RESULTS

"The occurrence of less or more rainfall worldwide due to El Niño has an important impact in the world's climate. Sometimes environmental changes are severe, mainly in regions where drought occurs. During 1997 and a part of 1998, Australia, Indonesia, Brazil and Mexico, among other countries, experienced one of the most severe drought periods in the last years" (Conde et al; 1999:132). The states of Michoacán, Jalisco and Guanajuato reported minimum rainfall (0 milimeters) in April, 1998. As a result, a decrease in the surface of water bodies and forests was recorded for that year.

The analysis´ results are reflected in a matrix of changes, where rows correspond to classes of the 1993 image and colums correspond to classes of the 1998 image. Shaded squares represent the percentage of coverage without changes.

MATRIX OF CHANGES 1993 - 1998

(values expressed in percentage)

According to the matrix, the classes which experienced the greatest change were grassland, bodies of water and mosaic. 93% of the grassland was classified as agriculture; 29% of the bodies of water was classified as areas without vegetation; because of the decrease in the level of water, soil appears without vegetation. Classes recording an increase were agriculture and areas without vegetation.

Here are three examples of zones where vegetation changes were detected, along with two animations.

Ejemple 1

Site: Misterio de Chorro hill, 28 km north of Irapuato city in Guanajuato. The forest class recorded a decrease, being substituted by the mosaic class. It should be noted that meteorological conditions prevailing in 1998 may have well produced dry vegetation and thus a different spectral response, producing an apparent decrease in vegetation.

Ejemple 2

Site: Northwest of Pátzcuaro Lake in Michoacán. Drought conditions during 1998 favored a greater occurrence of fires as compared to other years; according to information provided by the SEMARNAP, Michoacán was classified as one in ten states with more fires in forest areas. An example of the effects of these fires appears in the 1998 image.

Ejemple 3

Site: Near to Purépero de Echaiz. We observe a decrease in forests, detecting burnt areas.

Animations

This animation is only a transition -in form and color- from the 1993 original image to the 1998 final image, therefore, it does not provide information about years between these dates.

For this animation, Landsat TM satellite images recorded in April, 1993 and 1998 were used. Each image was overlaid on a digital elevation model. This classification was the basis for a virtual view of the area, defining an ecosystem mainly with trees and bushes for each class, with Onyx Tree and WCS software.

The water level dramatically decreased in 1998 as a consequence of El Niño, as can be observed in lakes Cuitzeo and Pátzcuaro.

Cuitzeo Lake (animation)

Original image 1993

Final image 1998

Pátzcuaro Lake (animation)

Home page | Michoacán Case | Guerrero Case | Valle de Bravo Case | Naturale desasters casoe Hurricane Pauline

For doubts, questions or comments
Geographical Information Systems Sub-director