Abstract
Abstract. In this study, we assess how the anthropogenically induced increase in greenhouse gas concentrations affects the climate of central and southern South America. We utilise two regional climate simulations for present day (PD) and pre-industrial (PI) times. These simulations are compared to historical reconstructions in order to investigate the driving processes responsible for climatic changes between the different periods. The regional climate model is validated against observations for both re-analysis data and GCM-driven regional simulations for the second half of the 20th century. Model biases are also taken into account for the interpretation of the model results. The added value of the regional simulation over global-scale modelling relates to a better representation of hydrological processes that are particularly evident in the proximity of the Andes Mountains. Climatic differences between the simulated PD minus PI period agree qualitatively well with proxy-based temperature reconstructions, albeit the regional model overestimates the amplitude of the temperature increase. For precipitation the most important changes between the PD and PI simulation relate to a dipole pattern along the Andes Mountains with increased precipitation over the southern parts and reduced precipitation over the central parts. Here only a few regions show robust similarity with studies based on empirical evidence. However, from a dynamical point-of-view, atmospheric circulation changes related to an increase in high-latitude zonal wind speed simulated by the regional climate model are consistent with numerical modelling studies addressing changes in greenhouse gas concentrations. Our results indicate that besides the direct effect of greenhouse gas changes, large-scale changes in atmospheric circulation and sea surface temperatures also exert an influence on temperature and precipitation changes in southern South America. These combined changes in turn affect the relationship between climate and atmospheric circulation between PD and PI times and should be considered for the statistical reconstruction of climate indices calibrated within present-day climate data.
Highlights
The climate of South America is influenced by the interplay of different large-scale atmospheric and oceanic phenomena and topographic features of the continent
The model bias induced by the driving ECHO-G model has to be considered, i.e., the overestimation in the high-latitude zonal circulation in the present-day simulation compared to re-analysis data
Two simulations with the regional climate model CCLM have been investigated for climatic changes between present-day and pre-industrial times
Summary
The climate of South America is influenced by the interplay of different large-scale atmospheric and oceanic phenomena and topographic features of the continent. The authors conclude that the REMO refor the Andes Mountains Neglecting this effect would po- gional model improves the global reanalysis data tentially lead to a false interpretation of results obtained by for temperature in the tropical regions during the warm seathe climate model simulation. This point was emphasised by son and for precipitation in the subtropics and extratropical Solman et al (2008), stating that differences in mountainous regions. This point was emphasised by son and for precipitation in the subtropics and extratropical Solman et al (2008), stating that differences in mountainous regions. regions between their MM5 simulations and other gridded www.clim-past.net/8/1599/2012/
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