It works the other way around. Mulch prevents evaporation and provides shade to the soil. Those effects keep more moisture in the soil and keep it cooler in the summer. Besides that, if you are watering a full inch once a month or so this time of year, the water will flow right through the mulch.

Start with moist soil before you apply the mulch, and put a soaker hose (the round ones that ooze water) snaked around the bushes under the mulch for those times when they need more water.

I would think that's right, that mulch inhibits water penetration, in that it takes a certain amount of water to just get the mulch wet, and more water is needed to actually penetrate into the soil. But, as noted, mulch prevents water from going both ways. That is, once the soil underneath is moist, mulch will prevent it from drying out.

One strategy is just to water heavily after the mulch is first put down. Sample the soil to assess penetration. When the soil is moist to depth, water lightly from then on.

If I were you, I wouldn't follow any particular recipe of inches per month until you figure out what you really need. I would gently dig in one spot, once a month, and see if you're watering enough. Get to know your own soil.

Mulches can keep moisture from penetrating to the soil although mulches do aid in soil moisture retention, it depends on how and for how long the overhead water is applied. Many people put soaker hoses under the mulch to ensure moisture gets to the plants.

Mulch will do more for your plants than not mulching will.

kimmq is kimmsr

There is a Arizona gardener named VeganAthlete that puts out youtube videos about gardening in the desert. He uses a heavy wood mulch to hold moisture in. You should check out his videoes.