The Drought of Amazonia in 2005

TLDR

Large sections of southwestern Amazonia experienced one of the most intense droughts of the last century, and the choice of rainfall data influenced its detection. The drought was driven by a warm tropical North Atlantic, reduced northeast trade‑wind moisture transport into southern Amazonia during peak summer, and weakened upward motion that suppressed convective development and rainfall. The event severely impacted human populations along the Amazon River and its western tributaries, caused historic low river levels that halted navigation, was absent from central and eastern Amazonia unlike past El Niño droughts, intensified in September with lower humidity and higher temperatures, sparked forest fires, and was followed by rains in October and flooding after February 2006, with most rainfall datasets indicating deficits except one showing above‑normal precipitation.

Abstract

Abstract In 2005, large sections of southwestern Amazonia experienced one of the most intense droughts of the last hundred years. The drought severely affected human population along the main channel of the Amazon River and its western and southwestern tributaries, the Solimões (also known as the Amazon River in the other Amazon countries) and the Madeira Rivers, respectively. The river levels fell to historic low levels and navigation along these rivers had to be suspended. The drought did not affect central or eastern Amazonia, a pattern different from the El Niño–related droughts in 1926, 1983, and 1998. The choice of rainfall data used influenced the detection of the drought. While most datasets (station or gridded data) showed negative departures from mean rainfall, one dataset exhibited above-normal rainfall in western Amazonia. The causes of the drought were not related to El Niño but to (i) the anomalously warm tropical North Atlantic, (ii) the reduced intensity in northeast trade wind moisture transport into southern Amazonia during the peak summertime season, and (iii) the weakened upward motion over this section of Amazonia, resulting in reduced convective development and rainfall. The drought conditions were intensified during the dry season into September 2005 when humidity was lower than normal and air temperatures were 3°–5°C warmer than normal. Because of the extended dry season in the region, forest fires affected part of southwestern Amazonia. Rains returned in October 2005 and generated flooding after February 2006.