climate change and rainfall variability

8/14/2019 Climate Change and Rainfall Variability

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Climate ChangeClimate Change

Dr. Azra AzadDr. Azra Azad


2/35

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


4/35

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


5/35

Sala et al. 1988

Grasslands (most) are water limited systemsRainfall vs. Production across the Central US

Setting the stage


6/35

The world is getting warmer. (thermometer evidence)


7/35

Dave Theobald

Plant evidence


8/35


9/35

Dave Theobald


10/35Overpeck et al. 2003

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


11/35

Rainfall regimes

CO2 effects

Temperature effects

Soil moisture

Plant water relations

+

+ -

-

Water, temperature (and CO2) are linked in

grasslands and most ecosystems


12/35

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.


13/35


14/35

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.jpg


15/35

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


16/35

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


17/35

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?


18/35

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


19/35

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%


20/35

All rainfall treatments

Wh t b t th Sh t t & i id d id


21/35

What about the Shortgrass steppe & semi-arid and arid

grasslands?

Like all grasslands, a

system of extremes

2005 Sh t t


22/35

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



9 eventsCV = 1.12

CV = 0.46

CV = 0.37

CV = 0.09

Dry Interval = 10 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


23/35

# 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


24/35

Ojima and

Lackett 2002Ojima and

Lackett 2002

Tall-grass

Mid-grass

Short-grass

Precipitation

gradient

Regional perspective

500 KPBS


25/35

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


Long dry intervals

Increases ANPP?

With the same experimental

design, how will these different

grasslands respond?

Mesic grassland


Long dry intervals

Reduces ANPP?

Experimental alteration of rainfall patterns


26/35

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


27/35

Mesic GrasslandKNZ 2006

# of 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


28/35

Semi-arid Grassland

# of rain 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
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29/35

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
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30/35

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


31/35

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


32/35

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?


34/35

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

climate change and rainfall variability

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