Results

Time

Study Site

Measured data

Alfalfa

Numerical Analysis of Water and Heat Transport in Vegetated Soils Using HYDRUS-1DMasaru Sakai1), Jirka Šimůnek2)

1) Dept. Plants, Soils, and Climate, Utah State University, Logan (m.sakai@usu.edu) 2) Dept. Environmental Sciences, University of California, Riverside

Introduction

Summary

Evaluation of water contents and temperatures in root zone is important for water management of agricultural fields. To simulate water flow, heat transport, and root water uptake simultaneously, the boundary condition at vegetated soil surface evaluated from available meteorological information is necessary. The objective of study is to develop a numerical model that solves water flow, heat transport, and root water uptake with surface energy and water balance. We implemented “Double-Source Model” (Watanabe, 1992), that calculate energy balance at the crop canopy and the soil surface, to the HYDRUS-1D code. Calculated soil temperatures were compared with observed data in a field site.

s as

as s

Er r

Double -Source Model (Watanabe, 1994)

1 exp 0.463SCF LAI

Calculated energy balance component at the soil surface.

Every term decreases with time corresponding to Alfalfa growth.

Observed and Calculated soil temperature. Calculated results show larger daily amplitudes than observed

ones.

The Double-Source Model was implemented in the HYDRUS-1D code, and the energy balance at the soil surface are calculated from meteorological information.

Although calculated soil temperature reasonably agreed with observed one, daily amplitude was larger. Further investigations of parameters in the energy balance equations are needed.

4 41 2c s s s c c c clSCF R SCF R SCF T SCF T H L E

0 0p v v vL

w v

C T q q Tq TTL C L C

t t z z z z z

Lh Lh LT vh vT

h T h TK K K K K S

t z z z z z

Numerical Simulation

Water and vapor Flow

Heat Transport

Energy balance at Crop canopy

Energy balance at Soil surface

4 41 1 1s s c c s s s slSCF R SCF R SCF T T H L E G

4c cSCF T

sSCF R 1 sSCF R l

SCF R 1

lSCF R

4c cSCF T

cH

4s sSCF T

4s sT

sL EsH

cL E

G

Rs :Incoming shortwave radiation

Rl↓ :Downward longwave radiation

G :Surface heat fluxTc :Air temperatureTs :Soil surface temperatureTc :Crop canopy temperatures :Soil surface emissivityc :Crop canopy emissivitys :Soil surface albedo [-]c :Crop canopy albedo [-]L :Latent heat of vaporization

( )vs c ac

ac

TE

r

s as a

hs

T TH C

r

c a

c ahc

T TH C

r

Evaporation Es and Transpiration rate Ec

Sensible heat flux from soil surface Hs and canopy Hc

ras :Resistance for vapor at soil surface

rac :Resistance for vapor at canopy

rhs :Resistance for heat at soil surface

rhc :Resistance for heat at canopy

rs :Soil surface resistance

s :Vapor density at soil surfacea :Atmospheric vapor densityvs (Tc) :Saturation vapor density at canopy :Stefan-Boltzman constantCa :Volumetric heat of air

Es and G for surface boundary conditions from meteorological data

Surface Cover Fraction SCF

Field data

Boundary Conditions

Sandy Loam

70 cmSand

80 cm

Silt Loam

0 cm

(Segal et al., 2008)

•Solar Radiation•Relative Humidity•Wind Speed•Air Temperature•Irrigation rate

(every 15 minutes)

•Alfalfa Field in San Jacinto, California (33º55'22''N, 117º00‘46''W)•220 cm depth water table

•Soil temperature•Pressure head

References•Watanabe, T. (1994): Bulk parameterization for a vegetated surface and its application to a simulation of nocturnal drainage flow. Boundary-Layer Meteorol., 70: 13-35.•Segal, E., S.A. Bradford, P. Shouse, N. Lazarovitch, and D. Corwin (2008): Integration of hard and soft data to characterize field-scale hydraulic properties for flow and transport studies, Vadose Zone Journal., 7: 878-889.

•Alfalfa was harvested July 24th and grew up after July 25th •Reference values were used for crop height and root depth

July 25th – September 2nd

210 215 220 225 230DO Y

15

20

25

30

35

40

So

il t

emp

erat

ure

(°C

)

observedCalculated

30cm depth

210 215 220 225 230DOY

15

20

25

30

35

40

So

il te

mp

era

ture

(°C

)

observedCalculated

10cm depth

210 215 220 225 230DOY

0

1

2

3

4

Su

rfac

e fl

ux

(cm

/day

)

Evaporation form soil surfaceTranspiration (Root water uptake)

210 215 220 225 230DOY

-20

0

20

40

60

Hea

t F

lux

(MJ/

m2 /

day

)

Net RadiationSensible Heat FluxLatent Heat FluxSurface Heat Flux

Calculated evaporation rate from soil surface and transpiration rate from canopy.

Surface heat flux

B.C. for heat transport

Evaporation rate

B.C. for water flow

Transpiration rate

Root water uptake

HYDRUS Interface

-350 -300 -250 -200 -150 -100Pressure head (-cm )

80

60

40

20

0

Dep

th(c

m)

DOY 210.5220.5225.5230.5

0 0.002 0.004 0.006 0.008Root water uptake (d -1)

80

60

40

20

0

Dep

th(c

m)

DOY 210.5220.5225.5230.5

0.1 0.2 0.3 0.4 0.5W ater content (-)

80

60

40

20

0

Dep

th(c

m)

DOY 210.5220.5225.5230.5

Calculated profiles of pressure head, water content, and root water uptake.

2

1ln ( ) ln ( )ref h ref m

h a h mh m

z d z z d zr r

uk z z

2

1 1ln ( ) ln ( )

1ref h ref m

as hs h g m gh m

z d z z d zr r

SCF uk z z

1 1 1 1 1 1;

hc h hs ac a asr r r r r r

Aerodynamic Resistance

Between soil and atmosphere

0 0.2 0.4 0.6 0.8 1SCF (-)

0

200

400

600

800

1000

Ae

rod

yn

am

ic r

esis

tan

ce

, r (

sm

-1)

ras=rhs

rac=rhc

Between entire surface (soil and canopy) and atmosphere

Between canopy and atmosphereu :Wind speedk :Karman constant (=0.41)zref :Reference heightd :Zero-plane displacement heightzh, zm :Surface roughtness for heat flux and momentumh, m :Atmospheric stability correction factor Relationship between resistances and SCF