Texas Drought: The Long and the Short of It

1. Texas Drought: The Long and the Short of It John W. Nielsen-Gammon Texas State Climatologist Texas A&M University n-g@tamu.edu

5. Rank of 2011 for 6-12 month accum- ulated precipitation through July Dark red = driest out of 100 Yellow = driest 10%

6. Worst year for 6-12 month accumulated precipitation through July

14. Sea Surface Temperature Anomalies: El Nino Years

15. El Nino Cool-Season Precipitation

17. El Nino Cool-Season Temperature

19. La Nina Cool-Season Precipitation

21. La Nina Cool-Season Temperature

23. Texas Summer Drought Feedback • Dry soil • Very little evaporation • Few thunderstorms • Drier soil • Even less evaporation • Even fewer thunderstorms • Dry soil • Very little evaporation • Plenty of heating • Hot temperatures • Even more evaporation • Even greater water demand

24. Texas Summer Drought Feedback • Hot temperatures • High pressure aloft • Air from desert southwest circles overhead • Even fewer thunderstorms • Even hotter temperatures • Tropical disturbance • Tropical wave • Tropical depression • Tropical storm • Hurricane • Widespread rain • Lower temperatures • More water vapor • More thunderstorms • Cycle is broken

25. Dryness contribution to hot summer: 4.0 +/- 0.6 °F

27. How to Make a Drought • Start with La Nina • Enhance with warm Atlantic • Subtract luck • Dry out soil and keep it dry • Repel tropical disturbances • Enhance with global warming • Repeat

32. Jet Stream Anomalies, Winter 2010-2011

33. Jet Stream Anomalies, Spring 2010-2011

34. October-December

35. Driest in 30 years Tenth-driest in 30 years Tenth-wettest in 30 years Wettest in 30 years 33% 33% 33% 40% 33% 27%

36. Driest in 30 years Tenth-driest in 30 years Tenth-wettest in 30 years Wettest in 30 years 33% 33% 33% 27% 33% 40%

39. Pacific Texas Atlantic

40. Precipitation • Not necessarily decreasing • Probably not becoming more variable • Droughts more frequent now because of PDO and AMO (or AMO-Atl?) • No blame for climate change (that we know of, yet…)

41. Drought Causes • La Niña (trigger) • Soil moisture feedback and high desert air • Warm Atlantic (moisture magnet) • Climate change (1-1.5 °F add-on)

42. Drought Outlook • Returning La Niña • Drought likely to continue • Period of drought susceptibility • Global patterns favor drought • Period will last another 5-15 years • Recent past: dry years interspersed with very wet years • Same thing going forward, or drought that lasts several years?

43. Contact Information • John W. Nielsen-Gammon • n-g@tamu.edu • 979-862-2248 • http://atmo.tamu.edu/osc • http://blog.chron.com/climateabyss