An Observed Trend of Precipitation in the PROSUR Area of South America

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An Observed Trend of Precipitation in the PROSUR
Area of South America
Tendencia de precipitacão observada na area
PROSUR da America do Sul

Brant Liebmann Carolina S. Vera Leila M.V.
Carvalho Ines Camilloni Marty P. Hoerling Dave
Allured
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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.
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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
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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 Grande Servicio 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
Suriname METEO-France
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1976-1999 Climatology
January-March Total
December-February Total
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Index 47W-53W 23S-29S
southern Brasil
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JFM climo 1976-1981
JFM climo 1994-1999
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JFM climo difference 1994/99 minus 1976/81
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What are the characteristics of the observed
trend?
Quais são as caracteristicas da tendencia
observada?
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Slope 3.87 mm/yr
Slope -1.2 mm/yr
Slope 0.165 mm/yr
Slope 3.16 mm/yr
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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)
gt R).
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Este Central de la Amazonia
Fecha promedio de iniciación 30 de diciembre
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1 January
Average onset date 25 October
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31 March
Average onset date 25 October
Average end date 9 April
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Average onset date 25 October
Average end date 9 April
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difference
1976-1981 1994-1999
Rainy day average 14.8 17.5 Percent dry days
57.2 46.0
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Is observed precipitation trend due to a change
in synoptic variability?
Esta tendencia é devido a mudanca na
variabilidade sinotica?
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Trend in JFM daily 700 mb heat flux (1976-1999)

_
statistical significance of trend
99
97.5
95
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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)?
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Simultaneous Correlation
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Available stations - 1980
Available stations - 1948
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Slope 1976 - 1999 7.20 1948 - 1975 1.11 1948
- 1999 1.53
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Slope (m3/s/yr) 1976-1999 49.2 1948-1075
20.2 1948-1999 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))
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SST in southwest Atlantic
Jan-March rainfall
Jan-Mar SST (C)
Season rainfall (mm/yr)
Slope 1976 - 1999 0.045 deg/yr 1948 - 1975
0.022 1948 - 1999 0.022
Slope 1976 - 1999 7.20 mm/yr 1948 - 1975
1.11 1948 - 1999 1.53
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95 significant Using 2-sided t-test
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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.