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