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Net Precipitation
Net Precipitation= This is the amount of water reaching the mineral soil
Pg-It
Pg=precipitation It=total interception
Interception & Net Precipitation
Interception= the removal of water from precipitation by
living or dead vegetation (and then evaporation) before it reaches the mineral soil
(stored on vegetation and lost as
evaporation from vegetation during
or after storm)
It=Ic+Il
It=total interception
Ic=canopy interception
Il=litter interception
Interception & Net Precipitation
Canopy Interception 10-20% lost due to interception (varies due to
stand characteristics and climate)
Forest Floor Interception 1-5% and depends on thickness of litter, water
holding capacity, frequency of wetting, and
evaporation rate.
Interception & Net Precipitation
Interception increase with time
1) Interception increases during storm event and
then levels off
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0 20 40 60 80 100 120
# min. since storm start
"Inter. Storage
Capacity
Canopy Interception
Ic=Pg-Th-Sf
Pg=Total Precipitation
Th=Throughfall
Sf=Stemflow ---describe each----
Interception & Net Precipitation
Water not intercepted by canopy
1) throughfall- precipitation passing through
canopy or dripping from a canopy
2) stemflow- water passing from the canopy,
down the stem to the soil
Factors Effecting Interception
Storm Factors
-Interception loss is greater for rain than snow
-Low intensity, long duration storms have more
interception loss due to greater evaporation of
interception during the rainstorm
-Short duration storms with windy conditions
decrease interception due to movement of foliage
etc.
Factors Effecting Interception
Storm Factors
-Interception loss is greater for rain than snow
Factors Effecting Interception
Climatic Conditions -Higher humidity less evaporation & thus
interception
-Vegetation temperature, higher temperature
more evaporation & interception
Factors Effecting Interception
Climatic Conditions Interception can be an increase in net
precipitation in humid areas where foliage
intercepts fog which condenses and drips to soil
Factors Effecting Interception
Vegetation -Interception increases with increasing leaf area thus
a) interception increases with age/species
b) denser stands have more interception
c) during the dormant season
hardwoods have less interception
d) forest floor interception increases with
density, age, slow decomposition
Factors Effecting Interception
Tree Species (Density/Species)
Basal Area
(m2/ha)
%
Interception
Longleaf 20.9 12.4
Shortleaf 39.5 18.5
Loblolly 37.9 15.5
Slash 36.2 16.8
Factors Effecting Interception
Age (White pine stands)
If=1.27N +0.08 Pg (10 year old stands)
If=1.27N+0.12 Pg (35 year old stands)
If=1.52N+0.18 Pg (60 year old stands)
N=# storms
Pg=Precipitation “
Factors Effecting Interception
Age Forest Floor Int.
Factors Effecting Interception
Vegetation -Interception increases with increasing layers of vegetation (canopy structure)
Factors Effecting Interception
Vegetation -Interception increases with increasing layers of vegetation (canopy structure)
Factors Effecting Interception
Vegetation Type
Conifers =0.03-6.6mm
Hardwoods=0.3-2.0 mm
Shrubs=0.3-2.0mm
Grass=1.0-1.5mm
Factors Effecting Interception
Vegetation -Interception is altered by vegetation physiology
a) Waxy leaves have less interception
b) Smooth bark decreases interception due
an increase in water movement on bark and
an increase in stemflow
c) Needle shape and the greater leaf
area of conifers increases interception
Factors Effecting Interception
Interception Loss—10-40% of precipitation Stemflow <2-3% of precipitation Throughfall 96-99% of precipitation
Precipitation, Throughfall, & Stemflow in
Pines & Pine/Hardwoods Ouachita Mtns.
0
10
20
30
40
50
60
PREC Tf PINE Sf PINETf P/H Sf P/H
Redistribution of Water By Vegetation
Types of vegetation determines stemflow , throughfall, & canopy drip -Pendulous branches: favor canopy drip -Erect of acute branches: favor stemflow
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