Simulation of crop

evapotranspiration for an almond

orchard using the ACASA model

Matthias Falk

CSTARS, LAWR, UC Davis

Advanced Canopy-Atmosphere-Soil Algorithm (ACASA)

ACASA uses fully diabatic, turbulent steady-state equations closed at the third order for

estimating energy and mass fluxes and profiles for each layer, placing it among the most

complex SVAT models.

GOALS

1. Test ACASA for an irrigated agricultural crop canopy such as almonds

2. Evaluate model performance by comparing simulated energy and mass exchanges

(flux densities) with long-term Eddy Covariance flux measurements

3. Validate the use of ACASA to show suitability as a surface layer scheme in WRF-

ACASA to provide more accurate estimates of spatial crop evapotranspiration (ETc)

QUESTION:

WHY DO WE NEED SO MUCH PHYSICS?

Introduction

Location overview: (A) CIMIS Belridge and (B) Belridge Kc-testing EC tower site

Eddy-Covariance Tower at Belridge BE_004

Almonds, zc = 5.5 meters, LAI ~ 1.5 m2m-2

Jan

2009

Feb

2009

Mar

200

9Ap

r 200

9M

ay 2

009

Jun

2009

Jul 2

009

Aug

2009

Sep

2009

Oct 2

009

Nov

200

9Dec

200

9

30

40

50

250

500

750

Tair [oC]

Month Year

Tair

CIMIS Belridge (# 146)

0

5

10

15

20

25

30

35

[mm]

Precip ETo

[Ly/Day]

Rsolar

Jan

2008

Feb

2008

Mar

200

8Ap

r 200

8M

ay 2

008

Jun

2008

Jul 2

008

Aug

2008

Sep

2008

Oct

200

8Nov

200

8Dec

200

8

30

40

50

250

500

750

Tair [oC]

Month Year

Tair

CIMIS Belridge (# 146)

0

5

10

15

20

25

30

35

ETo, Pcp [mm]

Precip ETo

Rs [Ly/Day]

Rsolar

ANNUAL CLIMATE DIAGRAMS FOR BELRIDGE CIMIS STATION (#146) FOR 2008 AND 2009

Monthly Values for Average Air Temperature (Tair), Total Precipitation (Precip),

Average Incoming Solar Radiation (Rs) and Total Reference Evapotranspiration (ETo)

Climate

Belridge CIMIS Station (CIMIS #146)

Climate: Hot Semi-arid climate or Hot-Summer Mediterranean climate

Averages calculated for data from 1998 through 2010:

Annual Average Temperature: 17.26 oC

Average Annual Total Precipitation: 133.62 mm or 5.26 inches

Average Annual Total CIMIS ETo: 1495.98 mm or 58.9 inches

Annual Irrigation: 50+ in; so about 10x Precipitation

Climate

ACASA Description

10 Leaf Classes:

• 9 different leaf angles

• 1 shaded leaf

(not angle dependent)

METEOROLOGY (hourly)

Temperature (Tair),

Relative Humidty (RH),

Wind Speed (u),

Solar Radiation (Rs)

Precipitation (pcp)

Pressure (p) ~ const.

CO2-Concentration (CO2) ~ const.

Downwelling Longwave Radiation (Ld) – modeled

NEW: Leaf Area Index (LAI(t))

ACASA Input

3600.0 !deltat1 REAL time step length (s) [900,7200]

35.509 !zlatude REAL latitude (oN) [-90,90]

8760 !ntimesteps INTEGER total number of time steps in forcing dataset [any]

1 !needtinf INTEGER ?need input downward LW radiation?(1='yes',0='no') [0,1]

1 !ihumid INTEGER ?is input humidity relative(RH%)?,1='yes', RH(%)-->(g kg-1); 0='units (g kg-1) already' [0,1]

1 !iprint7 INTEGER ?extra output? 1='yes', 0='no'

8 !isoi3 INTEGER soil type (USDA 16 classification) [1,16]

4 !nsoil0 INTEGER total number of soil layers [4,20]

3 !nroot INTEGER total number of active root layers (KEEP

ACASA Input

METEOROLOGY – ACASA needs high temporal resolution and continuous data

BELRIDGE CIMIS STATION (#146) – 1998 to present

Ta, RH, u, Rs

ACASA Input

50 100 150 200 250 300 350

0

200

400

600

800

1000

1200R

s [Wm

-2]

DOY 2008

Rs CIMIS

Figure 1: CIMIS hourly incoming solar radiation (Rs) for 2008

?

ACASA Input

0 60 120 180 240 300 360

0

50

100

150

200

250

300

350

400Daily average R

s (Wm

-2)

DOY 2008

Rs CIMIS

Rs SpatialCIMIS

Figure 2: Daily Average Values for ground based and satellite based estimates of Rs in 2008 showing sudden drop in CIMIS Rs values.

Practical application for the usefulness of

remotely sensed products in micrometeorological studies

ACASA Input

0

50

100

150

200

250

300

350

400

0 50 100 150 200 250 300 350 0 50 100 150 200 250 300 350

0

50

100

150

200

250

300

350

400CIM

IS Belridge Station

(daily average R

s (a) and filtered (b))

Sol Rad (W/m^2)

Sol Rad (W/m^2)

CIMISspatial

Original Filtered

Sol Rad (W/m^2)

CIMIS spatial

Equation y = a + b*x

Weight No Weighting

Residual Sum of Squares

74598.5999

Adj. R-Square 0.97577

Value Standard Error

Smoothed Y1 Intercept -32.50571 2.25941

Smoothed Y1 Slope 1.11789 0.0097

Figure 3: Scatter plot of daily average Rs from CIMIS and CIMISspatial

ACASA InputRenormalize the hourly CIMIS Rs data:

Rs,corrected,hourly = Rs,CIMIS,hourly / Rs,CIMIS,daily * Rs,CIMISspatial,daily

120.0 120.2 120.4 120.6 120.8 121.0

0

200

400

600

800

1000

1200

Rs [Wm

-2]

DOY 2008

Rs (corrected)

Rs (CIMIS)

60 120 180 240 300 360

0

200

400

600

800

1000

1200

Hourly R

s [Wm

-2]

DOY 2008

Rs,corrected

Rs,CIMIS

Figure 6: Hourly values of CIMIS Rs for 2008. Original data in blue with corrected values in red.

ACASA Input

120.0 120.2 120.4 120.6 120.8 121.0

0

200

400

600

800

1000

1200Rs [Wm

-2]

DOY 2008

Rs corrected,daily

Rs CIMIS

Rs GOES

Figure 7: Diurnal for Rs on Julian Day 120, 2008 showing hourly values for CIMIS, corrected CIMIS and GOES based estimates.

92 94 96

0

200

400

600

800

1000

1200

Rs [Wm

-2]

DOY 2008

Rs corrected,daily

Rs CIMIS

Rs GOES

ACASA Input

Figure 8: Time series showing the three different estimates or Rs from CIMIS, corrected CIMIS and GOES

0

200

400

600

800

1000

0 200 400 600 800 1000

Good: RsCIMIS

=0.973(+-0.007) * RsGOES

; R2=0.99

Bad: RsCIMIS

=0.811(+-0.005) * RsGOES

; R2=0.99

good

bad [94 < DOY < 117]

Linear Fit of good

Linear Fit of bad

Rshourly,GOES

[Wm-2]

Rshourly,CIMIS [Wm

-2]

Figure 9: Scatter plot of GOES and CIMIS hourly estimates of Rs. Data from the period of bad CIMIS data are

plotted in red and data from the rest of the year in black. Linear fit analysis was performed for both data sets.

ACASA Input

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 60 120 180 240 300 360DOY

LAI 2009

LAI ACASA

LAI 2008

LAI (m

2/m2)

LAI

ACASA Input

130 131 132 133 134 135

-400

-200

0

200

400

600

800

Rn, LE [W m

-2]

day_of_year 2008

Rn ACASA LE ACASA

Rn EC LE EC

196 197 198 199 200

-400

-200

0

200

400

600

800

Rn, LE [W m

-2]

day_of_year 2008

Rn ACASA LE ACASA

Rn EC LE EC

ACASA Results

Surface Energy Balance

Rn – G = H + LE

Measured quantities (Kc testing):

Rn: Net Radiation (radiometer)

G: Ground Heatflux (ground heat flux plates)

H: Sensible Heatflux (sonic anemometer)

LE = ETc is the residual

LE = Rn - G - H

130 131 132 133 134 135

-400

-200

0

200

400

600

800

Rn, LE [W m

-2]

day_of_year 2008

Rn ACASA LE ACASA

Rn EC LE EC

ACASA Results

Spike in hourly Ground Heat

Flux due to sun-spots on

the orchard floor

Spike in hourly ETc

due to sun-spots on the

orchard floor

-200 0 200 400 600 800

-200

0

200

400

600

800 Rn=NetRadiation

Rn [Wm

-2]

ACASA

Rn [Wm-2]

EC

Equation y = a + b*x

Weight No Weighting

Residual Sum of Squares

9.88926E6

Adj. R-Square 0.97461

Value Standard Error

Rn=NetRadiatio Intercept -23.21348 0.68567

Rn=NetRadiatio Slope 1.00743 0.00218

ACASA Results

The only ACASA inputs: No longwave observations, $200 pyranometer plus leaf + canopy parameters

ACASA Results

-200 0 200 400 600 800

-200

-100

0

100

200

300

400

500

600

700

800

LE=LatentHeat [W

m2]

ACASA

LE=LatentHeat [W m2]

Eddy Covariance (Residual LE=Rn-G-H)

Equation y = a + b*x

Weight No Weighting

Residual Sum of Squares

1.77595E7

Adj. R-Square 0.94612

Value Standard Error

LE=LatentHeat Intercept 0 --

LE=LatentHeat Slope 0.96742 0.00334

Equation y = a + b*x Var. Intercept

Weight No Weighting

Residual Sum of Squares

1.402E7

Adj. R-Square 0.91442

Value Standard Error

LE=LatentHeat Intercept 32.15875 1.04147

LE=LatentHeat Slope 0.88973 0.00394

50 100 150 200 250 300 350

0.00

0.25

0.50

0.75

1.00

1.25

1.50

0

10

20

30

39

49

59

ET [in]

ET [m]

DOY 2008

start at DOY 100

complete data year

2008 Growing season ET = 41.59 in / 1056 mm

ACASA modeled ET for Belridge Almond Orchard

ACASA Results

ACASA Results

0 60 120 180 240 300 360

0

10

20

30

40

50

60

70

0

10

20

30

40

50

60

70

day_of_year, 2009

ACASA_ETc

ΣETc [in]

EC_ETc

ETo (CIMIS) ETc (EC) ETc (ACASA) Irrigation

ET (in) 2008 39.09 40.79 41.59 40.40

ET (in) 2009 38.7 41.8 43.24 39.62

CIMIS: Reference Evapotranspiration from the Belridge CIMIS station

EC: Evapotranspiration from Sonic Anemometer system on the Kc-testing tower

Irrigation: Total Applied Irrigation for the growing season

ACASA: Evapotranspiration Estimate based on the UC Davis ACASA model

Estimates of evapotranspiration (ETc) from different methods for the Almond

Orchard in 2008 (DOY 81 through 244) and 2009 (DOY 79 through 244)

ACASA Results

Conclusions

RESULTS

1. With very few modifications ACASA ETc

simulations for an irrigated almond

orchard work.

2. We evaluated the model performance

by comparing simulated energy and

mass exchanges (flux densities)

derived from an independent

meteorological data set (CIMIS) with

long-term Eddy Covariance flux

measurements (Kc testing) with very

good results

3. Used remotely sensed products! ☺

WHY DO WE NEED SO MUCH PHYSICS?

BECAUSE IT WORKS BETTER!