# Presentation: 810269

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

- Brant Liebmann
- Carolina S. Vera
- Leila M.V. Carvalho
- Ines Camilloni
- Marty P. Hoerling
- Dave 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 

- 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 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*

## 1976-1999 Climatology

- January-March Total

- December-February Total

## “southern Brasil”

- Index:	47W-53W
- 	23S-29S

- “southern Brasil”

**Notes:**
Trend is from 2.5 degree data, index is from 1 degree data

## 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 = 

- Slope =
- 3.87 mm/yr

- Slope =
- 3.16 mm/yr

- Slope =
- 0.165 mm/yr

- Slope =
- -1.2 mm/yr

**Notes:**
Monthly rain data /home/bl/util/gridrainindex/monthly.totals.point1.1deg
From rain gridded rain index 47-53W, 23-29S

## A(dia) = Acumulación anómala

*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

- Fecha promedio de iniciación: 30 de diciembre

- Este Central de la Amazonia

## Slide 13

## 1 January

- Average onset date = 25 October

**Notes:**
Average rate = 6.75, onset = j day 298.5, end = 98.8, rainy season total 1086, jfm total = 571

## 31 March

- Average onset date = 25 October

- Average end date = 9 April

**Notes:**
Average rate = 6.75, onset = j day 298.5, end = 98.8, rainy season total 1086, jfm total = 571

## Average onset date = 25 October

- Average end date = 9 April

**Notes:**
Average rate = 6.75, onset = j day 298.5, end = 98.8, rainy season total 1086, jfm total = 571

## Rainy day average = 14.8   17.5

- difference

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

- 1976-1981
- 1994-1999

**Notes:**
From 110 individual stations, each with at least 20 years data 1976-1999.
Believe it or not, sum percents in each category in left = 100% (there are many more categories at low end).

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

- Esta tendencia é devido a mudanca na variabilidade sinotica?

## Slide 19

## Slide 20

**Notes:**
Std is calculated each year from daily jfm data. This is trend of that.

## +

- 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

**Notes:**
Centered at 25S, 50W, good data goes back to 1948

## Slope:

- 1976 - 1999 = 7.20
- 1948 - 1975 = 1.11
- 1948 - 1999 = 1.53

## Slide 26

## 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))

## Slope:

- 1976 - 1999 = 0.045 deg/yr
- 1948 - 1975 = 0.022
- 1948 - 1999 = 0.022

- 1976 - 1999 = 7.20 mm/yr
- 1948 - 1975 = 1.11
- 1948 - 1999 = 1.53

- SST in southwest Atlantic

- Jan-March rainfall

- Season rainfall (mm/yr)

- Jan-Mar SST (C)

## 95% ‘significant’

- Using 2-sided
*t*-test

## Slide 30

## Slide 31

## 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.