Mario Bidegain

Trends in Total and Extreme South American Rainfall in 1960–2000 and Links with Sea Surface Temperature

A weeklong workshop in Brazil in August 2004 provided the opportunity for 28 scientists from southern South America to examine daily rainfall observations to determine changes in both total and extreme rainfall. Twelve annual indices of daily rainfall were calculated over the period 1960 to 2000, examining changes to both the entire distribution as well as the extremes. Maps of trends in the 12 rainfall indices showed large regions of coherent change, with many stations showing statistically significant changes in some of the indices. The pattern of trends for the extremes was generally the same as that for total annual rainfall, with a change to wetter conditions in Ecuador and northern Peru and the region of southern Brazil, Paraguay, Uruguay, and northern and central Argentina. A decrease was observed in southern Peru and southern Chile, with the latter showing significant decreases in many indices. A canonical correlation analysis between each of the indices and sea surface temperatures (SSTs) revealed two large-scale patterns that have contributed to the observed trends in the rainfall indices. A coupled pattern with ENSO-like SST loadings and rainfall loadings showing similarities with the pattern of the observed trend reveals that the change to a generally more negative Southern Oscillation index (SOI) has had an important effect on regional rainfall trends. A significant decrease in many of the rainfall indices at several stations in southern Chile and Argentina can be explained by a canonical pattern reflecting a weakening of the continental trough leading to a southward shift in storm tracks. This latter signal is a change that has been seen at similar latitudes in other parts of the Southern Hemisphere. A similar analysis was carried out for eastern Brazil using gridded indices calculated from 354 stations from the Global Historical Climatology Network (GHCN) database. The observed trend toward wetter conditions in the southwest and drier conditions in the northeast could again be explained by changes in ENSO.

Observed Trends in Indices of Daily Temperature Extremes in South America 1960–2000

Abstract A workshop on enhancing climate change indices in South America was held in Maceio, Brazil, in August 2004. Scientists from eight southern countries brought daily climatological data from their region for a meticulous assessment of data quality and homogeneity, and for the preparation of climate change indices that can be used for analyses of changes in climate extremes. This study presents an examination of the trends over 1960–2000 in the indices of daily temperature extremes. The results indicate no consistent changes in the indices based on daily maximum temperature while significant trends were found in the indices based on daily minimum temperature. Significant increasing trends in the percentage of warm nights and decreasing trends in the percentage of cold nights were observed at many stations. It seems that this warming is mostly due to more warm nights and fewer cold nights during the summer (December–February) and fall (March–May). The stations with significant trends appear to be loca...

An Observed Trend in Central South American Precipitation

Abstract Seasonal linear trends of precipitation from South American station data, which have been averaged onto grids, are examined, with emphasis on the central continent. In the period 1976–99, the largest trend south of 20°S occurs during the January–March season, is positive, and is centered over southern Brazil. From 1948 to 1975 the trend is also positive, but with less than half the slope. The trend is not due to a systematic change in the timing of the rainy season, which almost always starts before January and usually ends after March, but rather results from an increase in the percent of rainy days, and an increase in the rainy day average. The dynamic causes of the trend are not obvious. It does not appear to be accounted for by an increase in synoptic wave activity in the region. The precipitation trend is related to a positive sea surface temperature trend in the nearby Atlantic Ocean, but apparently not causally. The trend in the Atlantic seems to result from a decrease in mechanical stirri...

A Stochastic Precipitation Generator Conditioned on ENSO Phase: A Case Study in Southeastern South America

Abstract Stochastic precipitation generators can produce synthetic daily rainfall series with statistical characteristics similar to those of historical data. Typically, parameters of precipitation generators have been fit using all historical data for a given period. This approach, however, fails to capture differences in the precipitation process associated with an El Nino–Southern Oscillation (ENSO) signal. Stochastic precipitation generators conditioned on the ENSO phase were developed to address this problem. Precipitation models with a range of parameterization schemes were tested in six locations in central-eastern Argentina and western Uruguay (southeastern South America), an important agricultural region with a clear ENSO precipitation signal in October–March. Conditional precipitation models (occurrence, intensity, or both) were superior to simple models in 24 of the 36 locations/months analyzed. Graphic diagnostics showed that conditional occurrence models successfully captured differences in t...

Integrating Climate Science, Monitoring, and Management in the Rio de la Plata Estuarine Front (Uruguay)

The study presents an institutional arrangement for managing some risks associated with hydroclimatic variability in the Rio de la Plata River Estuarine Frontal System (EFS). The goals are to contribute to an efficient coordination work between local agencies that manage the use of ecosystem services, and to incorporate climate science and management options in coastal areas of Uruguay. We have identified and analysed climate forcing ENSO and the variables river flow and winds, which govern the location and displacement of the frontal system, where the capital city Montevideo is located, and the fluctuations of salinity. The study analyses the austral spring–summer period (October–March) from 1997/1998 to 2012/2013. Fish catch and beach quality were selected as examples of environmental impacts of climate forcing which are presented as a causality loop diagram (CLD): ENSO → (River flow, wind, rainfall) → (EFS displacement, Salinity), and state/impact indicators → (Fish catch, Beach quality). Institutional cooperation has been developed to incorporate climate adaptation regarding the Frontal System. GEF Project “Implementing Pilot Adaptation Measures to Climate Change in coastal areas of Uruguay”, in which the Directorate of the Environment, the University of the Republic, and the Government of Montevideo collaborate on improving climate science, monitoring, and management in the fields of Estuarine and Environmental Management has provided the framework for the present study.