Climate Exchange

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show an absolute minimum for the summer months

(December-February), while a very significant

increase is observed during the autumn. The decrease

in rainfall during winter is observed in the southern

part of the basin where flows are lower during August

and September. Surges of flows associated with the

arrival of the spring rainy season can be seen from

October onwards in the basin.

It is characteristic of the basin that river flow is regu-

lated by evapotranspiration in the summer months and

by rainfall in the winter months. The El Niño Southern

Oscillation (ENSO) also influences rainfall and climate

patterns. The warm phase of ENSO causes strong posi-

tive anomalies from October to December whereas the

cold phase shows significant negative anomalies in the

same period.

A strong ENSO warm phase effect was experienced

in 1997-1998 with exceptionally high rainfall events

between October 1997 and January 1998. In 2008-

2009, the opposite was observed.

Hydropower generation in Uruguay

From 1965 to 2011, total electricity consumption

(demand) has been growing at an annual average of 4

per cent. Until 1980, the demand was supplied using

thermal and hydro generation in similar percentages.

With the incorporation of the Salto Grande power

station in 1981 and Constitución in 1983, national

electricity production began to be greater than the

total demand and the surplus energy was exported to

Argentina and Brazil.

Periods of above- or below-normal rainfall can cause energy prices to fluctuate

Image: Tamara Avellán WMO

Climate variability of the Uruguay basin

Time series observed during the past 30 years indicate signifi-

cant variability in the amount of rainfall in the basin. The

decade 1993-2002 was the wettest, while 2003-2011 showed

frequent dry events. The monthly mean flows for 1979-2010

Source: IRI

Rainfall probabilities associated with ENSO