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Miguel Erosion in Baja California

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					  Comparison of Satellite and Ground
Vegetation Indexes to Estimate Erosion
in a Mediterranean-climate Watershed




                                                Miguel A. González-Botello
                                                   Stephen H. Bullock and
                                                   J. Mario Salazar Ceseña
                                                            Terrestrial Ecology Lab
                                                 Conservation Biology Department
       Centro de Investigaciones Científicas y de Estudios Superiores de Ensenada
       Introduction             w
       Soil erosion is a natural process that reworks the
       distribution of organic matter, nutrients, and sediments.




       Accelerated erosion is part of the desertification process:
No 2




       loss of productivity, stored carbon and biodiversity
       Introduction
       Soil erosion across a
       5,000 km2 watershed in
       NW Baja California has
       been estimated* using
       the Revised Universal
       Soil Loss Equation
       (RUSLE), in GIS.
No 3




       *Smith, S. V. et al. in press. Soil Erosion and its Potential Significance for Carbon
       Fluxes in a Mountainous Mediterranean-Climate Watershed. Ecological Applications
       Introduction
       In a small area of southern France, DeJong*
       found a weak, linear relation of C to the
       Normalized Difference Vegetation Index (NDVI).

                      C = 0.45 - 0.805 (NDVI)

                                      (NIR – R)
                               NDVI=
                                     (NIR + R)
No 4




       *De Jong, S.M. 1994. Derivation of vegetative variables from a Landsat TM image for
       modelling soil erosion. Earth Surface Processes and Landforms, Vol. 19, 165-178.
       Our objective
       Our project will evaluate the
       relation of C (measured in the field
       with precise methods and large samples
                          to NDVI
       distributed over ~3000 km2)
       and to terrain variables
       (exposure,   slope     and
       elevation) and vegetation
       variables.
No 5
       Study area
       Mediterranean-climate part of Mexico.
       Rainfall of 265 mm
       Between November and April.

       Three Terrestrial Prioritized Regions.
       Chaparral and coastal scrub.
No 6
       Use of GIS in Site Selection
       GIS has been an important
       tool in designing the field
       work and will be essential to
       integration of ground and
       satellite data.

       The location of the field sites
       (c. 67) involved the following
       seven steps:
No 7
       1. Update land use maps
No 8
       2. Exclude non-shrub areas
No 9




       Settled, agricultural and woodland or grassland/meadow areas
        3. Digitize paved and dirt roads
No 10
        4. Create Map of Accessible Areas
        40 and 250 m
        From the roads
No 11
        5. Compare frequency distributions
                 Watershed       Accessible area




             NDVI*           NDVI*
No 12




             ASPECT          ASPECT            * May 2005
        Watershed   Accessible area




         SLOPE        SLOPE
No 13




        ELEVATION    ELEVATION
        6. Select potential field sites
No 14




        Ca. 120 sites. substantially uniform over more than 1 hectare
        regarding slope, exposure and vegetation (visual or NDVI).
        Google Earth Images
        Digital Globe
                                                                  Site selection involved High
                                                                  resolution images of Digital
                                                                  Globe      (Google     Earth),
                                                                  INEGI’s Ortophotos, NDVI,
                                                                  and Slope, Aspect & Height.
        INEGI’s Digital Orthophoto Web Service (WMS)              Slope derived from Inegi’s DEM
        http://antares.inegi.gob.mx/cgi-bin/map4/mapserv_orto?)   On ArcGIS 9
        On ArcGIS 9




        NDVI (May 2005)                                           Aspect derived from Inegi’s DEM
        On ArcGIS 9                                               On ArcGIS 9
No 15
        7. Select among potential sites
        We selected the sites to best represent the
        frequencies from the previous slides.
No 16
        30

        25
                                                                            Sites
        20                                                                  Area




                                                                            Slope
        15

        10

         5

         0
                     5          15            25               35         45              55
                                                   Category

        20




                            Aspect (North)
        18
        16                                                                  Sites
        14                                                                  Area
        12
        10
        8
        6
        4
        2
No 17




        0
              -0.8       -0.6   -0.4   -0.2        0     0.2        0.4   0.6       0.8        1
                                                   Category
             South                                                                    North
        12

        10

        8
             Height                                                                  Sites
                                                                                     Area


        6

        4

        2

        0
             50   200      350    500   650    800     950      1100   1250   1400     1550    1700    1850
                                                     Category




                  NDVI
        25


        20                                                                           Sites
                                                                                     Area
        15


        10


        5
No 18




        0
              0     0.05         0.1    0.15     0.2         0.25      0.3     0.35          0.4      0.45
                                                     Category
        Versatility   With KML’er 1.2, extensive
                      interaction between Google Earth
                      3 and ArcGIS 9 was possible.
No 19
        Field Sampling Method
        Field measurements were
        based on 30 m line transects.

        Drip height, soil surface cover,
        and types of cover were
        recorded at 20 random points
        along the line.
No 20
        Field Sampling Method
        To assess aerial cover, we
        recorded the interception of
        each plant >20 cm diameter
        along the entire transect.

        We also recorded plant species,
        height,   and    perpendicular
        diameter.
No 21
         Field Sampling Method
        Also, to better calibrate
        the erosion model, we
        collected samples of soil
        and litter.

        Terrain variables were
        recorded to compare
        with estimates from the
        digital elevation model.
No 22
        Satellite Image
        Processing
        Landsat data from late April-early
        May 2007 will be processed for
        NDVI (and EVI) and variance
        among years of contrasting
        rainfall will also be analyzed
        (2001, 2003, 2005).
No 23
        Preliminary Results
                                     The major part of sites shows a high soil
                     100%
                                     cover (G Subfactor, 0 – 0.1). This reduces
                     80%             substantially the field calculated C Factor.
        % of sites




                     60%


                     40%                                                                        G Factor (Soil)
                                                                                                H Factor (Drip-height)
                     20%                                                                        P Factor (Vegetation)


                      0%
No 24




                            0.1000   0.2000   0.3000   0.4000     0.5000   0.6000      0.7000     0.8000   0.9000    1.0000
                                                                Subfactor categories
        Preliminary Results
                     60
                                 De Jong Model tend to overestimate
                                 the C factor.
                     50


                     40
        % of sites




                     30

                                                                                        C deJ
                     20
                                                                                        C in field
                     10

                     0
                          0.05   0.1   0.15   0.2      0.25     0.3        0.35   0.4   0.45         0.5
No 25




                                                    Subfactor categories
        Our preliminary results suggests that the deJong
        Model is not suitable to assess erosion in Baja
        California Chaparral and Coastal Scrub.

                  0.4



                  0.3
        C[Jong]




                  0.2


                                                                           y = 0.0266Ln(x) + 0.4303
                  0.1                                                             2
                                                                                 R = 0.2566



                  0.0
No 26




                    0.000   0.005   0.010   0.015          0.020   0.025          0.030         0.035

                                                    C[m]
        Next steps
        Most analyses are pending as field work is
        recently finished.

        The acquisition of 2007 Landsat images are
        in process, the NDVI is not yet available.
No 27
                       Thanks to:


                        2007 Global Scholarship Program



        Conservation
          Program       Centro de Investigaciones Científicas y de
No 28




                            Estudios Superiores de Ensenada

				
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posted:10/19/2012
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