global change and agriculture: the effects that plants have on climate, and vice versa dennis...
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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
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