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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 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


Introduction Estimate Erosion in a Mediterranean-climate Watershed

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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


Introduction Estimate Erosion in a Mediterranean-climate Watershed

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


Introduction Estimate Erosion in a Mediterranean-climate Watershed

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.


Our objective Estimate Erosion in a Mediterranean-climate Watershed

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.


Study area Estimate Erosion in a Mediterranean-climate Watershed

Mediterranean-climate part of Mexico.

Rainfall of 265 mm

Between November and April.

Three Terrestrial Prioritized Regions.

Chaparral and coastal scrub.


Use of GIS in Site Selection Estimate Erosion in a Mediterranean-climate Watershed

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:


1. Update land use maps Estimate Erosion in a Mediterranean-climate Watershed


2. Exclude non-shrub areas Estimate Erosion in a Mediterranean-climate Watershed

Settled, agricultural and woodland or grassland/meadow areas


3. Digitize paved and dirt roads Estimate Erosion in a Mediterranean-climate Watershed


4. Create Map of Accessible Areas Estimate Erosion in a Mediterranean-climate Watershed

40 and 250 m

From the roads


5. Compare frequency distributions Estimate Erosion in a Mediterranean-climate Watershed

Watershed

Accessible area

NDVI*

NDVI*

* May 2005

ASPECT

ASPECT


Watershed Estimate Erosion in a Mediterranean-climate Watershed

Accessible area

SLOPE

SLOPE

ELEVATION

ELEVATION


6. Select potential field sites Estimate Erosion in a Mediterranean-climate Watershed

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


Google Earth Images Estimate Erosion in a Mediterranean-climate Watershed

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


7. Select among potential sites Estimate Erosion in a Mediterranean-climate Watershed

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


Slope Estimate Erosion in a Mediterranean-climate Watershed

Aspect (North)

South

North


Height Estimate Erosion in a Mediterranean-climate Watershed

NDVI


Versatility Estimate Erosion in a Mediterranean-climate Watershed

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


Field Sampling Method Estimate Erosion in a Mediterranean-climate Watershed

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.


Field Sampling Method Estimate Erosion in a Mediterranean-climate Watershed

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.


Field Sampling Method Estimate Erosion in a Mediterranean-climate Watershed

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.


Satellite Image Estimate Erosion in a Mediterranean-climate Watershed

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).


Preliminary Results Estimate Erosion in a Mediterranean-climate Watershed

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


Preliminary Results Estimate Erosion in a Mediterranean-climate Watershed

De Jong Model tend to overestimate the C factor.


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


Next steps not suitable to assess erosion in Baja California Chaparral and Coastal Scrub.

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.


Thanks to: not suitable to assess erosion in Baja California Chaparral and Coastal Scrub.

2007 Global Scholarship Program

ConservationProgram

Centro de Investigaciones Científicas y de Estudios Superiores de Ensenada


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