Surface air temperature trends in Southern Brazil for 1960-2002

Trends in minimum and maximum air temperature and in the diurnal thermal range (DTR), and derived indices of extreme temperatures since the 1960's are assessed for southern Brazil. Most meteorological stations show steep increases in the night-time temperatures (depicted by the minimum temperature) as compared to slight increases in the daytime temperature (depicted by the maximum temperature), both year round and at the seasonal level. The warming trends are stronger during winter as compared to summer. Consequently, the observed annual and seasonal negative DTR trends in southern Brazil during the last 40 years are largely due to the greater increase in nighttime temperatures rather than daytime temperatures. At decadal timescales, the presence of more intense and frequent El Nino events during the last 20 years also contributes to warming and explains the steep increase in the air temperature extremes trends during this period, as compared to the relatively colder 1960-1980 period, especially for winter. Indices of temperature extremes defined using fixed limits for maximum and minimum temperatures for colder or warmer days were compared with percentile-based indices defined in the recent literature. The comparison shows that the frequency of warmer days increased during both summer and winter, especially during the last two decades. The observed positive tendencies in minimum temperatures and warmer days during winter occur even though extreme cold events and freezing conditions occurred in 1975, 1994 and 2000. Copyright (C) 2007 Royal Meteorological Society.