Transcript Changes in extreme events: Precipitation

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
Why a regional simulation is needed
over southern South America?
Why a Regional Model is needed
over southern South America?
Regional scenarios of climate change 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 conditions
seasonal cycles
extreme 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
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
 westerlies
 LLJ
MM5
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 (topographicallyinduced 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
Changes in mean
climate: Precipitation
Present
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 extreme
events: Precipitation
Present climate
A2
B2
Changes in mean
climate
Changes in mean
climate: Temperature
Present
A2
B2
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.