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South-Central U.S. Droughts and La Niña

South-Central U.S. Drought Meeting, Austin 07-07-11. South-Central U.S. Droughts and La Niña. Klaus Wolter (klaus.wolter@noaa.gov) University of Colorado, CIRES & NOAA-ESRL/PSD1 <with help from Jon Eischeid>. • Drought in south-central U.S.: Some fundamentals

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South-Central U.S. Droughts and La Niña

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  1. South-Central U.S. Drought Meeting, Austin 07-07-11 South-Central U.S. Droughts and La Niña Klaus Wolter (klaus.wolter@noaa.gov) University of Colorado, CIRES & NOAA-ESRL/PSD1 <with help from Jon Eischeid> •Drought in south-central U.S.: Some fundamentals •The association of La Niña with drought in this region •Hurricanes to the rescue? •The role of La Niña in extending drought beyond 2010-11

  2. Semi-arid NM/Western TX vs. moist Eastern TX/LA: from less than 8” near the Four Corners to over 60” in Louisiana – a deficit of, say, 10” in a year or two near the Gulf Coast carries less impact than further west…

  3. Seasonal cycle Summer monsoon (top left) contributes up to 50% of the annual precipitation in NM, but is quite unimportant from eastern TX into LA; fall season (top right) contributes > ¼ of annual totals over eastern TX; winter (bottom right) is most important in LA; spring (bottom left) is key season from eastern NM eastwards. NOTE: It is easiest to get into or out of droughts during the wettest season of the year! JAS OND AMJ JFM

  4. A quick look at Texas drought history: the 1950s ‘Drought of the Century’ was anchored by repeated La Niña conditions, and was much more severe and prolonged than other droughts of the last century. Top five Texas droughts on record (Oct-Jun) are all associated with La Niña (2011, 1925, 1956, 1917, 1971).

  5. http://www.esrl.noaa.gov/psd/enso/mei/ Multivariate ENSO Index (MEI; top) is based on weighted average of sea level pressure, zonal & meridional wind components, sea surface temperature, air temperature, total cloudiness in tropical Pacific. Remarkable drop in early 2010 from mid-sized El Niño to biggest La Niña event in 35 years in just half a year -

  6. http://www.esrl.noaa.gov/psd/enso/mei/ Multivariate ENSO Index (MEI; top) is based on weighted average of sea level pressure, zonal & meridional wind components, sea surface temperature, air temperature, total cloudiness in tropical Pacific. Remarkable drop in early 2010 from mid-sized El Niño to biggest La Niña event in 35 years in just half a year – are we seeing an opposite transition to El Niño in 2011? Not so fast…

  7. http://www.esrl.noaa.gov/psd/enso/mei/ Multivariate ENSO Index (MEI; top) is based on weighted average of sea level pressure, zonal & meridional wind components, sea surface temperature, air temperature, total cloudiness in tropical Pacific. Strong La Niña events tend to last more than one year! <more recent events of 1998-2001 and 2007-09 confirmed this tendency>

  8. Niño 3.4 Most recent ENSO conditions: central tropical Pacific is sitting on fence, some trade winds are stronger than normal, some weaker (top); on the other hand, there is a subsurface reservoir of cold water that could anchor a comeback later this year…

  9. Seasonal cycle of ENSO impacts New Mexico has positive correlations year-round, but most pronounced in winter and spring (bottom panels). Texas correlates highest in winter (bottom right). Summer and fall are much less constrained by the phase of ENSO. Louisiana shows negative correlations in summer (top left), while the other three seasons favor positive correlations, especially in winter.

  10. What happens during moderate-strong Las Niñas similar to the last one? Typically dry over southwestern U.S., especially New Mexico How unusual was 2010-11? Unusually wet northwest of Southern CA, northern AZ, central CO, extremely dry to SE, i.e. NM, TX and LA.

  11. What can we expect this summer? Little preference for wet or dry conditions; only 1951 and 1976 had switched to El Niño by this time of year (2000 and 2008 were neutral, rest still La Niña).

  12. Statistical Forecast for July-September 2011 Skill map (below) shows decent skill over eastern CO and most of NM. The April forecast for July-September 2011 (top left) was more ‘optimistic’ for southwestern U.S. than the most recent update (top right). This is based on more information than just the state of ENSO.

  13. Statistical Forecast for July-September 2011 Skill map (below) shows decent skill over eastern CO and most of NM. The April forecast for July-September 2011 (top left) was more ‘optimistic’ for southwestern U.S. than the most recent update (top right). This is based on more information than just the state of ENSO. ‘Wild cards’ in 2011: 1. Record-snowpack (might impede reach of monsoon); 2. Wildfires (could suppress monsoon á la 2002); 3. Rapid (re-)development of El Niño (La Niña) could add (reduce) moisture

  14. What can we expect in the next five days? Expected total precipitation, according to Hydrological Prediction Center (NOAA-HPC) –monsoon looks active, leaving Texas and eastern NM continued dry…

  15. What can we expect next week and beyond? European & U.S. models show ‘normal’ summer monsoon flow pattern, funneling moisture from AZ into CO and western NM, with little hope for regions further east…

  16. Hurricanes to the rescue? There were 9 recorded cases of land-falling hurricanes in 9 post-La Niña summers and falls along Western Gulf Coast (TX, LA) out of 34 in total (in 61 years) - a doubled risk of this type of event, but four out of the nine years had no such event either.

  17. Monthly rainfall anomalies in wake of landfalling hurricanes Edith Flossy Fern Carmen

  18. Monthly rainfall anomalies in wake of landfalling hurricanes Chantal Jerry Gustav Ike Dolly

  19. We know from Tropical Storm Allison that dumped 40” of rain on Houston in early June 2001 that a tropical storm does not have to reach hurricane status to cause a lot of rain/damage…

  20. What can we expect in the upcoming winter/Water Year? Left figure: Strong La Niña PLUS one year Bottom: All two-year La Niña cases for Year 2 (overlap: 50-1, 71-2, 74-5, 89-90, 08-09) If we slip back into La Niña, it increases the chances for another drought winter in all of the south-central U.S.

  21. Take Home Points • No clear end in sight for the drought in south-central U.S. • Hard to break up drought pattern, tends to self-perpetuate • Tropical storms could help out in parts of the domain, but not especially likely • Next winter leans towards dry if La Niña rebounds – more likely than not • No tools in hand to predict 50s-type drought, so, yes, we cannot rule out a seven-year drought

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