Understanding physical processes linked to climate

variability and change in the South America Monsoon

System

Carolina Vera1, C. Junquas 1,2, H. Le Treut 2, L. Li 2

1CIMA/CONICET-University of Buenos Aires and DCAO/FCEyN,, Buenos Aires,

Argentina

2 LMD/IPSL, Paris, France 1

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Precipitation changes as

depicted by the WCRP/CMIP3 multi-model ensemble (IPCC-AR4,

2007)

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Which are the physical mechanisms explaining an

increase of summer precipitation in

southeastern South America under GHG increment

scenario?

4DJF climatological mean precipitation

(CMAP)

SACZSouth

Atlantic Convergenc

e zone

LPBLa Plata

Basin

Leading pattern of year-to-year variability of DJF precipitation anomalies (CMAP)

EOF1 - domain A

EOF1 - domain B

A

B

5

•To explore changes in the leading pattern of precipitation year-to-year variability in South America in the context of a climate change induced by GHG increment.

•To explore how much of those changes account for the trends projected for austral summer precipitation in southeastern South America

OBJECTIVES

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• 18 models from (WCRP/CMIP3) dataset for IPCC-AR4 are used.

• For each model, EOF analysis of DJF precipitation anomalies from XXI century simulations is performed over southeastern South America.

Data and Methodology

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Leading pattern (EOF1) of DJF rainfall anomaly variability

from the 18 models

Period: 2001-2099

Scenario: SRESA1B

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Principal Components (PC1) of EOF1 from two of the models

•Blue (red) : PC1 larger (smaller) than 1 (-1) standard deviation Positive(Negative) EOF1-SE.

•Positive (negative) EOF1-SE are associated with positive (negative) precipitation anomalies in LPB

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Changes in the number of positive and negative EOF1-SE

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Mean number of

positive and negative EOF1-SE

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Increment of wetter than

normal DJFs in the la Plata Basin

Decrease of dryier than normal DJFs

in the la Plata Basin

Mean number of positive

and negative EOF1-SE

9 models were selected that show: i) a realistic representation of the dipole-like structure associated to EOF1 events in the present (not shown) as in the future

ii) an increase of the projected summer rainfall in LPB by the end of the 21st century .

iii) an increase of the frequency of positive EOF1 events and adecrease of negative EOF1 events during the 21st century

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DJF rainfall difference between (2050-2099) and (2001-2049)

EOF1-SE years(~30% of year total)

no EOF1-SE years

9-model ensemble

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All years

The differences in the three panels are

standardized by the total number of years

Temporal evolution of the DJF normalized rainfall anomalies in LPB (38°S-26°S,64°-50°W) from 9-model

ensemble

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Blue (red) dots correspond to the rainfall anomalies associated to each of the positive (negative) EOF1 events identified for each of the models (the corresponding linear trends are depicted in dashed lines)

Composite differences of mean DJF SST anomalies between positive and negative EOF1 events from the 9-model ensemble

mean

(A) 2001-2049 (B) 2050-2099

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(B) –(A)

Composites of standardized SST anomalies for positive and negative EOF1 events over the central Tropical Pacific Ocean from 9-model

ensemble

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Warmer than normal Central Pacific

conditions associated to an increment of wetter than normal summers in the la

Plata Basin

Composite differences of DJF geopotential height anomalies at 500 hPa between positive and

negative EOF1events from 9-model ensemble

2001-2049

2050-2099

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Composite differences of moisture fluxes (arrows) and their divergence (contour) at 850 hPa between positive

and negative EOF1 events from 9-model ensemble

2001-2049

2050-2099

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•How much of the results are related to the ability of current climate models in correctly reproducing the tropical ocean dynamics not only in the Pacific but also in the Atlantic basins?

•Which is the role of other sources of climate variability (Indian Ocean, SAM) in explaining such trends?

•Which is the combined effect of GHG increment and land use change on the regional climate change?

•How will natural climate variability signal combine with that associated to climate change in the next decades?

Discussion

Annual mean anomalies of precipitation in Posadas (Northeastern Argentina)

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•How much of the results are related to the ability of current climate models in correctly reproducing the tropical ocean dynamics not only in the Pacific but also in the Atlantic basins?

•Which is the role of other sources of climate variability (Indian Ocean, SAM) in explaining such trends?

•Which is the combined effect of GHG increment and land use change on the regional climate change?

•How will natural climate variability signal combine with that associated to climate change in the next decades?

Discussion

Strategy•Analysis of CMIP5 multi-model ensemble simulations•New sensitivity studies performing numerical simulations with global and regional models at specific conditions