South America: Exceptional deficits along Brazil's northeastern coast

October 24, 2016

The Big Picture
The forecast through June 2017, as seen in the 12-month map (below), shows some pockets of exceptional water deficits (greater than 40 years) in northern Venezuela, northern Brazil, the Cordillera Real Mountains of Bolivia, Chile, and along rivers in southern Argentina. Surpluses are forecast for central Colombia, much of Bolivia, in northwestern Argentina and the Desaguadero River basin.

Impacts
Sheep farmers in Argentina's North Patagonia are suffering the worst drought in 17 years and are anticipating poor spring forage with rainfall so far this year 45 percent below average. A report from the University of Buenos Aires Agronomy School and INTA (Agriculture Technology Institute) is recommending immediate and drastic reduction of flocks. The region includes the provinces of Rio Negro and Chubut where 43 percent of the country's sheep are raised.

The water level at Guri dam, which supplies 63 percent of Venezuela's hydroelectric power, measured 262.89 meters in late September, below the optimum performance level of 271 meters. With the rainy season now over the water level is not expected to increase, raising the specter of a return to electricity rationing in 2017. A 40-day ration period was imposed earlier this year in 10 of 23 states.

Forecast Breakdown
The 3-month maps (below) for the same 12-month period illustrate the forecast of a transition away from widespread exceptional deficit observed July through September – particularly in the Amazon – to moderate surplus.

However, moderate to severe deficits are forecast October through December in an arc across northern Brazil from Amazonas to Pará, then becoming exceptional along Brazil’s northeast coast from Amapá through Rio Grande do Norte. Moderate deficits are forecast from Rio de Janeiro south. Beyond Brazil, other areas with a forecast of exceptional deficits include many parts of Chile, rivers in southern Argentina, Tierra del Fuego, and the Falkland Islands. Deficits are also expected during this period in northern Venezuela, northern Suriname, French Guiana, western regions of Colombia, Ecuador and Peru, and the Cordillera Real Mountains in western Bolivia.

Moderate to extreme surpluses are forecast October through December in central and eastern Colombia, northeastern Ecuador, watersheds of northern Peru, and northern Bolivia. Primarily abnormal (3 to 5 years) surpluses are forecast for central Brazil. Exceptional surpluses are forecast for northwestern Argentina, and both deficits and surpluses are forecast for the Desguadero and Colorado River Basins.

From January through March northern Brazil is forecast to transition from deficit to moderate surplus. Moderate surpluses are expected to emerge in southern Venezuela and to persist in central and eastern Colombia, in Bolivia, and in central Paraguay. Though extreme deficit conditions are forecast to persist in a few areas – small pockets in Chile and rivers in southern Argentina – no areas of exceptional deficit are forecast.

The forecast for the latter months – April through June – shows a pattern similar to the prior three months.

(It should be noted that forecast skill declines with longer lead times.)