If I have much lower than normal humidity, how should I change the amount of flour that dough needs?
Do you weigh your flour?  If not, that is the one change that you can make that will make this problem go away.  Most of baking, particularly at the commercial level, is based on ratios by weight.

While there will be some minor differences in the amount of moisture in 10 ounces of flour based on the humidity, how much flour packs into a cup can vary a lot on humidity, how much you've fluffed or sifted the flour first, whether you scoop or sprinkle...you get the idea.

If you don't weigh your flour when you bake, then there are lots of possible problems that could have occurred that may or may not have had anything to do with the humidity.

The only other "seat of the pants" solution is to know your recipe so well that if you notice that there is a problem, you'll catch it early.  Third rise is a little late to be adding moisture, so you would have had to have noticed the problem at the beginning.  

Weighing your flour and water solves many baking problems and makes you look like a pro.

Since you are weighing, then "knowing your recipe and adjusting on the fly" seems to be the only real answer.  I checked around and even Rose Levy Beranbaum says if you weigh, only minor adjustments are needed. In the situation you described I might have added a bit of water at the third rise, then let it have another rise.

Another thought is that, possibly, the air being so dry caused the tops of your rolls to dry out some, so they weren't flexible and you didn't get any oven spring.  A spritz of warm water across the top of the rolls during final rise and, indeed, in the oven (I do it with my sourdough loaves, for instance) helps the bread skin to be loose enough to not inhibit the initial oven spring.