Hydro-climatic and ecological behaviour of the drought of Amazonia in 2005IntroductionData and methodologyResults and discussionsClimatic features of the drought of 2005Hydrological features of the droughtNear-surface climate conditions and fire risk during the drought of 2005Discussions and conclusionsWe are thankful for funding from the Brazilian Research Council CNPq, the Probio project (Projeto de Conservação e Utilização Sustentável da Diversidade Biológica Brasileira) from the MMA/BIRD/GEF/CNPq, the project Using Regional Climate Change Scenari...ReferencesHydro-climatic and ecological behaviour of thedrought of Amazonia in 2005J. A. Marengo1,*, C. A. Nobre1, J. Tomasella1, M. F. Cardoso1and M. D. Oyama21CPTEC/INPE, Rodovia Presidente Dutra, 12630-000 Cachoeira Paulista, Sa˜o Paulo, Brazil2Divisa˜odeCieˆncias Atmosfe´ricas, Centro Te´cnico Aeroespacial (CTA), Instituto de Aerona´utica e Espac¸o (IEA ),Prac¸a Marechal Eduardo Gomes, 50, 12228-904 Sa˜o Jose dos Campos, Sa˜o Paulo, BrazilIn 2005, southwestern Amazonia experienced the effects of an intense drought that affected life andbiodiversity. Several major tributaries as well as parts of the main river itself contained only a fraction oftheir normal volumes of water, and lakes were drying up. The consequences for local people, animals andthe forest itself are impossible to estimate now, but they are likely to be serious. The analyses indicate thatthe drought was manifested as weak peak river season during autumn to winter as a consequence of aweak summertime season in southwestern Amazonia; the winter season was also accompanied by rainfallthat sometimes reached 25% of the climatic value, being anomalously warm and dry and helping in thepropagation of fires. Analyses of climatic and hydrological records in Amazonia suggest a broadconsensus that the 2005 drought was linked not to El Nin˜oaswithmostpreviousdroughtsintheAmazon, but to warming sea surface temperatures in the tropical North Atlantic Ocean.Keywords: Amazon; drought; climate change1. INTRODUCTIONDrought, fire and their interactions play an importantrole in the carbon dynamics, vegetation–atmosphereinteractions, hydrology and health of Amazon forestecosystems, and in the livelihoods of Amazon residents.In a normal year, the region receives over 2500 mm/yearrainfall. Yet, from November 2004 to the end of 2005,this region was affected by an increasingly catastrophicdrought, estimated to be the worst in 40 years (Marengoet al.2008).Previous drought events occurred during El Nin˜oyears(e.g. 1926, 1983 and 1998), while the previous droughtthat was unrelated to El Nin˜o was in 1964. MostAmazonian droughts during El Nin˜ooccurredinthenortheastern Amazon, but the one in 2005 started in thewest and southwest, and its impact spread as far asthe centre and east. In 2005, from Peru to Eastern Brazil,the effects of the drought were dramatic —several majortributaries as well as parts of the main river itself containedonly a fraction of their normal volumes of water, and lakeswere drying up. The consequences for local people,animals and the forest itself were serious.In a region with few roads, no river transport means noincoming supplies, and also leaves local farmers unable tosell their crops. River floodplains dried up—people couldthenwalk and cycle in placeswhere previously canoes andriverboats were the only means of transport. Inevitably,fishes died in millions—their bodies clogged the rivers,poisoning the water and making it impossible for localpeople to drink. Towns were lacking food, medicines andfuel because boats could not get through.The causes of the drought were not related to El Nin˜obut to (i) an anomalously warm tropical North Atlantic,(ii) a reduced intensity in northeast trade wind moisturetransport into southern Amazonia during the peaksummertime season, and (iii) a weakened upward motionover this section of Amazonia, resulting in reducedconvective development and rainfall. The droughtconditions were intensified during the dry season untilSeptember 2005 when humidity was lower than normaland air temperatures 3–58C warmer than normal. At thistime, the river levels were well below normal andnavigation was not possible in many parts of the Solimo˜esRiver. Rains returned in October 2005 and generatedflooding after February 2006 (Marengo et al. 2008).To make matters worse, as the rainforest becameincreasingly dry, damaging wildfires regularly broke outacross the region, destroying thousands of hectares oftrees. Owing to the extended dry season in the region,forest fires affected a part of southwestern Amazonia.The fires occurred mainly where there was humanactivity, which could ignite them. In the Brazilian Stateof Acre, in southwestern Amazonia, CPTEC/INPE(www.cptec.inpe.br/queimadas) has reported that thenumber of fire pixels detected using the NOAA12satellite tripled to nearly 2800 at its peak in September2005, compared with 800 in 2004. In Amazonas, thenumber of fire pixels in September 2004 was 760 whilein September 2005 it nearly tripled to 2166. Amazoniandeforestation and fires account for more than 75% ofBrazil’s greenhouse gas emissions and place it among thetop four contributors to global climate change.Reviews on the spatial extent of the droughts and fireresponse to the 2005 drought are found in Brown et al.Phil. Trans. R. Soc. B (2008) 363, 1773–1778doi:10.1098/rstb.2007.0015Published online 12 February 2008One contribution of 27 to a Theme Issue ‘Climate change and thefate of the Amazon’.* Author for correspondence ( [email protected]).1773 This journal is q 2008 The Royal Society(2006) and Araga˜o et al. (2007). They suggest that the2005 drought was characterized by the intensificationof the dry season in southwestern Amazonia, favouringconditions for the propagation of fires; at the time thelevels of many rivers in the region were below normal.During 2005, the annual cumulative number of fires inAmazonia increased 33% in relation to the 1999–2005mean. In the State of Acre, at the centre of the 2005drought, the area of leakage forest fires was more thanfive times greater than the area directly deforested. Fireleakage into flammable forests may be, therefore, themajor agent of biome transformation in a scenario ofincreased drought frequency in this region.The present study focuses on the hydro-climaticcharacteristics of the 2005 drought in Amazoniaextending on the observational analyses from Marengoet