How To: Find Change in Elevation Over Time

To find the change in elevation you must calculate the difference in volume between two DEMs (one for each year in question, ie. 2003 vs 2010)

  1. Subtract one DEM from the other: ArcToolbox --> 3D Analyst Tools --> Raster Math --> Minus
  2. Input raster or constant value 1: select your oldest DEM
  3. Input raster or constant value 2: select your newest DEM
  4. Output raster: create a subfolder within your working folder. -- OK 
Note: Elevation values are now represented as such: 0 equals no change, positive values represent amount of increase in elevation (ie. valley fill), and negative values represent amount of decrease in elevation (ie. MTR)

Just to visualize the difference, you could create a Hillshade/Shaded Relief of the your DEMs.

Our goal now is to calculate the amount of increase vs the amount of decrease in elevation

  1. ArcToolbox --> 3D Analyst Tools --> Functional Surface --> Surface volume.Drag in the new DEM, created in step 1.
  2. Create a subfolder within your working folder for this file and specify a name (saves as an ASCII text file). 
  3. Reference Plane to : set to ABOVE to calculate increase in elevation 
  4. Set Plane Height to 0 
  5. Z Factor: leave as default (1) - OK 
  6. To calculate the decrease in elevation repeat steps 1 through 5, this time choosing BELOW for the Reference Plane.
The txt files will appear in the Table of Contents (you may need to select the “List by Source” icon in the Table of Contents to see it listed under Layers). Right click to open the file. The volume of change will be displayed in the same units as your DEMs.
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