Geog. 143 -- Global Environmental Change

Exercise 6:  Land-Cover Change

The illustration of global land-use/land-cover change over the past several decades is facilitated by two things:  1) satellite remote-sensing images, in particular those from the Landsat series of satellites; and 2) the rapid pace of change, which allows images recorded just a few years apart to register considerable change.

This exercise makes use of a web-browser interface to the paired "before/after" images that appear throughout One Planet Many People, and allows locations to be selected either through a list or via a Google Maps display.

The web page is called Atlas of Our Changing Environment on Google Maps, and is at:

http://na.unep.net/digital_atlas2/google.php

There are two ways to select an image pair for viewing:  1) using the Google Maps interface, and clicking on one of the UNEP icons, or 2) using the scrolling list on the right-hand side of the page.  The list presents sites in alphabetical order, and can be sorted in different ways.

To see how the interface works, open the images for the Everglades, either by clicking on the icon over Florida, or scrolling through the alphabetical list, and clicking on "Everglades."  After clicking on either the icon or name, a small two-panel window will pop up.  Clicking on the "View detailed site information" link in the small window will open a new page with enlarged versions of the two (before and after) images.  The images may be further enlarged by clicking on either of the images, or the "View Large Image" links.  Beneath the image is a "story" about the particular land-cover change being illustrated and its causes, as well as some additional, usually land-based photographs.  This page can be closed in the usual way when you're done with it.

(Note that if Google Earth is installed on the machine you're using (not always a safe assumption), you can also view the images in Google Earth by clicking on that link.  You'll have to use the "Places" hierarchy to select the individual images.)

Back on the main Atlas web page, the pop-up window can be closed using the small "X" button in the upper right-hand corner or by clicking on another icon or image title.  A couple of hints:  1) clicking on the "Full Extent" button (lower right corner of the Atlas screen) will zoom the map back to its original extent; 2) sometimes it will be helpful to reload the main page using the "Reload current page" button on the browser tool bar.

As is the case with images in general, the examination and interpretation of the changes recorded by the image pairs might be done hierarchically, from general large-scale features, to specific smaller-scale ones; for example:

  • What is the most evident, large-scale change between the images (i.e., what's the most noticeable difference between the images)?

  • In the areas of greatest change, what are the details of the change?  (What land-cover type was replace by what new type?)

  • What are the most noticeable second-order changes?  (Are there smaller areas with clear changes?  What else is going on in the image pairs?)

  • Are there finer-grain changes that are evident  (e.g. changes that don't appear in as distinct patches but instead as diffuse changes in appearance)?

1.  The Everglades (Urbanization)

Examine the Everglades image pair (reopening it if necessary).  Note that each image in the pair has a zoomed-in inset of an area near Ft. Lauderdale.  South Florida has been one of the most rapidly urbanizing areas in the U.S., with built-up areas expanding at the expense of cropland and the native wet grassland known as the Everglades.

Q1:  Noting that the images were recorded at different times of the year, and so there will inevitably be some difference in color (i.e. ignore the red stuff near the top of the image), what is the main difference in land cover between images?  What is the likely impact this change has had on surface-water hydrology?  Why do so many of the large patches on the images have sharp edges and angular shapes?

2.  Las Vegas (Urbanization and Hydrological Change)

The growth of Las Vegas provides another example of the intersection of urbanization and the environment.  The areal scope of the land-cover change can be noted in the 2006 image via the blue-shaded grid of lines formed by arterial streets spaced 1 mile apart.

Q2:  The 1973 image clearly shows the presence of alluvial fans along the edges of the mountains that flank the basin Las Vegas is in.  What proportion of the 2006 urbanized area is built on alluvial fans, and what are the implications of building on such landforms?  As Las Vegas expanded, what landforms are the ones least affected by urbanization?

3.  Larson Ice Shelf (Cryospheric Change and Global Warming)

The rapid "calving" (or disintegration) of the Larson Ice Shelf in Antarctica was in the news a few years ago owing to the unusually large size of the floating ice shelf that was involved, and the plausibility of the connection to global climate change.  The paired images, and the sequence of images on the bottom of the page show what happened.  Note that there are actually three ice sheets involved:  Larson A, which broke up before these images were recorded, Larson B, the large one that broke up between the times the images were recorded, and Larson C, which can be seen disintegrating at the bottom of the sequence of images.

Q3:  Looking at the paired images, as well as the sequence of images, how do ice shelves break up?  Do they disintegrate into small pieces and then disappear?  Do relatively large areas break off nearly intact, and then disintegrate?  Speculate on the relative roles of sea-level rise vs. local climate change on the particular style of the break up.

4.  Your Choice

Pick an interesting image pair.

Q4:  Describe the changes recorded by the images, and discuss what the proximate (close in) and ultimate (e.g. global) controls are.;