Evidence for the Influence of AgricultureOn Weather & Climate
Through theTransformation & Management of Vegetation
: illustrated by examples from the Canadian Prairies
Evidence for the Influence of AgricultureOn Weather & Climate
Through theTransformation & Management of Vegetation
: illustrated by examples from the Canadian Prairies
R. L. RaddatzR. L. RaddatzHydrometeorology and Arctic LaboratoryHydrometeorology and Arctic LaboratoryMeteorological Service of CanadaMeteorological Service of Canada
Land Surface – Atmosphere Interaction
Moisture (mass) balance of surface layer of the land:
P = I + E + T + R + D +∆Sw
Surface energy balance:
Q* = QG + QH + QE
Moisture (mass) balance of the atmosphere:
P = E + T + ( F+ - F- ) + ∆Sv
+ Impact of vegetation on soil moisture
Main Properties of Vegetation (that influence the transfer of heat, moisture and momentum from land surface to overlying air)
Physiological - leaf area - stomatal resistance - rooting depth
Physical - albedo - roughness length
(Arora, 2002)
Including Irrigation
Vegetation Transformation & Managementby Agriculture
15-18 million km2
Cropland (12%)
34 million km2
Pasture & Range Land (22%)
(Leff et al., 2004)
Illustrative examples from: Cropped Grassland Eco-climatic Region Canadian Prairies Provinces
50% of area inannual field crops
Annual field cropsare a primary sourceof Evapotranspiration
HB sHB sHB sLSHSMB sLBGtGa
##
#
#
#
#
#
#
#
Fort McMurray
Edson
Churchill
Thompson
WinnipegSwift Current
Ga Gt
LB
MBs
SC
HBs
LS
HS
100 0 100 200KmScale
Legend
LBs - Low BorealLS - Low SubarcticMBs - Subhumid Mid-BorealSC - Southern Cordilleran
Ga - Arid GrasslandGt - Transitional GrasslandHBs - Subhumid High BorealHS - High Subarctic
Key Map
1st Generation Prairie Crop Phenology & Water Use Model1st Generation Prairie Crop Phenology & Water Use Model
Vegetation Weather Soil- spring wheat - daily precipitation - available water- Perennial grasses - maximum temperature holding capacity - minimum temperature - incidental solar radiation - photoperiod
PotentialEvapotranspiration
Initial Soil Moisture
Heat Units
Vegetative Cover
Available Soil Moisture
Water-Use
Planting Date
Consumptive Use Water-Demand
Rooting Depth
Precipitation
Water BalanceModel
PBL Module Soil Moisture ModuleGrowth Module
Planting DatesInitial SoilMoisture
Crop StageVapour Deficit & Aerodynamic
Resistance
Top-Zone Root-Zone
Leaf-Area
RootingDepth
Soil Resistance&
Skin Humidity
CropWater-Demand
CanopyResistance
Crop Water Use
2nd Generation Prairie Crop Phenology & Water Use Model
Crop•Wheat• Canola•Potatoes
Weather•Daily Precipitation•Daily Temperature Extremes•Gridded upper-air data•Photoperiod
Soil•Soil Textural Class•Terrain Heights•Drag coefficients
ColumnModel
Often via the Vegetation (Basara & Crawford, 2002)
strong linear relationship between root-zone soil moisture and - Evaporative fraction ETf = QL / ( QH + QL ) - Near surface - maximum temperatures - afternoon mixing ratios - Boundary layer - mean potential temperatures - mean mixing ratios correlation with top zone soil moisture was weak and non-linear
Land Surface – Atmosphere Coupling
Impact ofAnnual Crops(and green-up ofDeciduous Trees)
on theEvaporative Fraction
Spring WheatWinnipeg 1988-2000
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
1-M
ay
8-M
ay
15-M
ay
22-M
ay
29-M
ay
5-J
un
12-J
un
19-J
un
26-J
un
3-J
ul
10-J
ul
17-J
ul
24-J
ul
31-J
ul
7-A
ug
14-A
ug
21-A
ug
28-A
ug
4-S
ep
11-S
ep
18-S
ep
25-S
ep
2-O
ct
Week Ending
Weekly
Evap
otr
an
sp
irati
on
(m
m)
Mean
+2 Standard deviations
-2 standard deviations
Lower mean afternoon mixing-layerdepths in June & July than in May dueto increase QL and reduced QH
due to transpiration from annual fieldcrops and from aspen groves
July 10
July 10
Cropped Transitional GrasslandCanadian Prairies
1335 CSTMax area
1005 CSTNo cloud
1135 CSTInitiation
Initiation of ConvectionWith Weak Synoptic Forcing
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
90.0%
100.0%
0900 1000 1100 1200 1300 1400 1500 1600 1700
Initiation Time (CST)
Ro
ot
Zo
ne
Mo
istu
re (
%)
Time of convective initiation more highly correlatedwith root-zone than with top-zone soil moisture
Occurs, primarily, via the vegetation.
Atmospheric Boundary Layer – Soil Moisture Coupling
R = 0.77
Swift Current - Spring Wheat
0
50
100
150
200
250
1-Ju
n
8-Ju
n
15-J
un
22-J
un
29-J
un6-
Jul
13-J
ul
20-J
ul
27-J
ul
3-Aug
10-A
ug
17-A
ug
24-A
ug
31-A
ug
1999
So
il M
ois
ture
(%
Ca
pa
cit
y) Root Zone
Top Zone
Where annual crops dominate the vegetation, the primary cumulus convection – soil moisture feedback occurs on the seasonal time scale.
Cumulus Convection – Soil Moisture Feedback
Agriculture & Weather and Climate
Through agriculture (land clearing, cultivation, and the grazing ofdomesticated animals), man has transformed, and now manages tovarying degrees, the vegetation (i.e., the physiological and physicalproperties of the land cover), and directly (via irrigation) or indirectly(via the vegetation) the soil moisture over large tracks of land.
By altering the properties of the vegetation, agriculture influences themagnitude of the net radiation (via surface albedo), and how this energyis partitioned into sensible and latent heat fluxes (via stomatalresistance). It may also influence the vertical flux of momentum(via the roughness length).
Agriculture also has an impact upon the aerodynamic coupling betweenthe land surface and the atmosphere (via aerodynamic resistance),and, thus, it has a further impact on the surface fluxes.
Evidence for the Influence of Agriculture on Weather & Climate
1. Agriculture’s Influence on Near Surface Weather Elements.
2. Agriculture’s Influence on the Regional Hydrologic Cycle** 3. Agriculture - Tele-connections & Inter-seasonal Influence.
Tables:(Extensive but not comprehensive)
Region | Ag-Impact | Wx Element | Obs or Mdl | Author
Framework for Grouping Studies
Transitional Grassland
0
20
40
60
80
100
120
140
10-A
pr
24-A
pr
08-M
ay
22-M
ay
05-J
un
19-J
un
03-J
ul
17-J
ul
31-J
ul
14-A
ug
28-A
ug
11-S
ep
25-S
ep
09-O
ct
23-O
ctGrowing-Season
W /
sq. m
Latent Heat ( Grass )
Latent Heat ( Wheat )
Net Radiation ( Grass )
Net Radiation ( Wheat )
(1988-1995)
Agriculture’s Influence on Tmax & Afternoon Mixing Ratios
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
10-A
pr
24-A
pr
08-M
ay
22-M
ay
05-J
un
19-J
un
03-J
ul
17-J
ul
31-J
ul
14-A
ug
28-A
ug
11-S
ep
25-S
ep
09-O
ct
23-O
ct
Deg
rees
C
Incremental ChangeMean Daily Maximum Temperatures & Afternoon Mixing Ratios
DrierDrier
More Humid
Plains-to-Mountains Circulation(Influence adjacent areas - Local effects become regional effects)
Impact uponPlain’s Vegetation
Influence onFoothills Weather
Stohlgren et al., 1998Chase et al, 1999Strong, 2000
(1) Affects the availability of convective energy (CAPE).
(2) Affects the availability of water vapour (Recycling Ratio).
(3) Spatial discontinuities in vegetation and/or soil moisture can induce mesoscale thermal circulations (land-land breezes) that initiate moist deep convection.
Agriculture’s Influence upon the Regional Hydrologic Cycle
Moist deep convection
Convective Rainfall
Severe Weatherfrom Thunderstorms - Flooding - Hail - Tornadoes - etc.
- Results from the release of CAPE when boundary-layer air parcels lifted to level of free convection by a dynamic or thermal mechanism.
Pielke et al, 2001
Cropped Grassland Eco-climatic Region – Canadian Prairies
ET = f (Weather, Vegetation Phenology & Soil Moisture)
Cropped Grassland Eco-climatic Region – Canadian Prairies
ET = f (Weather, Vegetation Phenology & Soil Moisture)
Q* = QG + QH + QE
Evapotranspiration from the annual field crops controls the seasonal pattern of the partitioning of the surface net radiation.
Sensible Heat
LatentHeat
Net Radiation
Bowen Ratio = Sensible Heat Latent Heat
whereBo > 1.0 (Sensible > Latent ) Bo < 1.0 (Latent > Sensible)
Lifted Index : LI = T50 - TparcelLifted Index : LI = T50 - Tparcel
A widely used measure of the amount of CAPE for the development of moist deep convection
LI > 0
LI = 0 to -3
LI < -3
Change to Lifted Index ( Boundary-Layer Depth = 1000m )
0
0.5
1
1.5
2
2.5
500 600 700 800 900
Noon Global Radiation ( W / sq. m )
Bo
we
n R
ati
o
-4-3-2-1
Reduction in Lifted Index due to Regional EvapotranspirationReduction in Lifted Index due to Regional Evapotranspiration
Reduction LI = Increase CAPE
(Segal et al, 1995)
Bowen Ratio
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
10-
Ap
r
24-
Ap
r
08-
May
22-
May
05-
Ju
n
19-
Jun
03-J
ul
17-J
ul
31-J
ul
14-A
ug
28-
Au
g
11-
Se
p
25-
Se
p
09-
Oc
t
23-
Oc
t
Growing- season
Bo
wen
Ra
tio
Wheat
Grasses
Transitional Grassland
Example: CAPE highly sensitive to low-level moisture
Evapotranspitationattributed to Agro-ecosystem
Specific Humidity of CBL
Convective Available Potential Energy (CAPE)
4 mm d-1
11 to 15 g kg-1
Winnipeg $60 millionHail Storm
1400 to 3200 J kg-1
July 16, 1996
1988-2000 Mean
0
1
2
3
4
5
01-M
ay
08-M
ay
15-M
ay
22-M
ay
29-M
ay
05-J
un
12-J
un
19-J
un
26-J
un
03-J
ul
10-J
ul
17-J
ul
24-J
ul
31-J
ul
07-A
ug
14-A
ug
21-A
ug
28-A
ug
04-S
ep
11-S
ep
18-S
ep
25-S
ep
02-O
ct
Week Ending
Wee
kly
Me
an D
aily
Inc
reas
e (g
kg-1
pe
r 1
000
m)
Ave
rag
e N
um
be
r o
f D
ays
per
We
ek
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Wee
kly
Fra
cti
on
al C
on
sum
pti
ve
Us
e
Tornadoes (Ga &Gt)
Specific Humidity (Gt)
Specific Humidity (Ga)
Wheat Phenology (Gt)
Wheat Phenology (Ga)
Demonstrates link between regional evapotranspiration from cropsand moist deep convection
1988
0
1
2
3
4
5
6
01-M
ay
08-M
ay
15-M
ay
22-M
ay
29-M
ay
05-J
un
12-J
un
19-J
un
26-J
un
03-J
ul
10-J
ul
17-J
ul
24-J
ul
31-J
ul
07-A
ug
14-A
ug
21-A
ug
28-A
ug
04-S
ep
11-S
ep
18-S
ep
25-S
ep
02-O
ct
Week Ending
We
ekl
y M
ean
Da
ily In
cre
ase
(g k
g-1 p
er
10
00m
) N
um
be
r o
f D
ays
pe
r W
eek
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
Wee
kly
Fra
ctio
na
l Co
ns
um
pti
ve
Us
e
Tornadoes (Gt & Ga)
Specific Humidity (Gt)
Specific Humidity (Ga)
Wheat Phenology (Gt)
Wheat Phenology (Ga)
1993
0
1
2
3
4
5
6
02-M
ay
09-M
ay
16-M
ay
23-M
ay
30-M
ay
06-J
un
13-J
un
20-J
un
27-J
un
04-J
ul
11-J
ul
18-J
ul
25-J
ul
01-A
ug
08-A
ug
15-A
ug
22-A
ug
29-A
ug
05-S
ep
12-S
ep
19-S
ep
26-S
ep
03-O
ct
Week Ending
Wee
kly
Me
an D
aily
Incr
eas
e (g
kg-1
per
1000
m)
Nu
mb
er o
f D
ays
pe
r W
eek
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
Wee
kly
Fra
cti
on
al C
on
sum
pti
ve
Us
e
Tornadoes (Gt & Ga)
Specific Humidity (Gt)
Specific Humidity (Ga)
Wheat Phenology (Gt)
Wheat Phenology (Ga)
Regional Atmospheric Water BalanceRegional Atmospheric Water Balance
Re
F+
ETRi
F+ = horizontal influx of water vapourF- = horizontal efflux of water vapour Re = areal average rainfall from external moistureET = areal average or regional evapotranspirationRi = areal average rainfall from internal moisture
F-
(Budyko, 1982, Brubaker, 1993, Trenberth, 1999)
Summer Recycling Ratio for RegionSummer Recycling Ratio for Region
Ri / R = 1 / ( 1+ ( 2F+ / (ET*A ))
where ( R = Re + Ri )
Relative contribution of water vapour from regional evapotranspiration to total rain
Measure of importance of evapotranspiration to the regional hydrologic cycle.
##
# #
# #
Boreal
Grassland
* *
* ***
“q” is liquid equivalent of the water vapour in the atmospheric column ( 100 to 25 kpa ) .
“u” & “v” are vertical mean, with mixing ratio weighting, wind components.
Advection or Horizontal Flux ( F + and F- )Advection or Horizontal Flux ( F + and F- )
Wheat Modeling Sites
Rainfall & Land-use weighted Evapotranspiration
Summer Recycling Ratio for RegionSummer Recycling Ratio for Region
Summer Recycling Ratio 1997 24% 1998 35% 1999 25%
(Bosilovich & Schubert, 2002 Summer recycling ratio for western Canada (1990-1995) is 29%.
Regional ET (i.e., recycled regional moisture)is a significant source of water vapour mass forsummer rainfall.
Canadian Prairies 1997 - 2003
y = 0.1256x + 130.19
R2 = 0.0312
0
50
100
150
200
250
300
350
400
450
100 200 300 400 500 600 700 800
Influx (mm)
Rai
n (
mm
)
June – July - August
Canadian Prairies 1997 - 2003
y = 3.8372x + 2.7507
R2 = 0.521
0
50
100
150
200
250
300
350
400
450
0 10 20 30 40 50 60 70 80
Local Moistening Efficiency (%)
Rai
n (
mm
)
June – July - August
M = ET*L / FTrenberth, 1999
Cropped GrasslandEco-climatic RegionCanadian Prairies
poor correlation between horizontal influx (advection) of moisture and summer rain.
good correlation between regional moistening efficiency and summer rainfall, where
M = ET*L / F, and
ET = f (crop stage, soil moisture)
Agriculture’s Influence on Mesoscale Thermal Circulations
Spatial discontinuities in vegetation and/or soil moisture can inducemesoscale thermal circulations (land-land breezes) that may initiatemoist deep convection.
(Segal & Arritt, 1992; Lee & Kimura, 2001).
Sensible Heat Flux
Meso-scale circulation induced by ET discontinuity
Land – Land Breeze
Mixing-Layer Depth
Sensible Heat Flux
Wet | DryMeso-scale circulation induced by ET discontinuity
Land – Land Breeze
Mixing-Layer Depth
1335 CSTMax area
1005 CSTNo cloud
1135 CSTInitiation
Tele-connections
Thunderstorms are conduits for heat & moisturefrom lower to higher altitudes. Thus, spatiallycoherent and persistent patterns of moist deepconvection, in the tropics and during mid-latitudesummers, may influence the ridge and troughpositions in the polar jet stream.
Agriculture, by having an impact upondeep convection, particularly in Tropics,can affect the weather on a global scale.
(Chase et al., 1996; Chase et al., 2000; Zhao et al., 2001)
Inter-Seasonal Influence
A high level of root-zonesoil moisture in the spring,and vegetation to transferthat moisture to theatmospheric boundary layerduring the growing season,are necessary, though notsufficient, conditions for aconvectively active summer.
May 31, 2002
May 30, 2004
( Shukla & Mintz, 1982;Timbal et al., 2002;Koster and Suarz, 2004;GLACE Team, 2004)
Soil Moisture Hot Spots(Global Land Atmosphere Coupling Experiment)
- Regions where soil moisture anomalies have a substantial impact on summer rainfall.
- Transition zones between wet & dry areas where adding moisture to the boundary layer can lead to moist deep convection and where ET is relatively high but still sensitive to soil moisture.
-Through agriculture (land clearing, cultivation, and the grazing of domesticated animals), man has transformed, and now manages to varying degrees, the vegetation and directly (via irrigation) or indirectly (via the vegetation) the soil moisture over large tracks of land.
Soil Moisture (June 1) and Summer Rain1997 - 2003
y = 0.4464x + 165.45
R2 = 0.0231
0
50
100
150
200
250
300
350
400
450
0 20 40 60 80 100 120
Soil Moisture (%AWC; Continuously Cropped; 120 cm)
Rai
n (
mm
)
Canadian Prairies 1997 - 2003
y = 3.8372x + 2.7507
R2 = 0.521
0
50
100
150
200
250
300
350
400
450
0 10 20 30 40 50 60 70 80
Local Moistening Efficiency (%)
Rai
n (
mm
)
Cropped GrasslandEco-climatic RegionCanadian Prairies
good correlation between regional moistening efficiency and summer rainfall, where ET = f (crop stage, soil moisture) poor correlation between spring soil moisture and summer rainfall.
Thus, agriculture influences the current season’s convective rainfall, but the inter-seasonal influence is weak.
M = ET*L / F
Evidence for the Influence of Agriculture on Weather & Climate
1. Agriculture’s Influence on Near Surface Weather Elements.
2. Agriculture’s Influence on the Regional Hydrologic Cycle** 2.1 Convective Available Potential Energy (CAPE) 2.2 Regional Moisture Recycling 2.3 Mesoscale Thermal Circulations
3. Agriculture - Tele-connections & Inter-seasonal Influence.
Tables: (Extensive but not comprehensive)
Region | Ag-Impact | Wx Element | Obs or Mdl | Author
Framework for Grouping Studies
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