Geoscience Reference
In-Depth Information
Table 8.3
Subpixel imperviousness and land cover class type on the selected 1,219 subwatersheds
that exhibited developed land cover class change between 2001 and 2005
Impervio-
usness
mean
(%)
Standard
devia-
tion.
(%)
Standard
error of
the mean
(%)
Pixel
Count (no.)
Surface
area (%)
NLCD01 class
Open water
682,107
2.1
0.0102
0.6
0.0007
Developed, open space
1,963,787
6.1
7.8431
6.7
0.0048
Developed, low intensity
837,195
2.6
33.1667
10.2
0.0111
Developed, medium intensity
373,067
1.2
63.9875
11.4
0.0187
Developed, high intensity
164,961
0.5
88.5434
7.1
0.0174
Barren land
75,644
0.2
0.2378
4.2
0.0154
Deciduous forest
12,845,925
39.8
0.0016
0.17
0.0000
Evergreen forest
839,736
2.6
0.0023
0.2
0.0002
Mixed forest
422,418
1.3
0.0007
0.1
0.0001
Scrub/shrub
217,332
0.7
0.0104
0.5
0.0010
Grassland/herbaceous
997,511
3.1
0.0068
0.4
0.0004
Pasture/hay
9,138,486
28.3
0.0162
0.7
0.0002
Cultivated crops
3,391,482
10.5
0.0175
1.0
0.0005
Woody wetlands
240,994
0.7
0.0005
0.1
0.0002
Emergent herbaceous wetlands
117,958
0.4
0.0006
0.2
0.0006
The mean percentage imperviousness for the subwatersheds served as a basis
to model TIA based on developed land class counts. For the 2001 data, a com-
parison of both methods was undertaken. TIA was calculated by propagating the
subpixel imperviousness using expression (8.1) and by modeling it with land cover
type by using the conversion factors derived from Table
8.3
. When considering
just the 1,219 subwatersheds, very close agreement was found between estimates
of the total TIA yielded by the two methods, 73,721 and 73,482 ha respectively
(
r
0.999
∗∗∗
; significant at the 0.001 level) (Fig.
8.7
).
=
Fig. 8.7
Total impervious area calculated by two methods - the land cover class model and by
subpixel formula (I); all subwatersheds
