Sizing cables in pulsed power applications
You know the temperature rise just like every other wire...Max Insulation Temp - Maximum Ambient Temp.

Calculating temperature rise due to pulses would require things like thermal impedance if you go with the physical models and those are basically simulations. 2000A is a lot of current so will produce a lot of resistive voltage drop in your wire so try this first instead...it's much easier:


Determine your allowable voltage drop.
Determine the resistance required to achieve this.
Find an AWG with this resistance.
Check a standard table to see if that AWG can't already support 2000A continuously. If it can, you're done (although it still might be tough to find a table with AWGs that can go up to 2000A).