Silvina A. Solman

Regional Climate Modeling over South America: A Review

This review summarizes the progress achieved on regional climate modeling activities over South America since the early efforts at the beginning of the 2000s until now. During the last 10 years, simulations with regional climate models (RCMs) have been performed for several purposes over the region. Early efforts were mainly focused on sensitivity studies to both physical mechanisms and technical aspects of RCMs. The last developments were focused mainly on providing high-resolution information on regional climate change. This paper describes the most outstanding contributions from the isolated efforts to the ongoing coordinated RCM activities in the framework of the CORDEX initiative, which represents a major endeavor to produce ensemble climate change projections at regional scales and allows exploring the associated range of uncertainties. The remaining challenges in modeling South American climate features are also discussed.

Regional climate simulations over South America: sensitivity to model physics and to the treatment of lateral boundary conditions using the MM5 model

In this study the capability of the MM5 model in simulating the main mode of intraseasonal variability during the warm season over South America is evaluated through a series of sensitivity experiments. Several 3-month simulations nested into ERA40 reanalysis were carried out using different cumulus schemes and planetary boundary layer schemes in an attempt to define the optimal combination of physical parameterizations for simulating alternating wet and dry conditions over La Plata Basin (LPB) and the South Atlantic Convergence Zone regions, respectively. The results were compared with different observational datasets and model evaluation was performed taking into account the spatial distribution of monthly precipitation and daily statistics of precipitation over the target regions. Though every experiment was able to capture the contrasting behavior of the precipitation during the simulated period, precipitation was largely underestimated particularly over the LPB region, mainly due to a misrepresentation in the moisture flux convergence. Experiments using grid nudging of the winds above the planetary boundary layer showed a better performance compared with those in which no constrains were imposed to the regional circulation within the model domain. Overall, no single experiment was found to perform the best over the entire domain and during the two contrasting months. The experiment that outperforms depends on the area of interest, being the simulation using the Grell (Kain–Fritsch) cumulus scheme in combination with the MRF planetary boundary layer scheme more adequate for subtropical (tropical) latitudes. The ensemble of the sensitivity experiments showed a better performance compared with any individual experiment.

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.

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 Change Scenario for Central Argentina: A Statistical Downscaling Approach

With the purpose of assessing the vulnerability of crop production in Argentina related to the impact of global warming, we estimated local changes of monthly mean precipitation for summer and winter months caused by CO2 doubling, at selected stations lying in central Argentina. A statistical downscaling approach was developed by means of empirical relationships between large-scale climatic variables from the NCEP re-analyses data set and local scale precipitation data. The method was tested against an independent set of observed data and subsequently applied to the Max Plank Institute (MPI) GCM control run. Despite the simplicity of the statistical approach developed, it was able to satisfactorily reproduce the spatial patterns of the regional precipitation field. The response of the climate system to the enhanced emission scenario simulated by the MPI model was used to infer the local climate change. A precipitation decrease over the region of interest is simulated by the MPI model for the increased CO2 scenario. Accordingly, with the GCM potential changes, the local precipitation decrease is higher in summer than in winter. This result has an important consequence for the rainfall regime over the region, namely that a higher decrease of rainfall is projected for the rainy season while a weaker decrease is projected for the dry season. Regional scenarios of climate change, including both rainfall and extreme temperatures were then used to assess the impact of climate change on crops (wheat, maize, sunflower and soybean) and pastures production in the Pampas region in order to evaluate the vulnerability of the system to global warming.

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.