Simulation of rainfall anomalies leading to the 2005 drought in Amazonia using the CLARIS LPB regional climate models

J. A. MARENGO; S.CHOU; C. MOURAO; S. A. SOLMAN; E. SANCHEZ; P. SAMUELSSON; R. P. DA ROCHA; L.LI; N.L. PESSACG; A.R. REMEDIO; A. CARRIL; I.F.CAVALCANTI; D. JACOB

CLIMATE DYNAMICS

SPRINGER

Lugar: Berlin; Año: 2013 vol. 41 p. 2937 - 2955

0930-7575

The meteorological characteristics of the drought of 2005 in Amazonia, one of the most severe in thelast 100 years were assessed using a suite of seven regional models obtained from the CLARIS LPB project. The models were forced with the ERA-Interim reanalyses asboundary conditions. We used a combination of rainfalland temperature observations and the low-level circulation and evaporation fields from the reanalyses to determine the climatic and meteorological characteristics of this particular drought. The models reproduce in some degree the observed annual cycle of precipitation and the geographicaldistribution of negative rainfall anomalies during the summer months of 2005. With respect to the evolution ofrainfall during 2004?2006, some of the models were able to simulate the negative rainfall departures during earlysummer of 2005 (December 2004 to February 2005). Theinterannual variability of rainfall anomalies for both austral summer and fall over northern and southern Amazonia show a large spread among models, with some of them capable of reproducing the 2005 observed negative rainfall departures(four out of seven models in southern Amazonia during DJF). In comparison, all models simulated theobserved southern Amazonia negative rainfall and positiveair temperature anomalies during the El Nino-related drought in 1998. The spatial structure of the simulatedrainfall and temperature anomalies in DJF and MAM 2005 shows biases that are different among models. While some models simulated the observed negative rainfall anomalies over parts of western and southern Amazonia during DJF, others simulated positive rainfall departures over centralAmazonia. The simulated circulation patterns indicate a weaker northeasterly flow from the tropical North Atlantic into Amazonia, and reduced flows from southern Amazoniainto the La Plata basin in DJF, which is consistent with observations. In general, we can say that in some degree the regionalmodels are able to capture the response to theforcing from the tropical Atlantic during the drought of2005 in Amazonia. Moreover, extreme climatic conditionsin response to anomalous low-level circulation features are also well captured, since the boundary conditions come from reanalysis and the models are largely constrained bythe information provided at the boundaries. The analysis ofthe 2005 drought suggests that when the forcing leading to extreme anomalous conditions is associated with both local and non-local mechanisms (soil moisture feedbacks and remote SST anomalies, respectively) the models are not fully capable of representing these feedbacks and hence, the associated anomalies. The reason may be a deficient reproduction of the land?atmosphere interactions.