The heat wave of October 2020 in central South America

Abstract During September–November 2020, the meteorological services of Brazil, Argentina, Peru, Paraguay, and Bolivia reported record‐high maximum temperatures in several warm spells during this season. Positive and significant trends in heat wave frequency, intensity, and duration have been recorded since the 1980s, particularly in large cities. In this study, a heat wave is defined as a period in which both daily maximum and minimum air temperatures exceed the corresponding climatological 90th percentile for three or more consecutive days during September–November 2020. In this period, an intense heat wave during the first half of October and two heat waves events in November resulted in record‐breaking daily maximum temperatures in several locations in central South America. Places experienced temperature of about 10°C above normal, and some locations reported maximum temperatures above 40°C for several days in a row. Because its intensity and geographical extension, affecting central South America from southern Peruvian Amazon to southeastern Brazil, the heat wave of September 23–October 15 was selected as a case study. This intense heat wave was due a persistent atmospheric blocking located starting in late September and lasting until middle October 2020, a continuous presence of a warm air mass for several consecutive days contributed to pronounced positive temperature anomalies, possibly reinforced by extremely low soil moisture. This makes it easier for these high‐pressure systems to generate extreme heat waves because more of the sun's energy is going into heating the atmosphere rather than evaporating non‐existent water in the soil. This heat wave aggravated the drought over the Pantanal and other regions in October 2020, increasing fires and impacts on natural and human systems, representing a severe drought‐heat compound event. This vicious cycle of drought and extreme heat is of the kind expected under a warming climate.