I've used Tundra to represent the Rann of Kutch seasonal salt marsh (see: http://www.nationalgeographic.com/wildworld/profiles/terrestrial/im/im0901.html).
If you are short of terrain types, I imagine you might want to use this salt marsh or the mangrove/swamp terrain type since they're used the least. I'm not sure what to change it to though. You can use the link I gave to figure that out for yourself. The rest of that site might also be useful, since it can provide background info about the rest of the map too.
You can find an interactive world map here: http://www.nationalgeographic.com/wildworld/terrestrial.html
And a list of "ecoregion" profiles:
http://www.nationalgeographic.com/wildworld/profiles/terrestrial_im.html

The Forest terrain type has been used for "Dry Forest", Jungle for "Rain Forest" and Swamp for "Mangrove". The dry forest is still mostly (sub)tropical, so it will need more appropriate graphics.

You will probably also want to make slight adjustments to the terrain to fit the cities, e.g. when they'd end up in the middle of the mountains or jungle. I don't know how scenario designers usually do that, so I just mention it to be sure.
