Hydrologic effects and implications of vegetation in semiarid mountain regions Huade Guan Advisor:...
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Transcript of Hydrologic effects and implications of vegetation in semiarid mountain regions Huade Guan Advisor:...
Hydrologic effects and implications of vegetation in semiarid mountain regions
Huade GuanAdvisor: Dr. John Wilson
SAHRA 4th Annual meetingOct. 15, 2004
South Baldy, Magdalena Mountains, New Mexico, 2001
N
• SAHRA vegetation question: What are the impacts of vegetation change on the basin-scale water balance?
• Today I’ll focus on two issues related to understanding and modeling vegetation hydrologic effects in mountain areas.– Effects of vegetation on hydrologic processes– Mountain Block Recharge (MBR) at hillslope
scale under various conditions, including vegetation types, and vegetation change
SAHRA Scientific Question and My Study
Precip
itation
Bedrock
Soil Soil water
How does water partition on the mountain hillslopes? In particular, what is the percolation across the soil-bedrock interface?
FS
DS
FR
DR
MASTER FAULT
FAULT
OBLIQUEFAULT
Surface Fault Trace
FAULT
Evapotranspiration
?
Precipitation
BedrockInterflow
Percolation
What is the contribution of distributed recharge to mountain-front recharge?
From this percolation, what is the distributed recharge to the mountain block?
Effects of vegetation on hydrologic processes
• Modifies surface albedo
• Intercepts precipitation
• Transpires soil water, actively responds to the atmospheric condition and soil moisture
• Modifies soil
structure
and hydraulic
conductivity
Precip
itation
Bedrock
Soil Soil water
Effects of vegetation on hydrologic processes
We separate these effects into two categories,
– one contributes to the boundary of the model: PE and PT (including Fr, albedo, interception, stomatal resistance, vegetation structure, etc);
– the other contributes to the model parameters: K, root water uptake model.
Hydrologic effects of vegetationNew surface energy partitioning model that we use to separately generate PE and PT on mountain hillslope: SEP4HillET
Hydrologic modeling of the surface and vadose zone: currently HYDRUS
PT PE
Root macropore
Modified from Shuttleworth and Wallace (1985)
SEP4HillET model: Considers effects of the vegetation coverage and slope (aspect and steepness) on surface energy partitioning for ET (E and T separately) modeling
Potential E and T on a shrub-covered surfaceSevilleta NWR, NM (2002), Fr=0.3, LAI=1
0
2
4
6
8
10
1 31 61 91 121 151 181 211 241 271 301 331 361
Julian day
PT
or
PE
(m
m/d
ay)
PT
PEPE=83%, PT=17%
PE=83%, PT=17%
Potential E and T on a grass-covered surfaceSevilleta NWR, NM (2002), Fr=0.55, LAI=1.5
0
2
4
6
8
1 31 61 91 121 151 181 211 241 271 301 331 361
Julian day
PT
or
PE
(m
m/d
ay)
PT
PEPE=60%, PT=40%
PE=60%, PT=40%
The model was tested for estimating both potential evaporation (PE) and potential transpiration (PT) on two surfaces of Sevilleta LTER by comparing to stable isotopic measurements (Boulanger,2003)
Measured: E =79~84%, T = 16~21%Modeled: PE = 83%, PT = 17%
Measured: E = 52~70%, T = 30~48%Modeled: PE = 60%, PT = 40%
Modeled PE and PT
shrub grass
N
Test the hypothesis for distinct vegetation
Different atmospheric demands for ET lead to differentsoil moisture regimes, and support different vegetation.
100 cm soil
30 cm soil
Duration of dry root zone soil
N
Creosote:P/PET ~ 0.18
Boundary P/PET ~ 0.2
Picture from Bruce Harrison
Juniper:P/PET ~ 0.24
Model results with 8-year micrometeological Data at Red Tank station, Sevilleta LTER
Long-term vegetation changes with climate
Mountain Block Recharge (MBR) at hillslope scale
– under various conditions, • including vegetation types, and vegetation change
Precip
itation
Bedrock
Soil Soil water
Granite
Tuff
Granite
Tuff
Annual P=565mmFr=50%
S N S N
Annual P=565mmFr=5%
Percolation: in % of Precip
Aspect effect
4%
4%
31%
17%
Aspect effect
Vegetation control
Soi
l and
bed
rock
ef
fect
s
Generic hillslope hydrologic modeling MBR sensitivity to: bedrock permeability, soil thickness, vegetation
coverage, and slope aspect. (climate variability, rainfall intensity, soil structure change and erosion due to vegetation change not considered)
Soil
Soil
6%
7%
43%
22%
3%
1%
23%
6%
2%
0.3%
16%
1.8%
Los Alamos hillslope experiments(data from Newman, 2003)
Simulations of Los Alamos hillslope experiments
Site description:• ponderosa pine, • 6% slope, • ~ 500 mm annual precip,• permeable tuff
• However, little recharge
Tuff
Simulations of Los Alamos hillslope experiments
Lab measured K
Soil is layered, with lowest measured hydraulic conductivity at 40 cm. However the soil moisture ponds at 60-70 cm. Why?
Tuff
Root
zoneIm
peding layer for percolation
Because of root macropore !
Simulations of Los Alamos hillslope experiments
root zone
tuff
barrier
0
3
6
9
12
Po
ten
tia
l re
ch
arg
e (
cm
/yr)
P=52cm
root zone
tuff
root zone
tuff
0
3
6
9
12 P=52cm Ponderosa
root zone
tuff
0
3
6
9
12 P=38cm
Juniper
Q1: Does ponderosa pine site naturally leads to soil impeding layer?
Q2:Percolation
<?
Los Alamos hillslope experiments(data from Newman, 2003)
Ro
ot
zon
e
Permeable Tuff
Imp
edin
g layer fo
r p
ercolatio
n
Valles Caldera field sites
Hillslope modeling
What controls soil thickness at these sites?
Impeding soil layer?
What is the distributed MBR?
Of the Los Alamos experiments suggests an impeding soil layer below the root zone of ponderosa pine forest. What about Valles Caldera?
Thank you!