4/9/14
Great Plains Droughts and Megadroughts in Prehistory
Sheri Fritz, Department of Earth and Atmospheric Sciences, Robert B. Daugherty Water for Food Institute University of Nebraska - Lincoln G. Steinmetz, National Geographic 2002
What can we learn from studying the past? § Patterns of natural drought variation § Magnitude § Duration § Spatial extent § Response of landscape and biota to droughts of differing character
Arthur Rothstein
1 4/9/14
2012 Drought (“Pan-continental”) Synchronous drought in multiple regions
Epic North American Droughts
Cook et al.
2 4/9/14
Tree-ring Reconstructions
Stahle 2003
Climate of the late Holocene (last ~4000 yr) Climate system in ~ same configuration as today
Ruddiman 2008
3 4/9/14
Major and Prolonged Drought Medieval “Mega-droughts”
Medieval Period
Dust Bowl
Moon Lake, south-central North Dakota Laird, Fritz et al. 1996
Tree-ring Reconstructions Central Plains Palmer Drought Severity Index
Wet
Dry
Date (AD)
Medieval
Cook et al. 2014
4 4/9/14
Tree-ring Reconstructions Medieval “Mega-droughts” Pan-continental drought
Saeger et al. 2009
Late-Holocene “Mega-droughts”
Medieval Roman 16th c
Moon Lake, south-central North Dakota
Laird, Fritz et al. 1996
5 4/9/14
Holocene Drought Variability
Roman Medieval mid-Holocene
Kettle Lake, northwestern North Dakota
Hobbs, Fritz et al. 2011
The Nebraska Sand Hills
Map from J. Swinehart and D. Loope
6 4/9/14
Nebraska Sand Hills Dunes Record Medieval Drought
Photo by David Loope
Jumbo Fen, Nebraska Sand Hills
Nicholson and Swinehart 2005
7 4/9/14
Dunes Advance over Valleys during Major Drought
Nicholson and Swinehart 2005
Altered Mean Wind Direction in Medieval Times
Contemporary Medieval Wind Direction Wind Direction
V Sridhar et al. Science 2006;313:345-347
Published by AAAS
8 4/9/14
Oceanic Forcing of North American Drought
Southern Oscillation (ENSO)
Pacific Decadal Oscillation
Atlantic Multi-Decadal Oscillation
Cook et al. 2014
Dust and Vegetation Loss Amplify Drought Persistence
Pacific SST only
SST plus veg loss
SST plus veg loss plus dust
Cook et al. 2013
9 4/9/14
Aa Dune and Loess Record of Paleoclimate
Episodes of aeolian activity, based on loess record
mid- Optical ages Holocene ± σ (with 2 errors) Loess Aeolian Sand
0 5000 10000 15000 20000 25000 Years Ago Miao et al, 2007
Enhanced Fire during Wet Intervals Beaver Lake, Cherry County, Nebraska
Grasses
-type -type
Iva xanthifolia MyriophyllumTypha latifolia Artemisia Ambrosia Isoëtes PotamogetonSagittaria Charcoal concentrationChenopodiaceae/AmaranthaceaePoaceae Pinus 0 500 1000 1500 2000 2500 3000 3500 4000
Age (calendar years (calendar Age BP) 4500 5000 5500 6000 20 40 60 80 20 40 60 20 40 60 20 20 20
Schmieder, Fritz, Grimm et al. 2013
10 4/9/14
Early 20th century “pluvial”
Laws regulating stream flow were established in early 1900s in many parts of western US Cook et al. 2011
Insights from the Long-term Record
• Droughts equivalent in magnitude to the most severe 20th century droughts have been recurrent every century, including pan-continental drought • In many regions of western North America, pre-20th century droughts have lasted a decade or more - thus drought has been more persistent than in the 20th century • In many parts of western NA, the early 20th century was unusually wet (pluvial) • Paleo data provide useful targets for model exploration of the conditions that produce severe and persistent drought
11 4/9/14
1:30 – 3:00 PM Today: Drought: A Prehistoric Perspective: Paul Hanson, Rolfe Mandel, Connie Woodhouse
G. Steinmetz, National Geographic 2002
12