Modelling population changes with years on a network graph
The Sankey diagram would be nicely suited for your problem statement.

The flow width can be the number of refugees migrated, and the end nodes can be the destinations (from and to) of the refugees, and the flow width would be the magnitude of refugee migration.

If you want to model the graph on a geographical map, it can look something like this:



I am not sure whether it can be done in NodeXL or not.  But, a google search has returned me this link.