It might well do so - but once the soil under the mulch is moist, it stays moist for a long time - like weeks - and your over-all water consumption should go down considerably.

I mulch my veggies with 3-4 " of grass clippings and the flower beds with 3-4" of bark. Water the veggies every 7-10 days and the flowers every 2 weeks.

David do you let your clippings dry out first?

Something coarse like bark mulch does not absorb a huge amount of water to begin with. It won't take that long for water to soak it and penetrate the soil below - it's not like penetrating 2-3" of garden soil which is extremely absorbent.

Bob_In_Colorado (My Page) on Sat, Jul 12, 14 at 17:36
David do you let your clippings dry out first?

I use fresh and dried and 'forgotten 3 days and started-to-ferment' grass clippings - the fresh are the easiest and most pleasant to spread. They dry pretty quickly once they're spread as mulch.

I use untreated western red cedar in all of my beds. Keep it a couple of inches away from the base of the plant; the water will easily get in right where you want it to and you won't have the issues that come with wet wood snuggling up to greenery. I'm sure 2" would be plenty, especially with cedar since it mats so well.
Good luck!

I second what amester said--make sure to give your veggie plants a few inches where the mulch is pulled back, and you should be fine. Ideally, you might consider switching to a drip irrigation under the mulch if you like how it works for you.

We use shredded leaves, and lots of them. To them we add fresh grass clippings on top, which dry out very quickly. Then in the fall we add more leaves and till everything in, along with llama poo.

Keeps the soil cooler and almost always moist. With our weird weather this year, I've watered the tomatoes twice this summer - so far.