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Climate ChangeClimate Change
Dr. Azra AzadDr. Azra Azad
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Why should we care about climate
change?
We may be witnessing one of the most profound climaticchanges in the Earth's history.
Predictions for the 21st century show warming of the troposphereespecially in the Arctic, an increase in precipitation extremes, adecrease in snow and ice cover, and an increase in sea level.
The danger facing society today is that anthropogenic globalwarming may be too fast to allow humans, and other species, toadapt to its detrimental impacts.
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T. Riley and J.A. Klein
Grasslands, rangelands, steppe, tundra, savanna and shrub-
grasslands cover ~ 40% of the Earths land surface
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Ecosystem Services Grasslands Provide:Ecosystem Services Grasslands Provide:
Forage for domestic livestockForage for domestic livestock Habitat for native ungulatesHabitat for native ungulates
Habitat for grassland plants/animalsHabitat for grassland plants/animals Migratory birds breeding/forageMigratory birds breeding/forage
Soil erosion controlSoil erosion control Carbon se uestrationCarbon sequestration
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Sala et al. 1988
Grasslands (most) are water limited systemsRainfall vs. Production across the Central US
Setting the stage
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The world is getting warmer. (thermometer evidence)
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Dave Theobald
Plant evidence
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Dave Theobald
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History provides few analogs for the type of climate
change forecastwe are in uncharted waters
Little Ice Age:
1600-1700s -bitter winters,famine inEurope
Younger Dryas 1300 yr coldperiod (11,000 BP), then rapidwarming
IPCC predictions
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Rainfall regimes
CO2 effects
Temperature effects
Soil moisture
Plant water relations
+
+ -
-
Water, temperature (and CO2) are linked in
grasslands and most ecosystems
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Global Climate Model (GCM) predictions for changes in
mean annual rainfall changes are inconsistent with each
other in magnitude and signBut more extreme weather as
the atmosphere warms is consistently predicted.
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Dust Bowl of 1930s in USDust Bowl of 1930s in US
Drought in SenegalDrought in SenegalMore
intensehurricanes
and floods
Are grasslandsvulnerable to this
aspect of climate
change?
Focus on subtle increases in extreme events or shifts in
rainfall patternsnot the obviousbut the pervasive
Proportion of total rainfall in the US from large (>5 cm) rainfall events
Prop
ortion(%)ofrainfallinex
tremeevents
http://en.wikipedia.org/wiki/Image:Hurricane_Katrina_August_28_2005_NASA.jpghttp://en.wikipedia.org/wiki/Image:Hurricane_Katrina_August_28_2005_NASA.jpg8/14/2019 Climate Change and Rainfall Variability
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Goldewijk
and
Battjes(19
97)
Reid
&Mil le
r
(198
9)
Vitousek (1994)
NOAA
Ecological
Systems
Climate Change
is but one facet of
Global Change
Grazing
J.A. Klein
Okl h
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Proportion of total rainfall in the US from large (>5cm) rainfall events
Proportion(%)
ofrainfallin
extremee
vents
Rainfall variability/
Abundant evidence thatrainfall regimes are changing
Oklahoma
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12 rainfall manipulation plots
Collect, store, and reapplynatural rainfall on intactgrassland plots
12 rainfall manipulation plots
Collect, store, and reapplynatural rainfall on intactgrassland plots
The Rainfall ManipulationPlot (RaMP) Experiment
Address the impact ofchanges in size andtimingofgrowing season rainfall
To what extent willaltered rainfall patternsaffect ecologicalprocesses in grasslands?
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Experimental manipulation: 50% longerinter-rainfall periods, larger individual rain events
No change intotal
precipitationquantity
Current
Predicted
Pre
cipitationamount
Day of yearFewer events
Greater storm size
Increased dry periods
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Ambient ppt timing:
typical seasonalpattern
Altered ppt timing: repeated deficits more extreme wetting
and drying cycles
Ambient ppt timing:
typical seasonalpattern
Altered ppt timing: repeated deficits more extreme wetting
and drying cycles
Key driver of responses: Soil moisture dynamicsKey driver of responses: Soil moisture dynamics
Average soil water
content in top 30 cm:
- reduced by 12%
Variability in soil
moisture:
- increased by 27%
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All rainfall treatments
Wh t b t th Sh t t & i id d id
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What about the Shortgrass steppe & semi-arid and arid
grasslands?
Like all grasslands, a
system of extremes
2005 Sh t t
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10
20
30
40
50
60
70
Precipitation(mm)
10
20
30
40
50
60
70
10
20
30
40
50
60
70
Day of year
150 180 210 240 270
10
20
30
40
50
60
70
12 events
6 events
4 events
AMBIENT Mean Event = 21.1 mm
Mean event = 15.8 mm
Mean event = 31.7 mm
Mean event = 47.5 mm
9 eventsCV = 1.12
CV = 0.46
CV = 0.37
CV = 0.09
Dry Interval = 10 days
Dry Interval = 13 days
Dry Interval = 20 days
Dry Interval = 30 days
Frequent small events (10
day intervals, 15 mm events)
Infrequent big events (30 day
intervals, 47 mm events)
All received average MAP
amounts
2005 - Shortgrass steppe
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# of rainfall events
Ambient 12 events 6 events 4 events
ANPP(g
/m2)
0
50
100
150
200
250
a
b
c c
long-term meanANPP
97 g/m2
(9 events)
- Heisler et al. 2008
Semi-arid grassland
Extreme rainfall events
Long dry intervals
Increases ANPP
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Ojima and
Lackett 2002Ojima and
Lackett 2002
Tall-grass
Mid-grass
Short-grass
Precipitation
gradient
Regional perspective
500 KPBS
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Annual Precipitation (mm)
358 578 833
A
NPP(g/m2)
0
100
200
300
400
500
SGSshortgrass steppe, CO
HAYSmixed grass prairie, KS
KPBStallgrass prairie, KS
Semi-arid grassland
Extreme rainfall events
Long dry intervals
Increases ANPP?
With the same experimental
design, how will these different
grasslands respond?
Mesic grassland
Extreme rainfall events
Long dry intervals
Reduces ANPP?
Experimental alteration of rainfall patterns
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SGS
Experimental alteration of rainfall patternsacross the Great Plains of North America
Frequent, small events
Fewer, infrequent largeeventsVS.
A = 12 eventsB = 6 events
C = 4 eventsTotal = 191 mm
A = 12 eventsB = 6 events
C = 4 eventsTotal = 450 mm
KNZ
Semi-arid Mesic
Jana Heisler
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Mesic GrasslandKNZ 2006
# of events
Ambient 12 events 6 events 4 events
Producti
on(g/m2)
100
200
300
400
500
600
700a
b
cc
A shift from 12to 4 eventsresults in a 15%decrease inproductivity.
More extremerainfall regime
Shift to more extreme (large) rainfall events reducedproductivity
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Semi-arid Grassland
# of rain events
Ambient 12 events 6 events 4 events
Production
(g/m2)
20
40
60
80
100
120
140
a
a
bb
A shift from 12 to4 events resultedin a 30% increase
in productivity.
More extremerainfall regime
Shift to more extreme (large) rainfall events increased
productivity
http://sev.lternet.edu/modules.php?full=1&set_albumName=album96&id=Places_East_Side_Land_and_Sky_Tom_Miller&op=modload&name=gallery&file=index&include=view_photo.php8/14/2019 Climate Change and Rainfall Variability
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Sevilleta LTER Central New Mexico
Monsoon rainfall addition experiment: 20 mm events vs. four 5
mm events
S ll d il t t t l t t t t h t th i
http://sev.lternet.edu/modules.php?full=1&set_albumName=album96&id=Places_East_Side_Land_and_Sky_Tom_Miller&op=modload&name=gallery&file=index&include=view_photo.phphttp://sev.lternet.edu/modules.php?full=1&set_albumName=album96&id=Places_East_Side_Land_and_Sky_Tom_Miller&op=modload&name=gallery&file=index&include=view_photo.phphttp://sev.lternet.edu/modules.php?full=1&set_albumName=album96&id=Places_East_Side_Land_and_Sky_Tom_Miller&op=modload&name=gallery&file=index&include=view_photo.phphttp://sev.lternet.edu/modules.php?full=1&set_albumName=album96&id=Places_East_Side_Land_and_Sky_Tom_Miller&op=modload&name=gallery&file=index&include=view_photo.php8/14/2019 Climate Change and Rainfall Variability
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Seasonally averaged soil water content, plant water status, photosynthesis,
and production were highest in plots receiving a small number of large events
Collins, Thomey, Johnson, Brown,
Natvig, Friggens
20 mm
events
5 mm
events
20 mm
events
5 mm
events
Wh d d i l d d
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Why do dry vs. mesic grasslands respond
differently?
Two aspects of more extreme rainfall regimes:
1. Larger rain events
2. Longer dry periods between events
When soils are usually moist, longer dry periods are
most important
When soil are already dry, larger rain events cause
the greater response
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0
25
50
75
Day of Year
120 140 160 180 200 220 240 260
-75
-50
-25
0
SoilWaterContent(%change
)
Mesic (wet) Grassland
0
25
50
75
100
Day of year
140 160 180 200 220 240 260
-100
-75
-50-25
0
Semi-arid (dry) Grassland
Wet relative to ambient
Dry relative to ambient
Responses to climate change depends on location even in
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Sala et al. 1988
Responses to climate change depends on location even inthe same grassland biome this make generalizations achallenge
Predictionbased onwet
grasslandresponses
Predictionbased on drygrasslandresponses
The future?
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we are changing Earth more rapidly than we are
understanding it.
-Vitousek et al. 1997
We have moved beyond
questions such as Is
climate change
happening? There is
little uncertainty about
this.
The uncertainty is withthe consequences of
climate change
Key Points:
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Key Points:
Research indicates that subtle climate change can have surprising
consequences.
1. Even subtle changes toward more extreme rainfall patterns can alter
production and the sensitivity of the grasslands to changes in rainfall
amounts
2. Grasslands can respond in opposing ways to the same form of climate
change