My theory.

[tonka]

I am about as green as they come with the vast knowledge to be had about maple syrup and the production of it. Last season there were reports of very high sugar content and I experienced it my self since I had only 200 taps out and yielded 85 gallons of the final product. I don't mean to sound arrogant when I say this but my theory is the drier the prior summer was the higher the sugar content is, has there been any research done on what affects high and low sugar content no matter the maple species?

[Michael Greer]

All theories are viable until disproven. It make some sense that the leaves are doing their work in either case, dry or wet, within reason. (In super dry years the leaves may even wither and drop prematurely, but that's not what you're talking about.) Anyway, the leaves are using sunlight to make sugars, and the sugars get stowed somewhere, and maybe there's less water stored away, so...maybe so. If you're a record keeping sort of person, it should only take ten or fifteen years to begin to notice a pattern, which may or may not confirm your hunch.
If you're right though, how will we stop the rain?