Regional climate change over southern South America: evolution of mean

climate and extreme events

Silvina A. SolmanCIMA (CONICET-UBA)

Buenos AiresARGENTINA

1st Ibero-American Workshop on Climate Dynamics, Climate Change and Regional Climate Modeling, Sao Paulo, Brasil 20-23 August 2007

Why a regional simulation is needed over southern South America?

Why a Regional Model is needed over southern South America?

Goals

To assess the capability of the regional model to simulate present-day regional climate over southern South America

To identify systematic model errors To determine the added value of using a

regional model To derive the regional climate change pattern

mean climatic conditionsseasonal cyclesextreme events

• A series of regional climate simulations performed with the MM5 (Fith-generation Pennsylvania State University-NCAR /Penn State- NCAR) regional model nested within time-slice global atmospheric model experiments conducted by the HadAM3H (Hadley Centre). model for different periods:

– 1981-1990 Present climate– 2081-2090 SRES A2– 2081-2090 SRES B2

Regional scenarios of climate change over southern South America

Present climate simulation

• Low-low level circulation patterns– SLP, 850 hPa winds

• Surface variables– Precipitation– Mean, Maximum and Minimum temperatures

Solman et al, 2007 Clim Dyn)

850 hPa wind (1981-1990)HadAM3H NCEP MM5

westerlies LLJ

Precipitation: Annual cycle

HadAM

CRU

MM5

Extreme events: Precipitation

• 95th percentile

• Wet day freq

MM5

HadAM

Observations

CRU

MM5

HadAM

Observations

CRU

Temperature: Annual cycle

CRU

MM5

Regional simulation: Main biases

• Model biases can be related to both deficiencies in the regional model configuration and deficiencies in the boundary conditions• The location and intensity of the Chaco Low (topographically-induced systems) is not well simulated affecting the moisture advection over La Plata basin and, in consequence, rainfall is underestimated over the region • West of the Andes overestimation of rainfall is related mainly to biases in the boundary conditions, which tend to produce too strong westerlies, and, in consequence, enhanced synoptic scale variability over the Pacific storm-track • Biases in mean and maximum temperatures are consistent with biases in precipitation: negative (positive) biases are found over regions where rainfall is overestimated (underestimated)• The regional model improves the simulation of extreme events compared with the global model

Regional scenarios: A2 – B2

Regional scenarios: Changes in mean climate SLP

Nuñez et al. (2007)

Changes in mean climate

Present

A2

B2

Changes in mean climate: Precipitation

Changes in extreme events: Precipitation

Present climate

A2

B2

Changes in extreme events: Precipitation

Present climate

A2

B2

Changes in extreme events: Precipitation

Present climate

A2

B2

Changes in extreme events: Precipitation

Present climate

A2

B2

Changes in mean climate

Present

A2

B2

Changes in mean climate: Temperature

Present

A2

B2

Final remarks: Regional scenarios of climate change

• A southward extension of the summer mean Atlantic and Pacific subtropical highs

• Stronger westerlies, mainly during JJA• A general increase in precipitation in northern and central Argentina

especially in summer and fall • Increasing precipitation is mainly due to more intense extreme

events rather than more rainy days • A general decrease in precipitation in winter and spring mainly due

to less rainy days• Large increase in precipitation over the southern Andes during

winter and increase in extreme events• Large decrease in precipitation over subtropical andes during winter

and decrease in the frequency of wet days• In the two scenario runs the warming in southern Brazil, Paraguay,

Bolivia and northeastern Argentina are larger in winter • Over southern regions the warming is weaker• Minimum temperatures rise is larger than maximum temperatures

rise.