence on the dominant grasshopper species. plant communities on grasshopper density in the Southern Pampas, Argentina. It discusses the effect of increase in summer precipitation on the quantity and quality forage production, affecting these grasshopper populations. The study revealed that

The eastern area of La Pampa Province, Argentina, lies in a transition zone between the humid temperate climate stretching east and the steppe climate stretching west. The area is thus very sensitive to abrupt changes in rainfall. In order to determine the long-term occurrence of such phenomena, long-term annual precipitation series (1921-2004) from 17 stations in the study area were analyzed using the Buishand and Pettitt tests. Results showed a sharp increase in annual rainfall at the southern stations in the 1960s and at the northern and central stations in the 1970s. Increased rainfall can be considered one of the reasons for the subsequent expansion in land planted to crops in the region. While a rapid increase in rainfall can be seen as positive, some researchers believe that if an abrupt decrease in rainfall occurred in future and continued for long, the carrying capacity of the environment could be exceeded, leading to decreased production and environmental degradation. [ABSTRACT FROM AUTHOR]

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This study presents a multitemporal climatology of water excess and shortage during the 20th century in the La Plata Basin. The climatology is based on 0.5 × 0.5 grid across the region. We transform monthly precipitation series for each point into index series at different time scales using the Standardized Precipitation Index (SPI). A month is under water excess (shortage) conditions at different time scales ( i = 6, 9, 12, and 18 months), when SPI[ i]( j) > 1.5 (SPI[ i]( j) < 1.5), where j is the current month. Trends in precipitation were determined using mean regional series of average values over the entire basin. A month when more than 30% of the total basin is under water excesses (shortages) is defined as an excess (shortage) critical month. From the vulnerability point of view, we analyzed the occurrence of critical months. The number of excess critical months increase with time scale of index, and almost all the critical months occurred after 1950 as a consequence of the low-frequency precipitation pattern. That means a noticeable increase in the vulnerability to extended excesses (more than 30% of the area under water excesses) after 1950, especially over the Upper Paraná and the Uruguay basins. For shortage critical months, the behavior depends on time scales. At large time scale (18 and 12 months), almost all the shortage critical months occurred in the period 1901–1950 and only at shorter time scale (9 and 6 months), some critical months appeared after 1950. That means a noteworthy decrease in the basin vulnerability to extended water shortage after 1950 and a moderate decrease in vulnerability to generalized shortage. If we analyze the frequency and mean duration of water excess and shortage events across the basin, we can appreciate that there is a tendency to relate higher frequency regions with regions with lower mean duration events, and conversely. [ABSTRACT FROM AUTHOR]

A weather pattern clustering method is applied and calibrated to Argentinean daily weather stations in order to predict daily precipitation data. The clustering technique is based on k-means and is applied to a set of 17 atmospheric variables from the ERA-40 reanalysis covering the period 1979–1999. The set of atmospheric variables represent the different components of the atmosphere (dynamical, thermal and moisture). Different sensitivity tests are applied to optimize (1) the number of observations (weather patterns) per cluster, (2) the spatial domain size of the weather pattern around the station and (3) the number of members of the ensembles. All the sensitivity tests are compared using the ROC (Relative Operating Characteristic) Skill Score (RSS) derived from the ROC curve used to assess the performance of a predictive system. First, we found the number of observations per cluster to be optimum for values larger than 39. Second, the spatial domain size (~4° × 4°) was found to be closer to a local scale than to a synoptic scale, certainly due to a dominant role of the moisture components in the optimization of the transfer function. Indeed, when reducing the set of variables to the subset of dynamical variables, the predictive skill of the method is significantly reduced, but at the same time the domain size must be increased. A potential improvement of the method may therefore be to consider different domains for dynamical and non-dynamical variables. Third, the number of members per ensembles of simulations was estimated to be always two to three times larger than the mean number of observations per cluster (meaning that at least all the observed weather patterns are selected by one member). The skill of the statistical method to predict daily precipitation is found to be relatively homogeneous all over the country for different thresholds of precipitation. [ABSTRACT FROM AUTHOR]

Statistical models for rainfall downscaling based on multiple linear regression techniques have been developed and tested in the Andean Region of west Argentina, an extended mountainous region where three different rain regimes predominate and rainfall has great spatial and temporal variability. The verification procedure was focused on the model’s ability to reproduce observed rainfall trends in recent decades. In the northwest of Argentina, domain of the tropical summer rain regime, the monthly rainfall variance accounted for by downscaling models was 77% on average and models reproduced satisfactorily the negative linear trend observed in the last two decades of the past century. In the arid central-west Argentina, a region of rapid transition between two different rain regimes, model performance was rather poor (an average of 50% of explained variance), even so models were able to capture outstanding differences in the linear trend between the northern and southern sectors of the region. In the southwest of Argentina, domain of the mid-latitude winter rain regime, the monthly variance accounted for by downscaling models was 71% on average and models were capable to reproduce a singular change in the onset of the rainy season that occurred during the 1990s. The results achieved demonstrate that it is feasible to establish significant and useful statistical relationships between atmospheric variables and rainfall at monthly and river basin scales, even for a topographically complex region like western Argentina. [ABSTRACT FROM AUTHOR]

Anthropogenic habitat disturbance can have profound effects on multiple components of forest biotas including pollinator assemblages. We assessed the effect of small-scale disturbance on local richness, abundance, diversity and evenness of insect pollinator fauna; and how habitat disturbance affected species turnover across the landscape and overall diversity along a precipitation gradient in NW Patagonia (Argentina). We evaluated the effect of disturbance on overall pollinator fauna and then separately for bees (i.e. Apoidea) and non-bee pollinators. Locally, disturbed habitats had significantly higher pollinator species richness and abundances than undisturbed habitats for the whole pollinator assemblage, but not for bees or non-bees separately. However, significant differences in species richness between habitats vanished after accounting for differences in abundance between habitat types. At a local scale Shannon-Weaver diversity and evenness did not vary with disturbance. A β diversity index indicated that, across forest types, species turnover was lower between disturbed habitats than between undisturbed habitats. In addition, rarefaction curves showed that disturbed habitats as a whole accumulated fewer species than undisturbed habitats at equivalent sample sizes. We concluded that small patches of disturbed habitat have a negligible effect on local pollinator diversity; however, habitat disturbance reduced β diversity through a homogenization of the pollinator fauna (in particular of bees) across the landscape. [ABSTRACT FROM AUTHOR]

We did a brief description of the climatic behavior and after this we analyzed the temporal variation in the total number of days a year with rainfall and the number of days a year with rainfall above the 100 mm threshold at the rain gauging stations in northeastern Argentina south of the La Plata River basin. The results show an increase both in the frequency of daily rainfall, especially during the winter season, and the frequency of days with heavy rainfall starting in the early 1970s. The increase in frequency of occurrence is more significant in the case of heavy rainfall. The annual maximum rainfall was calculated for periods of 1, 3, 5, 7, and 10 consecutive days at regional rain gauging stations for the respective historical periods, and the rain intensity–duration–return period curves (IDT) were determined on a frequency analysis. The IDT curves were compared with rainfall intensity–duration data of critical storms occurring in the last decades. We noticed that the rain intensities of critical storms (mostly convective) widely exceeded the intensities given by the 100-year IDT curves, particularly for short durations. The increase in both the frequency of heavy rainfall occurrence and rain intensity from the 1970s onward shows an increase in frequency and intensity of the meso-scale convective systems in the region resulting from climatic change. These systems tend to produce rainfall of very high intensity that is spatially concentrated and which generally produces significant floods in the local rivers. [ABSTRACT FROM AUTHOR]

Summer rainfall variability (October to March) shows inter-annual to multi-decadal fluctuations over a vast area of subtropical Argentina between 28°S–38°S and 65°W–70°W. Statistically significant oscillations of quasi-period in the bands of 18–21, 6, 4 and 2 years can be found throughout the region and intra-regionally, though the latter are variable. The lower frequency variation produces alternating episodes of above and below normal rainfall each lasting roughly 9 years. This quasi-fluctuation appears to be shared with the summer rainfall region of South Africa and were in-phase related one another until mid-1970s. The teleconnection between both subtropical regions could be generated by an atmospheric-oceanic bridge through the global sea surface temperatures (SSTs), particularly those of the equatorial-tropical South Atlantic. From mid-1970s, the alternating wet and dry pattern has been interrupted in the Argentine region producing the longest, as yet unfinished, wet spell of the century. Thus, a significant change of the long-term variation was observed around 1977 toward lower frequencies. Since then the statistical model that explains more than 89% of the variance of the series until 1977, diverges from the observed values in the 1980s and 1990s. In addition the Yamamoto statistical index, employed to detect a climatic jump, reaches its major value in 1973 at the beginning of the current long wet spell. Therefore the change could be located between 1973 and 1977. Application of the t-student's test gives significant differences of mean values for pre-1977 and post-1977 sub-samples from both individual time series and the regional index series. The spectral analysis also shows changes in energy bands in concordance with the features of the change that occurred from mid-1970s. The change gives rise to a significant increment of more than 20% in average of normal rainfall over the region. Conversely, a drought between mid-1980s and the 1990s has been observed in the South African counterpart with severe characteristics, thereby continuing the quasi-18-year oscillation. Consequently, the low-frequency coherent behaviour between both the Argentine and South African regions is lost from the mid-1970s. The analysis of association of wet/dry spells and warm/cold, El Niño/La Niña episodes appears to be not significant at scales of year-to-year variability although at decadal to multi-decadal scales the association could be relevant. More than one process of multi-decadal variability of global SSTs could influence the Argentine summer rainfall region and the former bi-decadal teleconnection. Finally, potential hypothetical factors of change are discussed, such as the strengthening of direct and indirect mechanisms of moisture flux transport associated with global warming, low-level atmospheric circulation changes and/or to SSTs mean condition long-term variations over tropical and subtropical South Atlantic and South Pacific oceans. [ABSTRACT FROM AUTHOR]