Understanding and Explaining Causes for Trends in Regional ... · Science Review 12-14 May 2015...
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Science Review 12-14 May 2015 Boulder, Colorado
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Martin Hoerling
Understanding and Explaining Causes for Trends in Regional Precipitation
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Got Forcing? What Forcing? What’s Next? 2
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Characterizing Observed Precipitation Trends
Hoerling, Eischeid, Perlwitz 2010 J. Climate 3
I
“Its Ge(ng Drier”
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Characterizing Observed Precipitation Trends
US Climate Change Science Program, SAP 1.3 ( Dole - Product Lead; Hoerling - Convening Lead; Ch. 3) 2009 4
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“Its Dry….Again”
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Characterizing Observed Precipitation Trends
Assessment of Climate Change in the Southwest US, CH3: Hoerling et al. 2013; Nowak et al. J. Climate 2012 5
“Its Ge(ng Drier”
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Characterizing Observed Precipitation Trends
Assessment of Climate Change in the Southwest US, CH3: Hoerling et al. 2013; Nowak et al. J. Climate 2012 6
“It’ll Get We7er Again”
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Observed Precipitation: 1901-2014
Extended Dry & Wet Regimes are Symptoms of the Semi-Arid West
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Observed Precip & SST – 1901-2013
Got Forcing? 8
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Observed Precip & SST – 1901-2013
Are Wet and Dry Regimes Determined by Warm and Cold Ocean Regimes?
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Historical Simulations (AMIP) : 1871-2013
Hoerling, Quan, Eischeid 2009 GRL ; Seager and Hoerling 2014 J Climate 10
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Historical Simulations (AMIP) : 1871-2013
SST-Forced Dry and Wet Regimes Most Prevalent in the Semi-Arid West 11
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Historical Simulations (CMIP) : 1921-2013
What’s the Nature of the Forcing?
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Historical Simulations (CMIP) : 1921-2013
Shin and Sardeshmukh 2011 Clim Dyn; Hoerling et al. 2012 J Climate
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Southwest US Precipitation Regimes of Last Century Have Not Been Strongly Forced 14
OBS AMIP CMIP
OBS AMIP CMIP
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
Southern Great Plains Precipitation Regimes of Last Century Have Been More Strongly Forced
OBS AMIP CMIP
OBS AMIP CMIP
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
We’re Getting Smarter : Improved Situational Awareness 16
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
We’re Getting Smarter : Improved Situational Awareness 17
What’s Next?
N O A A R E S E A R C H • E S R L • P H Y S I C A L S C I E N C E S D I V I S I O N
We’re Getting Smarter : Improved Situational Awareness 18
What’s Next?
° It’s likely that sea surface temperatures have forced mulL-‐decadal trends in NA precipitaLon during the last century, especially over the southern GPlains. ° The consequenLal SST forcing has mostly been due to natural internal variability. (Contrast with Hoerling et al. 2012 for Mediterranean Pcpn trends)
° The parLcular history of SST variaLons has very likely been more important than the parLcular history of external radiaLve forcing. (Is this true for East Africa drying? See Liebmann et al. 2014)
° Appreciable precipitaLon trends arise without forcing, via atmospheric noise/land coupling alone. (Is this the paradigm for Mega-‐droughts of the American Southwest?)