Global Change and Agriculture: The Effects that Plants Have on Climate, and Vice Versa

Dennis BaldocchiProfessor of Biometeorology

Department of Environmental Science, Policy and Management

College of Natural Resources

State Board of Food and AgricultureJuly 25, 2007

Topics Covered

• Trends in Temperature– Implications on Winter Chill/Dormancy

• Trends in Phenology– +/- of Increasing Growing Season Length

• Trends in Water Use – Pan ET and ‘Solar Dimming’

– Combined effects of Elevated CO2 and Temperature

• Trends in Land Use Change– Evaporative Cooling and Albedo change

Summary

• Climate Change is in Motion in California– CA is warming, but interannual variation in rainfall is greater than predicted trends in the

near term• There is a trend in reduced winter chill and winter dormancy

– Leads to a reduction in fruit and nut production– The future trends may not be linear, but could accelerate if winter fog patterns change– Breeding programs are needed to produce cultivars that require less winter chill

• Spring phenology is advancing– Increase vulnerability of fruit trees to late frost– May increase carbon sequestration, if water is plentiful, and increase water use– may cause a miss-match between flowering and pollinators

• Water consumption will increase in the future– Potential water ‘savings’ by elevated CO2 are offset by warmer temperatures– CA is not be experiencing water savings due to ‘solar dimming’.

• Land use change from Natural to Agricultural Landscapes has altered the surface energy balance

– Crops are Darker than grasslands and absorb more energy– But Evaporative cooling reduces air temperature, in comparison

Temperature and Agriculture

• Length of Growing Season

• Length of Dormant Season

• Extreme Cold– Fruit, flower, and/or pollination damage

• Extreme heat– Fruit damage– Leaf damage

1940 1950 1960 1970 1980 1990 2000 2010

Me

an

te

mp

era

ture

(oC

)

14.5

15.0

15.5

16.0

16.5

17.0

17.5

18.0

Camp Pardee, CAFoothill Rangeland

Year

1950 1960 1970 1980 1990 2000 2010

Ta

ir(C

)

14

15

16

17

18

19

Antioch, CASac-San Joaquin Delta

Temperature Trends, Selected Sites

Warming Rate: ~ 1.5 C ++ per 50 Years

Tmin

Tmax

Tref

a

d

b

c

TaveNoon

chillhours d TT T

refref

2

2( )min

dchillhours

T Tref 2

tan ( )min tanmin

a

b

hr

T Tave

6

Estimating Winter Chill

Year

1985 1990 1995 2000 2005 2010Ch

ill D

eg

ree

-Ho

urs

, be

low

7.2

2 o

C N

ov1

thro

ug

h F

eb

29

1000

1500

2000

2500

3000

3500

4000

Brentwood, CA

Year

1985 1990 1995 2000 2005 2010

Ch

ill H

ou

rs, b

elo

w 7

.22

oC

No

v1 th

rou

gh

Fe

b 2

9

400

600

800

1000

1200

1400

1600

Downward Trend in Chill Hours near Brentwood, East Contra Costa

20 year record, CIMIS Data

-124 -123 -122 -121 -120 -119 -118 -117 -116 -115

33

34

35

36

37

38

39

40

41

42

-100 to -75 -75 to -50 -50 to -25 -25 to -10 -10 to 0 0 to 10

Trends in W inter C hill D egree H ours Accum ulation (degree-hours per year)N ov-M ar, 0 to 7.22 C

Baldocchi and Wong, Climatic Change, in press

Red Bluff, CA, B1

Years

1940 1960 1980 2000 2020 2040 2060 2080 2100 2120

Ch

ill H

ou

rs,

be

low

7.2

2

o C

200

400

600

800

1000

1200

1400

1600

Davis, CA, B1

Years

1940 1960 1980 2000 2020 2040 2060 2080 2100 2120

Ch

ill H

ou

rs,

be

low

7.2

2

o C

0

200

400

600

800

1000

1200

1400

1600

1800

Fresno, CA, B1

Years

1940 1960 1980 2000 2020 2040 2060 2080 2100 2120

Chill H

ours, belo

w 7

.22

o C

200

400

600

800

1000

1200

1400

1600

Reductions in Winter Chill are being Experienced across the State and they are expected to Continue into the Future

Alm

ond Y

ield

(to

n a

cre

-1)

Alm

ond Y

ield

Anom

aly

D. Lobell et al, 2006 Ag.Forest Met

 Photo © David Sanger

So What?:

Almond Yield Decreases with Warmer and Wetter winters

Phenology: The Timing of Plant Activities

Flowering Leaf-out

Schwartz et al. 2006 Global Change Biology

Spring is Advancing by about 3 days per Decade across the Northern Hemisphere

Estimated Trends in Phenology in CA Rangeland

Estimate of onset of photosynthesis for blue oak woodland

Year

1940 1950 1960 1970 1980 1990 2000 2010

Day

NE

E =

0

82

84

86

88

90

92

94

96

98Coefficients:b[0] 303.01b[1] -0.108r ² 0.331

Length of Growing Season, Carbon and Water Exchange

Broad-Leaved Forests

Length of Growing Season

100 150 200 250

NE

E (

gC

m-2 y

r-1)

-800

-700

-600

-500

-400

-300

-200

-100

0

100Japan

Denmark

Italy

Massachusetts, USA

Belgium

Tennessee, USA

Prince Albert, CANADA

Ontario

Indiana, USA

Michigan, USA

Baldocchi et al, 2001 Bull. Am. Meteorol. Soc.Ryu, Baldocchi and Ma, unpublished

Annual Grassland, CA

Deciduous Forests

Antioch, CA

Year

1950 1960 1970 1980 1990 2000 2010

rain

fall

(in

ches

per

yea

r)

0

5

10

15

20

25

30

Camp Pardee

Year

1940 1950 1960 1970 1980 1990 2000 2010

annu

al P

reci

p (

mm

)

0

200

400

600

800

1000

1200

mean: 548.6446stddev: 196.2281

Water and Agriculture

•Year to Year Variability Exceeds any Existing or Expected Future Trends

•Snowpack and the Timing of its Melting will be Affected

Evaporation, Water Availability and Climate Change

• Global Warming Should: – Accelerates the Water Cycle by increasing

saturation vapor pressure– Increase Evaporation

• But Negative Feedbacks include:– Increase Humidity and Cloud Cover– Decrease Solar Radiation, ‘Solar Dimming’– Widespread Reduction in Pan or Potential

Evaporation

Liu et al. Journal Geophysical Research, 2004

Pan ET in China

Literature is showing a long term trend with a decrease in pan evaporation:

Could there be Water Savings for Irrigated Agriculture in CA?

Solar Radiation in China

Trends in Pan Evaporation in CA:

Irrigated Central ValleySemi-Arid Rangeland

Hildalgo et al. 2005 J Hydromet:‘Trends for PET are unclear in CA’

Davis, CA

Year

1940 1950 1960 1970 1980 1990 2000 2010

Pan

ET

(in

yea

r-1)

50

60

70

80

90

100

110 Camp Pardee

Time

1945 1950 1955 1960 1965 1970 1975 1980

Pan

ET

(in

y-1

)

48

50

52

54

56

58

60

62

64

66

68

Antioch, CA

Time

1955 1960 1965 1970 1975 1980

Pan

ET

(in

y-1

)

60

62

64

66

68

70

72

74

76

78

P/Epot

Ea/Epot

0

1

Water limited Energy limited

Ea/Epot

Q/Epot

0 1P/Epot

Ea/Epot

0

1

Water limited Energy limited

Ea/Epot

Q/Epot

0 1P/Epot

Ea/Epot

0

1

Water limited Energy limited

Ea/Epot

Q/Epot

0 1

Farquhar and Roderick, Pontifical Academy of Science, in press

•Feedback Loops Break in Water-Limited Regions

Savanna Woodland and Annual Grassland

<Rg> (MJ m-2 d-1)

17.4 17.6 17.8 18.0 18.2 18.4

ET

(m

m y

-1)

240

260

280

300

320

340

360

380

400

420

440

Lessons from Direct Evaporation Measurements over California Rangeland

•CA Ecosystem are Water, not Radiation Limited•Savanna Uses More Water than Grassland

-Savanna Soil holds about 78 mm more Water•Annual ET Decreases with Solar Radiation

-Rg decreases as Clouds and Rain increase-Range in ET is 100 mm/yr

Ryu, Ma and Baldocchi, unpublished

• Enhances Photosynthesis– Down-Regulation in Ps from

Nutrient Limitations• Reduces Stomatal Closure

– Direct Effect• Reduces Transpiration and

Increases WUE– InDirect Effect and Positive

Feedback• Elevated Leaf Temperature,

augments Transpiration

• Greater Growth and Leaf Area– Bigger plants grow faster. +– Bigger plants transpire more– Soil moisture pool depleted

faster: -• Herbivore Interactions

– Insects eat more foliage to compensate for lower N quality of leaves

Elevated CO2, Facts and Myths

Walnuts2003 Climate data

Day

0 50 100 150 200 250 300 350 400

LE (

W m

-2)

0

50

100

150

200

250

ET: 1054 mm

Day

0 50 100 150 200 250 300 350 400

LE

(W

m-2

)

-20

0

20

40Ta + 3C, CO2 =500 ppm

ET: 1199 mm

Projected Water Use in a Walnut Orchard will increase by ~145 mm (6 in) with T+3 C and CO2 at 500 ppm

Agriculture and Land use Change

• Albedo– Crops are darker than dead grass,

so the Absorb more solar energy• Evaporation Ratio, E/Rn

– Crops do not suffer for soil moisture deficits and are fertilized

– They achieve a larger Leaf Area Index and possess lower Surface Resistance than annual grasses or savanna woodlands

– Crops experience greater rates of ET and have depressed Surface Temperatures, compared to native vegetation

• Carbon Uptake– Crops are actively assimilating

carbon dioxide during the summer

PBL:1500 m

PBL:1000 m

S = 0.08 Rn

G = 0.02 Rn

H = 0.3 Rn

LE = 0.6 Rn

= 0.15 Rg

Rn = 0.65 Rg

LEn = 0.8 Rn

= 0.25 Rg

H = 0.05 Rn

Rn = 0.85 Rg

S = 0.15 Rn

Rcanopy (s m-1)

10 100 1000 10000

E/

Eeq

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

wheatcornjack pineoak-savanna

Land Use Change and Climate Change in the Central Valley

Kueppers et al, 2007, Geophysical Res. Letters

Christy et al, 2004, J Climate

•Large Scale Irrigation reduces Temperature compared to natural vegetation

•But Increases Nighttime Temperatures through humidification of the air and increasing downward longwave energy

•Rate of Climate Warming in CA is dampened due to Land Cse Change

-negative feedbacks by evaporative cooling outpace positive effects of lower albedo

Difference in Tmax: Natural vs managed land

Some Potential Solutions

• Changes in crops, timing and rotation– Don’t grow crops that are profligate water

users in the desert!

• Irrigation scheduling and soil moisture management

• Mulches and increased soil organic matter to reduce soil evaporation and runoff

• Precision agriculture and drip irrigation

We are Linked to Past, We have a Responsibility to the Future

Palace of Minos at Knossos, ~2000 BC

•Climate Change is in Motion in California

•Long term production of valuable fruit crops is vulnerable due to trends in reduced winter chill

•The future trends may not be linear, but could accelerate if winter fog patterns change

•Breeding programs are needed to produce cultivars that require less winter chill

•Water consumption will increase in the future

Extra Background Material

Temperature Anomaly Trends:Instrument Record

Mote et al. 2005 BAMS

Trends for Climate between Nov and Mar

McKinney et al,2006 AgForMet

Lobell et al 2006 AgForMet

Lobell et al 2006 AgForMet

Critical Temperatures and Yield

Menzel et al 2006 GCB; Menzel and Fabian, Nature, 1999

Regression Coefficient of Phenological Event with Time, days per year

Phenology, a Measure of Global Change

Feng and Hu, 2004, J Theor Appl Clim

Trends, days per Decade

Feng and Hu, 2004, J Theor Appl Clim

Trends in Growing Season Length and Last Frost Dat

United States

Christy et al 2006 J Climate

Feng and Hu, 2004, J Theor Appl ClimUnited States

Trends in Dry and Wet Spells

Coupled Energy Balance-PBL ModelD. Baldocchi, unpublishedDoes Global Dimming affect ET?

Rg (MJ m-2 d-1)

28.5 29.0 29.5 30.0 30.5 31.0 31.5 32.0 32.5

ET

(m

m d

-1)

5.3

5.4

5.5

5.6

5.7

5.8

5.9

6.0

6.1

b[0] -0.882b[1] 0.216 mm (MJ m-2)-1

r ² 0.999

Global Irrigation Intensity

Kueppers et al, 2007; Siebert et al., 2005

Christy et al., 2006 J Climate

Issues to Consider Regarding Role of C Sequestration to Mitigate Climate Change

• Vegetation operates less than ½ of the year and is a solar collector with less than 2% efficiency– Solar panels work 365 days per year and have an efficiency of 20%+

• Ecological Scaling Laws are associated with Planting Trees– Mass scales with the -4/3 power of tree density

• Available Land and Water– Best Land is Vegetated and New Land needs to take up More Carbon

than current land– You need more than 500 mm of rain per year to grow Trees

• The ability of Forests to sequester Carbon declines with stand age• There are Energetics and Environmental Costs to soil, water, air

and land use change– Changes in Albedo and surface energy fluxes – Emission of volatile organic carbon compounds, ozone precursors– Changes in Watershed Runoff and Soil Erosion

• Societal/Ethical Costs and Issues– Land for Food vs for Carbon and Energy– Energy is needed to produce, transport and transform biomass into

energy