Dynamics of climatic hazards in northeast Brazil

Abstract

Departure characteristics of the large-scale circulation are studied in relation to extreme drought and flood years in northeastern Brazil identified from a collective of long-term rainfall stations and series of river discharge. Ship observations during 191 1--72 compiled with a one degree square resolution and extending between 30"N and 30"s from the African coast to the eastern Pacific form a major observational basis.The rainy season of northeastern Brazil is narrowly centred around March/April and is related to the southernmost seasonal migration of a lower-tropospheric confluence axis over the adjacent eastern tropical Atlantic. The 'S&cas' of CearA province are characterized by an equatorward expansion of the South Atlantic, and a poleward retraction of the North Atlantic, highassociated with a northward displacement of the enclosed near-equatorial trough of low pressure. Concurrently, the zonally oriented bands of maximum cloudiness and precipitation frequency stay farther north, the North Atlantic trades weaken, and the South Atlantic trades become stronger than in the long-term mean. The sea surface temperature pattern during a deficient rainy season in northeast Brazil is characterized by positive departures in a broad band across the North Atlantic and in the eastern Pacific, and anomalously cold waters in most of the South and equatorial Atlantic. During abundant rainy seasons in northeast Brazil, departure patterns are approximately inverse to those typical of drought years.A strong negative linkage exists between northeast Brazil rainfall and sea surface temperature along the Ecuador/Peru coast. This seems to be caused by inverse long-term pressure variations over the eastern South Pacific and South Atlantic oceans, which in turn may be part of large-scale mass adjustments of the Southern Oscillation type.Development of the equatorward expansions of the North and South Atlantic highs, pre-season precipitation in northeast Brazil and the Guayanas, and location of the cloudiness and precipitation belts over the adjacent western tropical Atlantic, are among the more promising predictors for seasonal foreshadowing of extreme rainy season behaviour in northeast Brazil.

The role of North Brazil Current transport in the paleoclimate of the Brazilian Nordeste margin and paleoceanography of the western tropical Atlantic during the late Quaternary

“…Likewise, anomalously warm conditions in the southern tropical Atlantic tend to delay the northward migration of the ITCZ and generate wetter-than-normal conditions in the northern Nordeste. These precipitation anomalies can occur on a variety of timescales including intra-annual (e.g., Marengo et al, 2008 andLewis, et al, 2010), decadal (e.g., Hastenrath andHeller, 1977 andShukla, 1996), and, perhaps, centennial/millennial (e.g., Cruz et al, 2009 and this paper). Thus, we posit that the centennial-millennial detrital-rich intervals represented by the Ti/Ca peaks were produced by centennial-millennial increases of regional rainfall that coincided with a cooler northern tropical Atlantic, warmer southern tropical Atlantic, and an anomalously southward-displaced mean position of the ITCZ.…”

“…Precipitation in the northern Nordeste during the instrumental period has long been related to, and is well correlated with, oceanographic conditions offshore (e.g., Hastenrath and Heller, 1977, Hastenrath, 1991, Ward and Folland, 1991and Nobre and Shukla, 1996. The majority of annual rainfall in the northern Nordeste occurs in March and April, when the ITCZ annually reaches its southernmost position.…”

Climate prediction for Brazil's Nordeste by empirical and numerical modeling methods

“…Building on diagnostic explorations since the 1970s, empirical prediction of Nordeste rainfall has been developed, culminating in a decade-long sequence of seasonal forecasts in real time (Hastenrath and Heller, 1977;Hastenrath et al, 1984;Hastenrath and Greischar, 1993a;Greischar and Hastenrath, 2000;Moura and Hastenrath, 2004). Adequate lead time being essential for practical applications, forecasts of the March-June rains need to be issued in the first days of February.…”

The global footprint of persistent extra‐tropical drought in the instrumental era

“…In contrast, equatorial east Africa (Tanzania, Kenya and Somalia), and the region encompassing southernmost India and Sri Lanka, are consistently dry during mid-latitude droughts. Precipitation over northeast Brazil is greatly influenced by both tropical Atlantic SSTs and tropical Pacific SSTs (Hastenrath and Heller, 1977;Moura and Shukla, 1981) and does not fall easily into the global pattern.…”