South America: Transitioning away from exceptional water deficits

November 16, 2016

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

Impacts
It's the fifth year of drought in Northeast Brazil. In September drought reached the most severe level in 12 months according to data from Northeast Brazil's Drought Monitor. One in two cities in the region is in a state of emergency and tanks supply water to 824 municipalities in drought zones at a cost of around R$ 86.8 million (US$ 27 million) per month.

In the state of Bahia the Sobradinho Reservoir on the São Francisco River - the largest reservoir in the Northeast - is at 7.1 percent of capacity. In the Northeast region known as Matopiba, once billed as the new frontier, agribusinesses are quickly retreating or switching from soybeans to more drought tolerant crops, as productivity fell 40 percent in the latest season.

Record rainfall in Argentina has flooded corn, wheat, and soybean fields, for the second time in seven months for some regions. In March and April flooding caused extensive losses in central and eastern regions of the country, and in October around 600,000 hectares of southern farmland flooded in northwestern Buenos Aires, north-central La Pampa, and southern Cordoba. The wheat crop may have been completed destroyed, corn may need to be replanted, and soybean planting has been delayed.

Forecast Breakdown
The 3-month maps (below) for the same 12-month period illustrate the forecast of a transition away from widespread exceptional deficits observed August through October – particularly in the Amazon Basin – to some moderate surplus in the Basin and much diminished intensity and extent of deficits elsewhere across the continent.

However, from November through January pockets of extreme to exceptional deficits are forecast in parts of western Amazonas and central Brazil, the Cordillera Real Mountains of Bolivia, and scattered down through nations along the Pacific Ocean, particularly Chile. Deficits of lesser severity are forecast in northern Venezuela; northeastern Brazil and farther south around São Paulo and Rio de Janeiro; and southern Argentina.

Moderate surpluses are forecast November through January for part of the Amazon Basin from, roughly, Manaus in the west to the Jari River in the east at the border of Amapá, and in the Paraguay River Basin through eastern Paraguay into Argentina. Moderate to extreme surpluses are forecast in central and eastern Colombia and northern Bolivia. A large pocket of extreme to exceptional surplus is expected to persist in La Pampa, Argentina, and both deficits and surpluses are forecast for the Desaguadero and Colorado River Basins.

As the forecast moves into February through April, yellow and pale orange replaces brighter shades in most places, indicating a forecast of diminished water deficits. Chile remains the exception with areas of significant deficit still evident though overall extent is reduced.

The forecast for the latter months – May through July – shows a pattern similar to the prior three months but with an increasing extent of water deficits, particularly along the northern Pacific coast.

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