2010-06
46(3)
北京师范大学学报(自然科学版)
Journal of Beijing Normal
Univ
巳
rsity
(Natural Science)
245
MATCHING
XINANJIANG
MODEL
AND
TOPMODEL
FOR
DESCRIBING SPATIAL
SOIL
MOISTURE
PATTERNS
OVER
THE
CATCH
岛
1ENT
头
ZHOU
Maichun
l)
GAO
Yongtong
2
)
LIU
Yuan
l)
(
1)
College
of
Water
Co
nservancy
and
Civil
Engineering
,
South
China
Agricultural
University
,
510642
,
Guangzhou
,
China;
2)
Library
,
So
uth
China
Agricultural
University
,
510642
,
Guangzhou
,
China)
At
陪
tract
The modified Xinanjiang model uses a double parabolic curve to represent spatial distribution of soil
moisture storage capacity over a catchment for runoff generatio
n.
The double parabolic curve has a built-in structure,
which
is
able to simultaneously describe multiple soil moisture patterns co-existing over the catchment. However, it
is
in
a statistically integral form
and
is
usually obtained by optimal calibration using observed rainfall runoff data.
The
wetness
index or the
soil-topographic
index, proposed in the classical TOPMODEL, predicts the individual point soil moisture.
The simplified assumptions
of
steady state for the whole catchment and the water table parallel to the surface, however,
prevent the TOPMODEL applicable to every point in the catchment.
By
matching the double parabolic curve and the
wetness index
, both rainfall runoff data and the distributed topographic data are fully used. The spatial distribution of
different behaviour zones of soil moisture
is
identified over a specific catchment.
The
threshold
of
wetness index for the
definition of applicable region of TOPMODEL
is
identified
in
the catchment.
Key
words double parabolic curve; wetness index; soil moisture; Xinanjiang model; TOPMODEL
Topography
controls
water
movement
velocity
,
convergence
and.
divergence
over
surface
through
slope
direction
and
gradient.
As
results
of
runoff
flux
,
high
soil
erosion
often
occurs
along
the
main
drainage
path
and
above
midslope
positions
,
whereas
high
deposition
takes
place
towards
the
bottom
of
the
catchment
and
in
the
main
drainage
path
immediately
below
zones
of
high
erosion.
Correspondingly
,
soil
is
shallow
,
more
compacted
,
and
tend
to
be
drier
where
ridges
are
located
,
and
deep
,
less
compacted
and
wetter
around
channels
and
in
convergent
areas.
In
the
surface
soil
,
A-horizon
depth
increases
and
the
gravel
content
decreases
downslope.
The
saturated
hydraulic
conductivity
in
the
upper
slopes
is
much
higher
than
in
the
lower
parts.
Soil
moisture
distribution
shows
a
high
degree
of
organization
Csystematic
variation
or
consistent
patterns)
in
space
and
time
[l
J.
These
patterns
overlay
the
whole
catchment
according
to
topographic
positions
such
that
no
distinct
divide
between
them
can
be
easily
identified.
On
the
other
hand
,
factors
affecting
soil
water
movement
involve
not
only
topography
but
also
soil
property
according
to
Darcy'
s
law.
Topography
determines
the
elevation
component
of
soil
moisture
potential
gradient
,
both
at
saturation
and
when
not
saturated.
Soil
property
determines
parameters
of
soil
moisture
movement
such
as
infiltration
rate
,
saturated
or
unsaturated
hydraulic
conductivity
,
capillary
fringe
,
soil
suction
when
not
saturated
,
etc.
The
collection
of
distributed
data
on
soil
attributes
,
however
,
is
difficult
or
very
tim
e-
consuming.
The
ready
availability
of
digital
elevation
models
CDE
肌
1s)
or
topographic
maps
with
a
high
accuracy
has
led
many
researchers
in
the
past
four
decades
to
explore
the
close
linkage
between
the
distribution
of
soil
attributes
and
the
topographic
features.
Among
different
topographic
variables
,
the
wetness
index
has
been
studied
most
intensively
and
祷华南农业大学校长科学基金资助项目
(7600-K07050)
;广东省教育厅高等学校人才引进专项资金资助项目(粤教师
[2008J86
号)
;广东省水利
科技创新资助项目
(2009)
收稿日期:
2009-12-15