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

I  

“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?)