An Observed Trend of Precipitation in the PROSUR Area

of South America

Brant LiebmannCarolina S. VeraLeila M.V. CarvalhoInes CamilloniMarty P. HoerlingDave Allured

Tendencia de precipitacão observada na area PROSUR da America do Sul

Se um evento de inundacão esta definido

como dois desvios-padrão da anomalia mensal do fluxo em

Corrientes, Argentina, então existem quase

seis vezes mais inundacões nos 20 anos

entre 1980-1999 que existiram nos 60 anos

entre 1920-1979.

Previous work:

Barros, Castaneda, Doyle (2000): Increase in precipitation over most of Argentina from 1956-1991. Decrease in meridional temperature gradient.

Castaneda and Barros (1994): Humid Pampa increase in rain, mainly after 1960.

Vargas (1987):

Grimm:

Marengo:

Data We wish to thank the following agencies for providing

the data used in this study:Agência Nacional de Águas (Brasil)

Agência Nacional Energia Elétrica (Brasil)U.T.E. Uruguay

C.T.M. Salto GrandeServicio Meteorologico Nacional (Argentina, Paraguay,

Uruguay)FUNCEME (Ceará, Brasil)SIMEPAR (Paraná, Brasil)DAEE (São Paulo, Brasil)

Minesterio del Ambiente y los Recursos Naturales (Venezuela)

Meteorogische Dienst SurinameMETEO-France

1976-1999 Climatology

January-March Total December-February Total

Index: 47W-53W23S-29S

“southern Brasil”

JFM climo 1976-1981 JFM climo 1994-1999

JFM climo difference – 1994/99 minus 1976/81

What are the characteristics of the observed trend?

Quais são as caracteristicas da tendencia observada?

Slope = 3.87 mm/yr

Slope = 3.16 mm/yr

Slope = 0.165 mm/yr

Slope = -1.2 mm/yr

1

( ) ( ( ) )dia

n

A dia R n R

A(dia) = Acumulación anómala

R(n) = lluvia diaria

R = promedio anual de precipitación diaria

Se considera que la estación lluviosa tiene lugar cuando la pendiente de la curva es

positiva (R(n) > R).

Fecha promedio de iniciación: 30 de diciembre

Este Central de la Amazonia

Average onset date = 25 October

1 January

Average onset date = 25 October Average end date = 9 April

31 March

Average onset date = 25 October Average end date = 9 April

difference

Rainy day average = 14.8 17.5Percent dry days = 57.2 46.0

1976-19811994-1999

Is observed precipitation trend due to a change in synoptic variability?

Esta tendencia é devido a mudanca na variabilidade sinotica?

statistical significance of trend

95%

97.5%

99%

Trend in JFM daily 700 mb heat flux (1976-1999)

_

+

Is there a relationship between observed precipitation trend and sea

surface temperature?

Esta tendencia observada na precipitacão esta relacionada a temperatura da

superficie do mar (TSM)?

Simultaneous Correlation

Available stations - 1980 Available stations - 1948

Slope:1976 - 1999 = 7.201948 - 1975 = 1.111948 - 1999 = 1.53

Slope (m3/s/yr):1976-1999 = 49.21948-1075 = 20.21948-1999 = 17.2

Precipitation has increased by 35% (along trend line)River flow has increased by 161%

(amplification and delay noted by Berbery and Barros (2002))

Slope:1976 - 1999 = 0.045 deg/yr1948 - 1975 = 0.0221948 - 1999 = 0.022

Slope:1976 - 1999 = 7.20 mm/yr1948 - 1975 = 1.111948 - 1999 = 1.53

SST in southwest AtlanticJan-March rainfall

Sea

son

rain

fall

(mm

/yr)

Jan-

Mar

SS

T

(C)

95% ‘significant’Using 2-sided t-test

An observed positive precipitation trend during the rainy season in Southern Brazil is most prominent from 1976-1999, but is evident earlier.

The trend is consistent with a change in river flow.

The trend is characterized by an increase in the number of rainy days per season and an increase in the amount per rainy day.

The precipitation trend is related to one in SST, although perhaps not causally.

The SST trend seems to result from a decrease in the strength of the South Atlantic high.