Can I see how these cities have lost elevation using digital elevation models? Is there a digital elevation model which data are updated? Or are there other methods?
If I understand correctly what you're asking, you want to see what has changed between two DEMs from two seperate time periods. Assuming that these two datasets have the same resolution you would want to use the minus tool (you need to have spatial analysis licensed) and that will give you the difference between the pixels in each data set. So if one pixel has a value 1454m at one data and the corresponding pixel from a later date with an elevation of 1450m a raster would be created that has a pixel value of -4m.