1. 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 ERDC 2Mississippi State University 3NASA / GSFC 27 July 2011

2. Outline Motivation and Objective Approach and Description of the SRSS Simulation Results Future Work

3. 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

4. Dry Conditions

5. Moist Conditions Flooded Conditions

6. 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.

7. 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.

8. Research Questions How do you simulate the forest without explicitly simulating the forest? During periods of high mass transfer, how much heat is transported by the fluid flow compared to conduction and radiative effects? What is the effect of the root system on the spatial and temporal distributions of temperature and moisture content in the soil?

9. 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.

10. 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)

11. 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

12. SRSS Component Verification Conduction in unsaturated porous media Radiative heat transfer Sky radiative heat transfer Shortwave solar radiation Convective heat transfer in porous media

13. SRSS Application to Historical Simulations Derby and Gates (1965) Herrington (1964)

14. 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

15. SRSS Application Single tree in a mature deciduous forest Both winter and early summer simulation

16. 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

17. Mesh Development Requirements Realistic trunk and root system Allows anisotropic thermal and fluid properties Hydraulically connected

22. LIDAR Scan of Root System Raw Data Centerline Selection Solid Geometry

26. Stem Cross-Sections

30. Winter

31. Early Summer

32. Simulation Results

33. Early Summer Example

34. Surface Heat Flux

35. Growth of Unsaturated Soil Region

37. Simulation Analyses Temperature profiles along cardinal radius lines Flow vs. no flow Open vs. close canopy

38. N W E S 0.6 Bark Xylem1 5.5 Xylem2 Xylem3 9.4 Heartwood 0.6 9.6 4.8 12.5 3.4 0.8 12.7 8.3 4.8 0.6

39. Winter trunk temperatures North radius at 0.6m South radius at 0.6m

40. Winter thermal radiation 1.3m 0.6m 0.3m

41. Flow effect on Temperature flow no flow flow – no flow Early summer North radius at 0.6m

42. 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

43. Research Answers The SRSS demonstrated the ability to simulate accurately the physics of thermal radiation without explicitly modeling the entire forest. During periods of moderate fluid flow, simulations showed up to a 2 deg C change in temperature accounting for conduction and radiative effects. Fluid flow from the soil into the roots creates unsaturated soil regions that vary diurnally and changes the thermal properties of the soil.

44. 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

45. Thank You

46. Inclusion of understory vegetation

48. Critical Time Steps