Background

In portions of Arizona and Mexico, the months from April to June are characterized by extreme dryness. This period usually ends abruptly with the onset of summer rainfall and thunderstorms, known as the monsoon.

Objectives

Use the RangeView website to . . .
     1) Choose appropriate images for viewing precipitation effects on greenness.
     2) Identify the start of the monsoon in 1999 and 2000
     3) Determine the relationship between greenness and precipitation as seen in satellite imagery

Tools

This exercise uses the AVHRR Dynamic Animation Tool (link opens in separate window).

To find the tool without the direct link:
     1) In your Internet browser, go to http://rangeview.arizona.edu.
     2) Click on “Dynamic Animation with AVHRR Data ” in the Tools section on the home page.

Exercise

Objective 1: Choosing an appropriate image type

1. Choose "Arizona" from the “Zoom To” menu at the top of the screen. Wait a few seconds for the images to reload.

2. Select both the layer and label checkboxes next to "Major Cities" in the layer list on the left side of the screen. Click the "Refresh" button below the map images.

3. Select the “Zoom in” radio button at the top of the screen, and click once on Tucson to zoom in closer.

4. Choose a data type from the menus below each viewer that will highlight the effect of precipitation on vegetation greenness and allow you to compare Arizona’s monsoon seasons for 1999 and 2000. The available image types are:

   • Greenness (NDVI): shows vegetation greenness and can be used to compare greenness from one place to another.
   • Difference from Average NDVI: shows whether an area is more (orange) or less (blue) green than average.
   • Difference from Last Year's NDVI: shows whether an area has more (orange) or less (blue) greenness than last year
   • Difference from Last Period's NDVI: shows whether an area has increased (orange) or decreased (blue) in greenness from one period to the next.
     
     
5. Select the same year for both viewers to look at the monsoon seasons one at a time, or select a different year for each viewer to compare the monsoon seasons.
6. Click "Animate" to create a timeseries of images.

Objective 2: Identifying the beginning of the monsoon

Compare Arizona’s monsoon seasons for 1999 and 2000. Note that the monsoon usually falls between June 15 and September 30.

Below are some questions to consider. Your animation may not be able to address all of the questions. If it can not answer the question, think about why it can not.

When do you think the monsoon started – at the beginning, middle, or end of which month?
1999    2000

Which year had the most rain during the monsoon season?

Is this a normal amount of rain for this season?1999    2000

How significant is the monsoon’s effect on vegetation greenness over several months?

Objective 3: Vegetation greenness and precipitation

Does this correspond with what you predicted?

Look at the amount of rainfall for each month. In which month do you expect to see the highest vegetation greenness values?
1999?    2000?

Look at the animations again. Does there appear to be a lag in the effects of precipitation on vegetation greenness?