reconstructing past droughts in texascentral texas drought history (cleaveland et al., 2011)...
TRANSCRIPT
![Page 1: Reconstructing Past Droughts in TexasCentral Texas drought history (Cleaveland et al., 2011) Calibrate tree rings to instrumental PDSI record Measure tree rings to reconstruct PDSI](https://reader034.vdocuments.net/reader034/viewer/2022051807/60077960cf04f123842f7037/html5/thumbnails/1.jpg)
Richard Casteel Jay Banner
Jackson School of Geosciences Environmental Science Institute
LCRA; http://www.lcra.org/water/save/drought_plans.html
Reconstructing Past Droughts in Texas
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Outline
• Texas climate
– Present and past droughts
• Drought reconstructions:
– Tree rings
• Hot vs. dry droughts
• Temperature reconstructions:
– Stalagmites
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PDSI
1. Temperature 2. Rainfall 3. Soil moisture
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Tree rings High resolution: Annual PDSI
reconstruction
PDSI reconstruction of the last 500 years
http://www.duetsblog.com/2
012/07/articles/t
http://www.futurity.org/earth-environment/fragile-forests-hard-hit-by-warming/
How severe and protracted were past droughts?
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(Cleaveland et al., 2011)
Climate regions of Texas
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Bald Cypress
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Biggest tree in Texas
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Tree core
extraction
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Bald cypress tree core
1 mm
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Central Texas drought history
(Cleaveland et al., 2011)
Calibrate tree rings to
instrumental PDSI
record
Measure tree rings to
reconstruct PDSI
Severe drought
At least once a century
since 1500s
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Triggers and sustaining mechanisms of drought in SW US
Two types in the SW US:
1. Dry droughts Triggered/sustained by lack of rainfall
2. Hot droughts Triggered/sustained by high temperatures
(Weiss et al., 2009)
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Hot vs. dry drought
DRY DROUGHT HOT DROUGHT
EXAMPLE 1950s 2000s
RAINFALL LOWER (74%) HIGHER (86%)
TEMPERATURES COOLER WARMER (+1o C)
PDSI LESS NEGATIVE LESS DRY THAN 2000s
MORE NEGATIVE DRIER THAN 1950s
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Tree rings as drought proxies
• Reconstruct PDSI
– Temperature
– Rainfall
– Soil moisture
• One component temperature
• Two components moisture
• How to separate hot vs. dry droughts?
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Stalagmites Oxygen isotopes (δ18O) as a temperature proxy
http://www.encyclopedia.com/topic/stalactite_and_stalagmite.aspx http://www.stonemania.co.uk/glossary/244-stalagmites
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Westcave Preserve
Westcave Preserve
Austin
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Westcave: Outside
http://www.nomadicpursuits.com/blog/2010/6/2/westcave-preserve.html
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Westcave: Inside
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Cave drip waters
Surface water infiltrates into cave
Drip waters precipitate calcite and make stalagmites
Place glass plates for drip waters to precipitate calcite on
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Calcite collection plates
Analyze oxygen
isotopes of
plate calcite
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WC-3 plate calcite oxygen isotopes
-6
-5
-4
-3
Date1/1/20051/1/20061/1/20071/1/20081/1/20091/1/20101/1/20111/1/2012
Tem
pera
ture
(oC
)
0
10
20
30
Calc
ite o
xyg
en
iso
top
es
Temperature33.1 oC31.5 oC 32.3 oC
30.8 oC 29.4 oC 31.4 oC29.8 oC
Temperature vs. plate calcite
oxygen isotopes
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older
younger
Oxygen
isotopes of
the stalagmite
Reconstruct
temperature
Stalagmite
WC-3
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WC-3 stalagmite oxygen isotopes WC-3 plate calcite oxygen isotopes
-6
-5
-4
-3
Date1/1/20051/1/20061/1/20071/1/20081/1/20091/1/20101/1/20111/1/2012
Tem
pera
ture
(oC
)
0
10
20
30
Calc
ite o
xyg
en
iso
top
es
Temperature33.1 oC31.5 oC 32.3 oC
30.8 oC 29.4 oC 31.4 oC29.8 oC
Temperature vs. stalagmite
oxygen isotopes
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Climate proxies
• PDSI (tree rings)
– Temperature
– Soil moisture
– Rainfall
• Oxygen isotopes (stalagmites)
– Temperature
Dry droughts vs. hot droughts
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Conclusions
• Droughts in the past were at least as severe and/or more protracted than the drought of record
• Increased temperatures can trigger/sustain droughts
• Possibility of teasing apart temperature from PDSI
– Occurrence of dry droughts or hot droughts
• Potential of stalagmites as temperature proxies
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Acknowledgements
• Malcolm Cleaveland, University of Arkansas
• Guadalupe-Blanco River Authority and Todd Votteler
• Jackson School of Geosciences
• Environmental Science Institute
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Conclusions
• Higher temperatures predicted
• Tease apart hot vs. dry droughts using:
– Reconstructed PDSI (tree rings)
– Reconstructed temperature (oxygen isotopes)
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Variables that can effect stalagmite geochemistry
• Rainfall
• Temperature
• How to tell the difference?
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What are the droughts triggers
We only have 2 data points, the 1950s and 2000s.
So.....
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• We also place plates at drip sites to collect calcite
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“Past is the key to the future”
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• Speleothem sample
• U-series dating for age
constraints
• Geochemically analyze
samples taken along
the growth axis
• Reconstruct climate
younger
older
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Future climate projection:
Increased temperature
Rainfall distribution uncertain
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24,000 years ago
Low latitude ice
sheets (~39° N)
Cooler and wetter
-Faunal evidence
-Pollen data