Regional climate change over southern South America: evolution of mean climate and extreme events Silvina A. Solman CIMA (CONICET-UBA) Buenos Aires ARGENTINA 1st Ibero-American Workshop on Climate Dynamics, Climate Change and Regional Climate Modeling, Sao Paulo, Brasil 20-23 August 2007
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Regional climate change over southern South America: evolution of mean climate and extreme events Silvina A. Solman CIMA (CONICET-UBA) Buenos Aires ARGENTINA.
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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:
• 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