Trends and Decadal Variability in Air Temperature over Southern Brazil

This study presents an investigation on the decadal variability of maximum (Tmax) and minimum (Tmin) air temperature in southern Brazil during the period 1961-2011. Daily data from 26 meteorological stations, obtained from Brazil's National Meteorology Institute (INMET), were used to calculate annual and decadal means and standard deviations. From the annual statistics we computed linear trends in Tmin, Tmax and daily temperature range (DTR). The decadal means were used to compute changes in Tmax and Tmin. Annual anomalies were obtained by removing the climatology for 1961-2011. Results show that most of the region experienced a statistically significant increase in both Tmin and Tmax, i.e. nights as well as days are becoming hotter. The increase in Tmin is however more pronounced than in Tmax, resulting in a decrease in DTR. Of particular notice were the increases in Tmin over the state of Parana and in Tmax along the southern Brazilian coast. Trends in standard deviations show asignificant increase in the amplitude of variability of Tmin for most of the region's stations. Overall, there was a cooling period during the 1960s and 70s. From the early 1980s until early 90s we observed a sharp and unprecedented warming in both Tmin and Tmax time series. After 1993 the Tmax and Tmin anomalies are relatively smaller in magnitude and, in the last eight years of the record, temperatures remained near the climatological average. These results suggest a halt in the overallwarming trend over southern Brazil after mid-2003. Since the 18th century's Industrial Revolution and the increasing use of fossil fuels, we have observed a steady increase in the concentration of greenhouse gases and aerosols in the atmosphere. In 2011, the concentration of carbon dioxide, methane, and nitrous oxide had surpassed pre-industrial levels by 40%, 150%, and 20%, respectively. Changes in land use such as deforestation and urbanization, concomitant with the warming atmosphere, have been affecting the global climate and its natural variability. The changes we observe in the climate are therefore a combination of anthropogenic and natural forcing effects (7). Hundreds of studies report significant changes in climate all over the planet (5-7), acknowledging an ongoing global climate change in which the elements air temperature and precipitation appear to be the most affected ones (14). These changes have very diverse regional manifestations, with varying magnitudes and spatial distributions in precipitation patterns, temperature changes, sea level rise, etc. (13). Changes in air temperature are responsible for