SIMULATED SEASONAL SPATIO-TEMPORAL PATTERNS OF SOIL MOISTURE, TEMPERATURE, AND NET RADIATION IN A...

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Simulated Seasonal Spatio-temporal Patterns of Soil Moisture, Temperature,

and Net Radiation in a Deciduous Forest

Jerry Ballard1, Stacy Howington1, Pasquale Cinella2, and Jim Smith3

1US Army ERDC2Mississippi State University

3NASA / GSFC

27 July 2011

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Outline

• Motivation and Objective• Approach and Description of

the SRSS• Simulation Results• Future Work

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Introduction• Both the temperature and moisture regimes in the forest are some of the most important components in forest ecosystem dynamics• Affects:

• Tree growth and development• Onset and cessation of cambial activity• Nesting success of avian species (tree cavities)• Uptake and metabolism of pollutants from the soil• Growth and treeline elevation limitation

• Influences forest fire intensity and tree survivability

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Dry Conditions

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Moist Conditions Flooded Conditions

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Motivation• Both heat and fluid processes are well

studied in trees, but little is known of the interactions of the processes temporally or spatially.

• Some work exists for coupled 1- or 2-D heat and fluid flow in trees, but rarely in three dimensions.

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Objectives• Develop a three-dimensional

computational tool that simulates the radiative energy, conductive heat, and mass transfer interaction in a soil-root-stem system (SRSS).

• Verify process components of the SRSS and apply to a seasonally varying deciduous forest in a temperate environment.

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Research Questions1. How do you simulate the forest

without explicitly simulating the forest?

2. During periods of high mass transfer, how much heat is transported by the fluid flow compared to conduction and radiative effects?

3. What is the effect of the root system on the spatial and temporal distributions of temperature and moisture content in the soil?

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Research Approach• If we treat the behavior of water in the

soil and xylem similarly, it should be possible to model the xylem as a porous medium

• Develop radiative transfer model that estimates infrared contribution from the surrounding environment using form factors derived from hemispherical images

• Construct a macro-scale model of a tree-root-soil system and simulate different seasonal time periods.

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SRSS Components• Radiative Heat Transfer

• Simulates radiative energy in the domain• Simulates solar energy into the domain• Monte Carlo multiprocessor C code

• Heat and Mass Transfer in Porous Media• Simulates time varying thermal and fluid material

properties• Mass and momentum based on Richards’ equation• Multiprocessor C code (ADH)

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Simulation Assumptions• Fluid in the system is constant viscosity and

density• All fluid movement occurs in a porous

medium• Fluid velocities constitute a creeping flow

(Re < 10)• Air is always at atmospheric pressure• No radiative heat transfer occurs in the

pore space in the solids• Within a volume of porous media, the

temperatures of water and air are the same• All surfaces are diffuse and are treated as

grey black bodies• The air gap between surfaces neither

attenuates or emits thermal radiation

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SRSS Component Verification

Radiative heat transferSky radiative heat transfer

Conduction in unsaturated porous media

Shortwave solar radiation

Convective heat transfer in porous media

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SRSS Application to Historical Simulations

Herrington (1964)

0800

0900

1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

Figure 1.1 Temperature contours from the Derby and Gates pine log simulation. Time is in hours and temperature is deg C.

Derby and Gates (1965)

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SRSS Application for a Tree within a Forest

• Simulate a single mature tree• Located in a temperate deciduous

forest• Seasonally and diurnally varying

Time-lapse thermal imagery movie

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SRSS Application• Single tree in a mature

deciduous forest• Both winter and early summer

simulationTable 1.1 Simulation Matrix for the Temperate Forest

Name Seasonal Setting Fluid Flow Soil State Solar Conditions

Alpha Winter N Saturated Winter Canopy Bravo Winter N Unsaturated Winter Canopy Charlie Early Summer N Saturated Summer Canopy Delta Early Summer N Unsaturated Summer Canopy Echo Early Summer Y Saturated Summer Canopy

Foxtrot Early Summer Y Saturated Open Canopy

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Computational Domain• 12x15x8 m domain

• 2-m above soil, 6-m below the soil• Top stem exiting fluid flow driven by time-

varying flow• Bottom of domain

• Saturated soil condition• Constant temperature

• Surface of domain• Modified by diurnal varying solar radiation

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Mesh Development• Requirements

• Realistic trunk and root system• Allows anisotropic thermal and fluid properties• Hydraulically connected

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LIDAR Scan of Root System

Raw Data

Centerline Selection

Solid Geometry

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Stem Cross-Sections

-0.4m -0.3m -0.2m

0.0m 0.3m 0.6m

0.9m 1.3m 1.6m

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Winter

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Early Summer

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Simulation Results

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Early Summer Example

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Surface Heat Flux

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Growth of Unsaturated Soil Region

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Simulation Analyses• Temperature profiles along

cardinal radius lines• Flow vs. no flow• Open vs. close canopy

Table 1.1 Simulation Matrix for the Temperate Forest

Name Seasonal Setting Fluid Flow Soil State Solar Conditions

Alpha Winter N Saturated Winter Canopy Bravo Winter N Unsaturated Winter Canopy Charlie Early Summer N Saturated Summer Canopy Delta Early Summer N Unsaturated Summer Canopy Echo Early Summer Y Saturated Summer Canopy

Foxtrot Early Summer Y Saturated Open Canopy

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N

W E

S

0.8

12.5 3.4

0.6

4.8

8.3

12.7

0.6 4.8 9.6

0.6

5.5

9.4

Bark

Xylem1Xylem2Xylem3Heartwoo

d

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Winter trunk temperatures

North radius at 0.6m

South radius at 0.6m

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Winter thermal radiation

0.3m

0.6m

1.3m

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Flow effect on Temperature

flow no flow

flow – no flow

Early summer

North radius at 0.6m

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Analyses Summary• Winter simulations agree with

observations showing that the primary influence of temperature in the trunk is solar driven.

• Flow in summer simulations show up to a 2 deg C change in internal temperature due to fluid flow

• Both winter and summer simulations show internal temperatures affected by surrounding forest radiation and soil conduction

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Research Answers1. The SRSS demonstrated the ability

to simulate accurately the physics of thermal radiation without explicitly modeling the entire forest.

2. During periods of moderate fluid flow, simulations showed up to a 2 deg C change in temperature accounting for conduction and radiative effects.

3. Fluid flow from the soil into the roots creates unsaturated soil regions that vary diurnally and changes the thermal properties of the soil.

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Future Work• Inclusion of dense

understory vegetation

• Long-term full season simulations

• Drought simulations• Additional validation

studies• Macro vs. micro scale

root fluid uptake analysis needed

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Thank You

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Inclusion of understory vegetation

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Critical Time Steps