1. The US CLIVAR Working Group on Drought Siegfried Schubert (NASA/GMAO) and Dave Gutzler (Univ New Mexico) Cochairs USCLIVAR Annual Summit Annapolis, MD 15-17 July 2009

2. U.S. Membership Tom Delworth NOAA GFDL Rong Fu Georgia Institute of Technology Dave Gutzler (co-chair) University of New Mexico Wayne HigginsNOAA/CPC Marty HoerlingNOAA/CDC Randy KosterNASA/GSFC Arun KumarNOAA/CPC Dennis LettenmaierUniversity of Washington Kingtse MoNOAA CPC Sumant NigamUniversity of Maryland Roger Pulwarty NOAA- NIDIS Director David Rind NASA - GISS Siegfried Schubert (co-chair) NASA GSFC Richard Seager Columbia University/LDEO Mingfang Ting Columbia University/LDEO Ning Zeng University of Maryland International Membership: Ex Officio Bradfield Lyon International Research Institute for Climate Victor O. Magana Mexico Tim Palmer ECMWF Ronald Stewart Canada Jozef Syktus Australia Jose Marengo CPTEC/INPE Jean-Philippe Boulanger Univ. of Buenos Aires Hugo Berbery Univ. of Maryland

3. Other interested participants: Jin Huang Jin.Huang@noaa.govJin.Huang@noaa.gov Adam Sobel Max Suarez ***Phil Pegion pegion@gmao.gsfc.nasa.govpegion@gmao.gsfc.nasa.gov Entin, Jared K. Donald Anderson Rong Fu rf66@mail.gatech.edurf66@mail.gatech.edu Doug Lecomte Douglas.Lecomte@noaa.govDouglas.Lecomte@noaa.gov ***Hailan Wang hwang@climate.gsfc.nasa.govhwang@climate.gsfc.nasa.gov Junye Chen jchen@gmao.gsfc.nasa.govjchen@gmao.gsfc.nasa.gov Eric Wood efwood@princeton.eduefwood@princeton.edu Aiguo Dai adai@ucar.eduadai@ucar.edu Alfredo Ruiz-Barradas Jae Kyung E Schemm Jae.Schemm@noaa.govJae.Schemm@noaa.gov Kirsten L. Findell

4. Accomplishments DWG Web page: –http://www.usclivar.org/Organization/drought-wg.htmlhttp://www.usclivar.org/Organization/drought-wg.html –List of relevant model simulations and observational data sets Coordinated Model simulations –GMAO, GFDL, NCAR, CPC, Lamont, COLA/U Miami –Impact of SST and Land/atmosphere feedbacks –http://gmao.gsfc.nasa.gov/research/clivar_drought_wg/index.htmlhttp://gmao.gsfc.nasa.gov/research/clivar_drought_wg/index.html –Subset of data available to public –ftp://gmaoftp.gsfc.nasa.gov/pub/data/clivar_drought_wg/ftp://gmaoftp.gsfc.nasa.gov/pub/data/clivar_drought_wg/ CDPW 2008 : Focus workshop on drought (with DRICOMP) –08 Spring “USCLIVAR Variations”: US CLIVAR Drought Working Group Workshop

5. Publications –U.S. CLIVAR VARIATIONS 07 Spring: The U.S. CLIVAR Working Group on Long-term Drought – D.Gutzler and S. Schubert 08 December: Overview of the Drought Working Group 08 December: Analysis of the multi-model U.S. CLIVAR Drought Working Group Simulations – P. Pegion and A. Kumar –Special Issue in JCLIM (DWG and DRICOMP) 10 publications in various stages of review from DWG (see next slide) 10 publications in various stages of review from DRICOMP –Other: Koster, R. D., Z. Guo, R. Yang, P. A. Dirmeyer, K. Mitchell, and M. J. Puma, 2009: On the nature of soil moisture in land surface models. J. Climate, in press.

6. 1) Siegfried Schubert, and the extended drought working group: A USCLIVAR Project to Assess and Compare the Responses of Global Climate Models to Drought-Related SST Forcing Patterns: Overview and Results. Accepted (pdf). 2) Kingtse C. Mo, Jae-Kyung E. Schemm and Soo-Hyun Yoo: Influence of ENSO and the Atlantic multi-decadal Oscillation on Drought over the United States. Submitted (pdf). 3) Randal Koster, Hailan Wang, Siegfried Schubert, Max Suarez and Sarith Mahanama: Drought-Induced warming in the continental United States under different SST regimes. Accepted. 4) Hailan Wang, Siegfried Schubert, Max Suarez and Randal Koster: The Physical Mechanisms by which the Leading Patterns of SST Variability Impact U.S. Precipitation. Submitted (pdf). 5) Yochanan Kushnir, Richard Seager, Mingfang Ting, Naomi Naik, and Jennifer Nakamura: Mechanisms of Tropical Atlantic SST Influence on North American Hydroclimate Variability. Submitted (pdf). 6) Philip Pegion and Arun Kumar: Multi-model Estimates of Atmospheric Response to Modes of SST Variability and Implications for Droughts. Submitted (pdf). 7) Scott Weaver, Siegfried Schubert and Hailan Wang: Warm Season Variations in the Low-Level Circulation and Precipitation over the Central U.S. in Observations, AMIP Simulations, and Idealized SST Experiments. Accepted (pdf). 8) Kirsten L. Findell and Thomas L. Delworth: Impact of common sea surface temperature anomalies on global drought and pluvial frequency. Submitted (pdf). 9) Matias Mendez and Victor Magana: Regional aspects of prolonged meteorological droughts over Mexico. Submitted (pdf). 10) Alfredo Ruiz-Barradas and Sumant Nigam: AMIP Simulations of 20th Century North American Precipitation Variability by the Drought Working Group Models. Submitted.

7. Leading EOFs and Time series (annual mean SST - 1901-2004) Linear Trend Pattern (LT) Pacific Pattern (Pac) Atlantic Pattern (Atl)

8. Idealized Experiments NATL PacInd warmneutralcold warm wwwncw neutral nwnc cold wccncc SST Forcing patterns (warm phase) PacInd NATL

9. Annual Mean 200mb Height Response (m) Pacific WarmPacific Cold

11. Global Spatial Correlations of Annual Mean Responses Precipitation z 200mb           Agreement among models for response to Pacific is high Agreement among models for response to Atlantic is lower Agreement is higher for z200 than it is for precipitation

12. The annual and continental United States mean responses for precipitation (top panel) and surface temperature (bottom panel) for all 8 combinations of the Pacific and Atlantic patterns for the 5 AGCMs CCM3NSIPP1GFSGFDLCAM3.5 U.S. Precipitation Response (mm/day) U.S. Tsfc Response (mm/day)

13. °C Optimal SST Forcing for Drought in US

14. Annual Precipitation (mm/day) Pacific Cold+Atlantic WarmPacific Warm+Atlantic Cold US Drought!US Pluvials!

15. Precipitation Response (mm/day) During SON: PcAw mm/day

16. 850mb Wind Speed (m/s) and Streamlines During SON m/s

17. Major drought in Great Plains mm/day No Soil Moisture FeedbackWith Soil Moisture Feedback Impact of Soil Moisture Feedbacks - Response to Cold Pacific in JJA Reduced severity of drought in Great Plains Optimal SST Forcing for Drought in US With FeedbackWithout Feedback

18. What Have We Learned? Important Role of SST in Droughts and Pluvials World-Wide –Dominant role of tropical Pacific SST –Important role of the tropical Atlantic/IAS –Important role of land-atmosphere feedbacks –Strong seasonality of responses (seasonally-changing impacts of planetary waves, jetstream dynamics/large-scale subsidence, weather, low level circulations/LLJs, land-atmosphere feedbacks, predictability) –General agreement among models on global response, but substantial differences on regional scales Over the US –Models agree that: Cold Pacific+Warm Atlantic => drought/warm Warm Pacific+Cold Atlantic => pluvial conditions/cold –The models disagree on the regional details: Sensitivity to errors in stationary waves Sensitivity to strength of land-atmosphere coupling Sensitivity to low level response in the IAS/Caribbean

19. Future Directions Much more to study in current idealized and AMIP-style runs –Physical mechanisms linking SST, Impact of land –Other parts of the world (focus was on response over North America) –ftp://gmaoftp.gsfc.nasa.gov/pub/data/clivar_drought_wg/ftp://gmaoftp.gsfc.nasa.gov/pub/data/clivar_drought_wg/ Continue Focus on: –Dependence on Time scales: Seasonal, Inter-annual, Decadal/Climate Change –AGCM: response to SST, stationary waves, warm season precipitation, roles of different ocean basins including IAS, land-atmosphere coupling strength –Coupled model issues: realistic SST variability, +AGCM issues –Resolution issues: e.g. diurnal cycle, mesoscale, LLJ, role of weather –Role of land: soil moisture, vegetation, aerosols –Observations: soil moisture monitoring and ICs: role of LDAS, satellite measurements, improved information/inferences about coupling strength –Other quantities (snow, run-off, temperature, etc) Programs/related activities –Drought interest group (CLIVAR/GEWEX) –VAMOS panel on extremes, IASCLIP – AR5 IPCC runs including decadal simulations