Mario N. Nuñez

The salinity front of the Río de la Plata ‐ A numerical case study for winter and summer conditions

A 3-D baroclinic model has been applied to investigate the location of the salinity front of the Rio de la Plata. River run-off, tides and mean winds for summer and winter conditions respectively were considered in order to find out the most important factors for the observed seasonal variability of this location. The results show that wind forcing is responsible for the observed variability in summer. In winter, wind forcing is not important, but the river discharge. The resulting surface salinity distributions show a surprisingly good agreement with the present knowledge from observations.

A Set of 3-D Nested Models for Tidal Propagation from the Argentinean Continental Shelf to the Río de la Plata Estuary—Part I. M2

Abstract As a contribution to the UNDP/GEF project ‘Environmental Protection of the Río de la Plata and its Maritime Front’, the three-dimensional primitive equation Hamburg Shelf Ocean Model is being implemented for forecasting purposes. As a first step a study of the tidal propagation was done. Data for the estuary were gained through a set of three one-way nested models. Simulations were started with a large-scale model covering the Argentinean and Uruguayan and part of the Brazilian continental shelves. This model provides boundary conditions to a smaller scale model of the Río de la Plata and adjacent continental shelf, which in turn is used to force a small-scale high-resolution model of the Río de la Plata estuary. Model sensitivity to different boundary conditions and to model parameters was investigated. Solutions are not sensitive to the two different boundary conditions tested, derived from global data assimilating models. It results also not sensitive to lateral diffusion but to bottom friction. M2 tidal wave propagates northwards as a Kelvin wave, with amplitudes reaching almost 4 m in Southern Patagonia and a few centimeters at the Río de la Plata estuary. Simulation results for the M2 component propagation were validated using all tidal gauge data available and several currents observations, resulting in a very good agreement. These simulations have permitted, therefore, the construction of more reliable model derived cotidal, corange and tidal currents charts. The nonlinear transfer of energy from semidiurnal to higher order harmonics was mapped. It can reach very high values at some locations of the Patagonian coast. Tidal energy dissipation derived from the simulations shows that it constitutes an important amount of the globally estimated one.

Climate change scenarios over the South American region: an intercomparison of coupled general atmosphere-ocean circulation models

Results of four different coupled atmosphere-ocean general circulation model runs for South America and surrounding oceans are examined. The mean response of the simulated climate system to a gradual increase of greenhouse gases is presented. The transient coupled experiment data provided for the Intergovernmental Panel on Climate Change (IPCC) were the most recent available to us at the time of this study, from the following research centres in Europe and USA: the UK Meteorological Office (UKMO), the Max-Planck Institute for Meteorology (MPI), the Geophysical Fluid Dynamic Laboratory (GFDL) and the National Center for Atmospheric Research (NCAR). The regional performance of the control simulations (with fixed CO2 concentration) is determined by comparing sealevel pressure, near-surface zonal wind, precipitation and surface air temperature from the models, against observed climatological fields. The response of the climate system to the enhanced emission scenarios is established comparing the control experiments with the respective transient experiments around the time of doubling CO2. To assist in estimating likely future climate change in the South American region, only the results of those model experiments with the best control simulation of current climate in the region are considered: the UKMO and MPI models. A maximum warming over the continent and a minimum warming in the extratropical oceans, a slight intensification and southward migration of the subtropical ridge, a deepening of the sub-Antarctic trough, an intensification of the westerly winds, and increasing precipitation in the tropics and in the mid-latitude oceans are the most important potential changes simulated by both models for the increased CO2 scenarios. # 1997 Royal Meteorological Society. Int. J. Climatol., Vol. 17, 1613‐1633

Climate change and wheat production in Argentina

The aim of this work is to assess the impact of past and future climate changes on wheat productivity in the Pampas region of Argentina. The study was based on long-term climatic and crop productivity data, regional climatic scenarios and a crop simulation model. Our results demonstrate that the potential wheat yield has been declining at increasing rates since 1930 mainly due to minimum temperature increases. Further increases in temperature could lead to potential wheat yield reductions of 7.5% for each °C of temperature rise. If the expected effects of CO2 really do occur, the decline of the potential wheat yields due to temperatures that are 2.5°C warmer could be entirely offset by a CO2 concentration of 550 ppm. If the CO2 effects are not considered, rainfed wheat yields could be reduced by 4% by the end of the 21st century (2080), the northern part of the Pampas region being the most affected zone. Inversely, if the CO2 effects are considered, rainfed wheat yield could increase by 14%. Advancing planting dates could be a good strategy to take advantage of new environmental conditions with prolonged frost-free periods.

Relationship between ENSO cycles and frost events within the Pampa Húmeda region

The objective of the present paper is to analyse the possible impact of ENSO events on the spatial and the temporal distribution of frost occurrences, within the central region of Argentina. Therefore, the minimum temperature series have been studied for 41 meteorological stations within the Pampa Humeda region and, for a period of 30 years from 1961 to 1990, exploring possible relationships with El Nino (EN)/La Nina (LN) events and the changes in the Southern Oscillation. It can be concluded that part of the frost frequency variability within this region is explained by the ENSO cycle. Results indicate that, for at least 1 of the 2 years in which the EN event takes place, the mean number of frost occurrences drops below the climatological value. The low phase of the Southern Oscillation Index (SOI) also coincides with those years for which the number of frost events remained below the total annual mean in all cases, with the year 1965 as an exception. Conversely, during the high phase of the SOI, this number was above the total annual mean for four of the six classified cases. In the particular case of seasonal frost occurrence, it is related to the warm event development state, exhibiting a greater impact during the autumn and winter months, for which the cold event also seems to have influence. Copyright

Climate change impacts on regional maize yields and possible adaptation measures in Argentina

In this work, the impact of future climate (2081-2090) on regional maize yields was assessed through a crop simulation model. The climatic inputs correspond to the regional model MM5/CIMA, considering grids of 50 km * 50 km. Crop model runs were done under typical crop management conditions with and without considering the fertilisation effect of CO2. Without CO2 effects, the impact of future scenarios will be negative in most of the region, attaining mean reductions of 9% and 6% under SRES A2 and B2, respectively. However, yield changes could range between increases of 46% under B2 and decreases of 17% under A2. The inclusion of CO2 effects led to increases in maize yields by 19% under A2 and 11% under B2, although negative impacts could still occur. The adaptation measures related to planting dates and irrigation were assessed as a way to overcome future negative impacts. Without considering CO2, advancing sowings by 15-30 days could be beneficial, increasing yields under B2 and reducing loses under A2. Irrigation requirements could, on average, increase in the central and northern parts of the region and decrease in the southern one. The uncertainties related to future scenarios and the crop responses to CO2 are also discussed.

Regional climate change scenarios over southern South America for future climate (2080-2099) using the MM5 Model. Mean, interannual variability and uncertainties

Fil: Cabre, Maria Fernanda. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmosfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmosfera; Argentina. Centre National de la Recherche Scientifique; Francia

Assessment of a Regional Climate for South America: A Dynamical Downscaling Approach

The current coarse resolution of general circulation models (GCMs) does not provide reliable estimates of precipitation and other variables at the appropriate scales required for regional climate studies over the South American region. To overcome this problem, one possibility is to perform regional climate simulations using limited-area models nested in global models. A research effort aimed at the development of this downscaling technique for the region extending from the South Pacific across South America to the western South Atlantic is now under way at the Centro de Investigaciones del Mar y la Atmosfera (CIMA), Buenos Aires. The technique consists of using the output of GCM simulations to provide initial driving conditions and time-dependent lateral boundary conditions for regional climate model (RCM) simulations over South America and the adjacent oceans (one way nesting). The singularity of this nesting system is that the global model itself has a stretched, variable horizontal resolution, with the grid irregularly spaced in the meridional direction. This stretched grid is introduced in order to improve resolution in a latitudinal band over the region of interest. Hence, we use a “hybrid” strategy in which a regional model is nested in a global variable-resolution model, combining traditional nesting with GCM zooming, at a relatively low computational cost. This pilot study introduces an initial diagnosis of the capabilities of the RCM for simulating climate in the South American region. Our preliminary results suggest that the nesting technique is a computationally low-cost alternative suitable for simulating regional climate features. However, before applying this nesting system to problems involving the local response to climate change, additional simulations, tuning of parameters and further diagnosis are clearly needed to represent regional patterns more precisely.