SiSPAT-Isotope model
Better estimates of E and T
Jessie Cable
Postdoc - IARC
Very green landscapes that are fluxing water to the atmosphere
- Combination of vascular and non-vascular plants
- Different water flux dynamics necessitate distinguishing between them
(E and T vs. ET)
Transpiration
Transpiration =
Plants control the water
vapor flux
Evaporation
Evaporation = mosses
are an evaporating
surface (BUT, they are
NOT bare ground)
http://www.marietta.edu/~biol/biomes/imag
es/wetlands/sphagnum_6449a_A80.jpg
TRANSPIRATION
5
4
BIRCH-WILLOW SHRUB ECOSYSTEM
Dwarf Birch
Blueberry
Willow
Bow Willow
Labrador Tea
3
2
6
5
TRANSPIRATION
6
1
Black Spruce
Cranberry
Labrador Tea
Blueberry
2
3
2
5
TRANSPIRATION
TRANSPIRATION
3
0
BLACK SPRUCE ECOSYSTEM
4
4
Dwarf Birch
Black Spruce
Cranberry
Labrador Tea
Willow
Blueberry
1
0
5
BLACK SPRUCE ECOSYSTEM
WITHOUT DEGRADING PERMAFROST
4
3
2
1
1
0
0
5/25/09 6/8/09 6/22/09 7/6/09 7/20/09 8/3/09
BLACK SPRUCE ECOSYSTEM
WITH DEGRADING PERMAFROST
6/1/09
6/15/09 6/29/09 7/13/09 7/27/09 8/10/09
Need better assessment of E and T
Rainfall recycling and watershed/soil water
balance
Changes in landscape / vegetation
distributions impact magnitude and
partitioning of ET
ET
Tape et al. 2006
CREW-NASA
Need more accurate representation of E and
T in atmosphere, hydrological, or
vegetation growth models
• Little data exist to validate the
partitioning of E and T in SVAT
(Soil Vegetation Atmosphere
Transfer) models
• Concentration measurements of
stable isotopes of water in soil,
plants, and vapor can aid in
partitioning / quantifying E and T
– E and T differentially impact
concentration of isotopes in soil or
vapor
• soil stable isotope
concentrations useful for
– determining plant rooting profiles
(for validation of root extraction
submodels in SVAT)
– better quantification of water
transfer within soils (vapor diffusion
coefficients and hydraulic
properties)
H2 O
1H, 2H
16O, 18O
SiSPAT-Isotope model
Braud et al., Journal of Hydrology 309 (2005) 277-300, 301-320
• Modification of the pre-existing 1D SiSPAT model (Simple Soil Plant
Atmosphere Transfer model) to include transport of stable isotope species to
better estimate E and T
• Coupled heat, water, and isotope transport equations solved for temperature
and matric potential and isotope profiles
• forced by air temp, humidity, wind speed, incoming solar and long wave
radiation, rainfall
• bare ground, saturated
soils, steady state
conditions (equilibrium
between vapor and
liquid phases for
isotopes)
• Currently focused on
estimating kinetic
fractionation coefficient
Issues with adding isotope transport
1H, 2H
• Correctly accounting for fractionation
16O,
associated with molecular diffusion
• turbulent vs molecular diffusion affecting
resistance to isotope vapor flux
• Need a plant component and proper
treatment of plant physiology
• Kinetic fractionation factor for drying soils
and non-saturated conditions
18O
Data-model integration issues
• The solution of the isotope
species transport equation
requires high resolution of
the vertical profile near the
surface (particularly to
capture the vapor return)
• Problem: require fine time
steps that field sampling
can not yet provide
Species
spruce
rubus
ledum
betula
post rain
pre rain
0-5
5-10
Depth (cm)
10-20
20-30
30-40
40-50
50-60
60-70
post-rain
pre-rain
70-80
80-100
-180
-170
-160
-150
-140
D ( /00)
0
-130
-120
-110