APPENDIX S5 – Sierra San Miguelito: Land-cover classification and land use
change assessment at the regional scale
We used GIS (Geographical Information Systems) to assess plant cover with the
processing of spectral images. With this technique of remote sensing we generated
thematic maps that allowed us to identify land use type as well as cover changes
between 1979, 1989, 1999 and 2009. To generate these maps we used a combination
of supervised and unsupervised Landsat satellite images from 1979, 1989, 1999 y
2009.
The Landsat images were obtained from the USGS (United States Geological Survey)
[1]. To analyze the images we used GRASS-GIS (Geographic Resources Analysis
Support System, v6.4.2 RC3) software; for the unsupervised classification we
implemented the MLC (Maximum Likelihood Classifier) algorithm, and for the
supervised classification we used SMAP (Sequential Maximum A Posteriori
Classifier) algorithm [2, 3]. Steps for the unsupervised classification included: wave
grouping in the Landsat image per decade, cluster formation for spatial statistics using
20 classes (pixel signatures) and cluster classification with the MLC algorithm. Steps
for the supervised classification included wave grouping in the Landsat image per
decade, generation of training areas, cluster formation with 8 plant cover types, and
cluster classification with the SMAP algorithm.
To estimate land cover changes within the study site, the area was estimated for each
land use type, for each of the four years. We used altitude isoclines (2150 m a.s.l. to
the E and 1900 m a.s.l. to the S and N) to delimit the study site, using the elevation
digital model for the site (USGS, 2011, figure S5.1).
Scenario - We simulated how loss of soil depth (key slow variable) (from 30 to 20
cm) observed in the Amapola landscape as a consequence of forest to grassland
conversion, may have triggered regional changes in dryland hydrological function in
the Sierra San Miguelito [4].
Biogeochemical model description - We parameterized the biogeochemical model
BIOME-BGC [5], which is a mechanistic model to simulate pools and fluxes of C, N
and water in vegetation and soils of terrestrial ecosystems [5, 6]. Values for the
parameters were derived from previous studies in the area, including forest
productivity [7], forest C and N pools [8, 9] and forest hydrology [10, 11]. The model
was run over satellite images from Sierra San Miguelito, SLP, Mexico (figure S5.1).
We ran the model for a 30-year period (1979 to 2009) to simulate water fluxes in the
form of total evapotranspiration (ET) and runoff by type of plant vegetation cover.
This simulation was run under current soil conditions of 30 cm average soil depth
(figure S5.2). The output consisted of decadal (1979, 1989, 1999 and 2009) averages
of ET and runoff by plant cover type. A second run was applied to examine scenarios
of soil erosion including a 10 cm soil loss (figure S5.3) and compared to current
values. Also, interannual variability of air temperature and precipitation for the 30year simulation [12] is presented in figure S5.2. Outputs of the model were
superimposed on thematic maps including the most characteristic land cover types, so
estimates of hydrological responses could be made at the regional scale (figure S5.3).
Area (ha)
Land Use Change
50000
45000
40000
35000
30000
25000
20000
15000
10000
5000
0
Forest
Chaparral
Grassland
Cropland
Dams/urban
1979
1989
1999
2009
Figure S5.1: Land cover/use change in the Sierra San Miguelito, San Luis Potosi,
Mexico between 1979, 1989, 1999 and 2009 using false color satellite images.
Annual total Evapotranspiration 1979-2009, 30 cm soil depth
1000
18
900
Rain/year
Forest
Chaparral
Grassland
Temp/avg
800
17
600
16
500
16
400
15
300
200
15
100
14
0
Temperature (°C)
17
700
ET (mm/yr)
18
14
1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
year
Annual total Outflow1979-2009, 30 cm soil depth
1000
Rain/year
Forest
Chaparral
Grassland
Temp/avg
Outflow (mm/yr)
800
18
18
17
700
17
600
16
500
16
400
15
300
200
15
100
14
0
14
1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
year
Figure S5.2: Annual evapotranspiration (top) and outflow (runoff) (bottom) in relation
to annual precipitation and mean annual temperature between 1979 and 2009 for three
land use types in Sierra San Miguelito, San Luis Potosi, Mexico.
Temperature (°C)
900
200000
100000
0
250000
200000
150000
100000
50000
0
1989
1999
1989
1999
300000
300000
200000
200000
100000
100000
0
2009
Total outflow 1979-2009 /20 cm soil depth
1979
Total ET 1979-2009
cm soil depth
Total ET 1979-2009
/30 cm soil/30
depth
400000
2009
0
1979
250000
200000
150000
100000
50000
0
M mm/study area
Mmm/study area
1979
400000
M mm/study area
300000
M mm/study area
Total ET 1979-2009 / 20 cm soil depth
M mm/study area
M mm/study area
400000
1979
1989
1989
1999
1999
2009
2009
Total
outflow 1979-2009
30 cm soil depth
Total outflow
1979-2009
/ 30 cm soil/ depth
250000
200000
150000
100000
50000
0
1979
1979
1989
1989
1999
1999
2009
Figure S5.3: Outputs of Biome-BGC for total evapotranspiration (top) and surface
runoff (bottom) for three land use types (grassland-yellow, chaparral-light green,
forest-dark green) in the geographic region of Sierra San Miguelito, between 1979
and 2009. Simulations are presented for soil erosion scenarios with 30 cm soil depth
(left side) and 20 cm soil depth (right side).
2009
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