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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

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Miguel A. González-Botello Stephen H. Bullock and J. Mario Salazar Ceseña

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Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

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


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

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: loss of productivity, stored carbon and biodiversity


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

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.

*Smith, S. V. et al. in press. Soil Erosion and its Potential Significance for Carbon Fluxes in a Mountainous Mediterranean-Climate Watershed. Ecological Applications


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

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)

(NIR + R)

NDVI=

*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.


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

Our objective

Our project will evaluate the relation of C (measured in the field with precise methods and large samples distributed over ~3000 km2) to NDVI and to terrain variables (exposure, slope and elevation) and vegetation variables.


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

Study area

Mediterranean-climate part of Mexico.

Rainfall of 265 mm

Between November and April.

Three Terrestrial Prioritized Regions.

Chaparral and coastal scrub.


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

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:


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

1.Update land use maps


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

2.Exclude non-shrub areas

Settled, agricultural and woodland or grassland/meadow areas


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

3.Digitize paved and dirt roads


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

4.Create Map of Accessible Areas

40 and 250 m

From the roads


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

5.Compare frequency distributions

Watershed

Accessible area

NDVI*

NDVI*

* May 2005

ASPECT

ASPECT


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

Watershed

Accessible area

SLOPE

SLOPE

ELEVATION

ELEVATION


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

6.Select potential field sites

Ca. 120 sites. substantially uniform over more than 1 hectare regarding slope, exposure and vegetation (visual or NDVI).


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

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)

http://antares.inegi.gob.mx/cgi-bin/map4/mapserv_orto?)

On ArcGIS 9

Slope derived from Inegi’s DEM

On ArcGIS 9

NDVI (May 2005)

On ArcGIS 9

Aspect derived from Inegi’s DEM

On ArcGIS 9


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

7.Select among potential sites

We selected the sites to best represent the frequencies from the previous slides.


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

Slope

Aspect (North)

South

North


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

Height

NDVI


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

Versatility

With KML’er 1.2, extensive interaction between Google Earth 3 and ArcGIS 9 was possible.


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

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.


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

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.


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

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.


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

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).


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

Preliminary Results

The major part of sites shows a high soil cover (G Subfactor, 0 – 0.1). This reduces substantially the field calculated C Factor.


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

Preliminary Results

De Jong Model tend to overestimate the C factor.


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

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


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

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.


Miguel a gonz lez botello stephen h bullock and j mario salazar cese a

Thanks to:

2007 Global Scholarship Program

ConservationProgram

Centro de Investigaciones Científicas y de Estudios Superiores de Ensenada


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