The Perfect Ocean for Drought, Martin Hoerling & Arun Kumar On the Cause of the 1930s Dust Bowl, Siegfried D. Schubert, Max J. Suarez, Philip J. Pegion, et al. CAITLIN STRIPLING THE OHIO STATE UNIVERSITY ATMOSPHERIC SCIENCE GRADUATE STUDENT (MS)

Overview  Introduction  Hoerling  Data & Methods  Results  Summary  Schubert  Data & Methods  Results  Summary  Conclusion

Introduction  Drought: an extended period when a region receives a deficiency in its water supply, whether atmospheric, surface or ground water.  Regions most affected:  Western U.S.  Eastern Australia  Equatorial/South Africa  South America (Brazil)  Asian Regions (China and India)

Introduction  Global impacts  Mitigation and relief efforts: Cloud Seeding Desalination (Sorek; Israel) Rainwater harvesting (MITHE, Mexico City) Dams (Jawa Dam remains, Jordan)

Hoerling’s Study How were the droughts spanning the U.S., southern Europe, and southwest Asia connected?

Data Collection Methods  Atmospheric General Circulation Models (AGCMs)  ECHAM4.5  NCEP  NSIPP

Observed Conditions Observed temperature and precipitation conditions from Above normal temperatures No more than 50% of rainfall, annually. Decreased rainfall  Increased land temp  Drought conditions

Observed Conditions (cont.) Observed sea surface temperatures (SSTs). La Niña Conditions: Warm pool in tropical Indian and west Pacific. Cold tongue in equatorial central/east Pacific. Uninterrupted warmth in warm pool. Cold tongue peaked in early winter and weakened in late spring.

Modeled Temperature and Precipitation Combined results of three GCM models. Drying over U.S., southern Europe, and southwest/central Asia. Higher land temperatures, lower precipitation amounts. Drying was strongly ocean driven (easily reproduced).

Modeled Pressure Observed vs. modeled 200mb heights. Uninterrupted high pressure in mid- latitudes. Symmetry of atmospheric anomalies about equator.

Modeled Tropical SSTs Testing tropical SSTs impact on droughts. Three tests: All Tropical Warm Tropical Only Cold Tropical Only The use of all tropical SSTs yielded the closest results to what was actually observed.

Summary of Results  Widespread mid-latitude drought strongly determined by tropical oceans.  Ocean conditions “perfect” for severe, sustained drought in mid-latitudes.  SST anomalies due to increase GHGs, rather than natural variability in ENSO.

Schubert’s Study Since the 1930s experienced weak Pacific SST anomalies, what prompted the generation of the Dust Bowl?

Data Collection Methods  Similar methods  AGCMs  NSIPP modeling  100-year runs, Climate of the 20 th Century project (C20C)  Modeling ocean basins separately

Preliminary Data/Models Observed vs. modeled precipitation of 20 th Century. Similarities– dry tendency in 1930s, abrupt transition to wet conditions. Inability to model conditions in northern plains, Canada, and Mexico correctly. Sea surface temperatures based on collected data from ships. Best estimate.

Experiment Time! Tested subregions of the three tropical basins to see how their SSTs influenced the rainfall and drought conditions.

Global vs. Tropical Modeling C20C mean vs. global, tropical, global minus tropical models. Global model very similar to C20C, with additional deficit in Alabama and surplus in northwest U.S. Tropical decreased affected area. Global minus tropical broadened area.

Global Modeling: With/without Atmosphere-Land Interactions Global run without land- atmosphere interactions. Reduced deficit by 50%. Land-atmosphere interactions highly responsible for drought severity.

Seasonal Distribution of Rainfall Seasonal averages. Global and fixed beta model underestimate deficits. For the fixed beta: Winter: Slight surplus. Spring: Small deficit. Summer: Slightly larger deficit than spring. Fall: Largest deficit. Look to summer and fall for SST anomalies affecting Dust Bowl region.

Summary of Results  Cause still unclear  Additional proof that tropical Pacific and Atlantic SSTs impacted precipitation variations. SSTs + Rainfall Deficit + Land-Atmosphere Interactions = Drought Conditions

Conclusion  Limited availability of data  Current/future projects  Drought relief

References  The Perfect Ocean for Drought, Martin Hoerling & Arun Kumar  On the Cause of the 1930s Dust Bowl, Siegfried D. Schubert, Max J. Suarez, Philip J. Pegion, et al.   out-several-regions-sparking-food-production-concerns  gascale-desalination/  project/  