Climate Sense

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] 92

Seasonal climate forecasts and

satellite information: improving decisions

in the Uruguayan agricultural sector

Walter E. Baethgen, International Research Institute for Climate and Society, The Earth Institute at Columbia University;

and Agustín Giménez, GRAS, National Institute of Agricultural Research, Uruguay

ruguay’s economy is largely dependent – directly or indi-

rectly –on agriculture including crops, livestock and forests.

The country’s agricultural production is centred on the

highly-fertile soils of the Pampas, an ecosystem in which temper-

ate and subtropical grasslands are used for livestock production,

or have been converted to improved pastures and croplands. Large

interannual and interseasonal climatic fluctuations in Uruguay

result in high variability in crop and pasture production, as well as

having a potentially severe effect on the economy.

Southeast SouthAmerica has an established El Niño-SouthernOscillation

(ENSO) signal and, therefore, it has reasonable climate predictabil-

ity – especially during the austral spring and early summer months.

Precipitation in this region tends to be above or below normal during

years with warm or cold ENSO events, respectively. In addition, some

research results suggest that the impacts of La Niña are stronger and/or

less variable – in both rainfall and crop yields – than the impacts of El

Niño.

Regarding the impact of ENSO phases on temperature, the very

few studies conducted in Uruguay suggest that the temperature ampli-

tude in northern Uruguay is reduced in El Niño years. The studies also

suggest that mean temperatures in the whole country tend to be lower in

La Niña years in all months, with a few exceptions during the summer.

Recent La Niña-related droughts in Uruguay

Two La Niña episodes, during 1988-1989 and 1999-2000, had strong

negative impacts on the Uruguayan economy. Both episodes were char-

acterized by extended periods with reduced rainfall that strongly affected

the agricultural sector.

One of the most critical rainfall periods for agriculture in Uruguay is

late spring and summer (October-February). Average rainfall conditions

during the summer months, 90-130 millimetres a month depending on

location, are typically insufficient to compensate for evapotranspiration

losses. Therefore, pasture and crop growth greatly depends on the soil’s

ability to store water. Natural grasslands in Uruguay occupy more than 70

per cent of the total land area and are mostly located in the northern and

central regions of the country. Soils in these regions are frequently shallow

(less than30 centimetres indepth), and therefore possess lowwater storing

capacity. Pasture production in these regions is thus highly dependent on

the rainfall that comes during the late spring and summer months.

On the other hand, annual summer crops (for example maize,

sorghum, sunflower and soybeans) require adequate rainfall during the

critical flowering growth stage. Maize in Uruguay is grown in deep soils

with relatively large water holding capacity. However, the

amount of stored water in these soils is typically insufficient

to satisfy the crop water demand, and yields of non-irri-

gated crops strongly depend on rainfall during the flowering

months of late December and January.

In summary, good years in Uruguay for natural grass-

lands in shallow soils and for annual summer crops in

deeper soils are characterized by larger than normal rainfall

during late spring and summer. In the two most recent La

Niña episodes (1988-1989 and 1999-2000), rainfall during

these critical periods was considerably below average.

Although the total land area of Uruguay is relatively small

(approximately 190,000 square kilometres), large spatial

variability is typically found in the spring and summer

rainfall across the country’s regions. For example, in both

1988-89 and 1999-2000 rainfall in spring and summer

was much lower in the northwest than in the southwest

or central regions. Also, the negative rainfall anomalies

in 1999-2000 started earlier and lasted longer than in the

1988-89 period.

Responses in the agricultural sector to the 1988-1989

and 1999-2000 droughts

In 1988Uruguay had no institutional structures, special poli-

cies or programmes in place to respond to droughts. At that

time droughts were viewed as very low frequency phenom-

ena that did not justify the development of special structures

or programmes. As such, governments had typically reacted

to previous droughts with crisismanagement responses such

as special aid programmes for affected regions.

Research on teleconnections and impacts of ENSO on

climate in Uruguay was incipient. Ropelewski and Halpert

had just published the first article showing the correlation

between ENSO anomalies and rainfall patterns in southeast-

ern South America.

Climate scientists from the University

of Uruguay and the NationalWeather Service were only just

starting the first research studies on ENSO impacts.

The 1988-89 drought found Uruguay with no institu-

tional structures, with no capabilities to assess or monitor

water availability and with incipient research on the ENSO

impacts on rainfall. Consequently, the government and

the private sector could only respond to the drought with

overnance

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