Magnitude and frequency of heat and cold waves in recent decades: the case of South America

Abstract

Abstract. In recent decades there has been an increase in magnitude and occurrence of heat waves and a decrease of cold waves which are possibly related to the anthropogenic influence (Solomon et al., 2007). This study describes the extreme temperature regime of heat waves and cold waves across South America over recent years (1980–2014). Temperature records come from the Global Surface Summary of the Day (GSOD), a climatological dataset produced by the National Climatic Data Center that provides records of daily maximum and minimum temperatures acquired worldwide. The magnitude of heat waves and cold waves for each GSOD station are quantified on annual basis by means of the Heat Wave Magnitude Index (Russo et al., 2014) and the Cold Wave Magnitude Index (CWMI, Forzieri et al., 2015). Results indicate an increase in intensity and in frequency of heat waves, with up to 75 % more events occurring only in the last 10 years. Conversely, no significant changes are detected for cold waves. In addition, the trend of the annual temperature range (i.e., yearly mean of Tmax – yearly mean of Tmin) is positive – up to 1 °C decade−1 – over the extra-tropics and negative – up to 0.5 °C decade−1 – over the tropic. This dichotomous behaviour indicates that the annual mean of Tmax is generally increasing more than the annual mean of Tmin in the extra-tropics and vice versa in the tropics.