Julie,

Your Variegated Norway Maple is short of water. The evidence for that, in addition to the numerous fallen leaves, are on the leaves in all the images, and is especially obvious in the 2nd image. Wherever the leaves have developed dry brown areas, it means that those tissues are dead.

This year, numerous trees and other plants are having a tough time because natural rainfall has been very scanty. Add to that the recent ongoing heat wave, and you have trees in crisis.

Maples, and many other landscape trees, and especially fruit trees, require deep watering every 2 to 3 weeks through our dry summer months.

Your tree is in an elevated planter which, I presume, is where you have been watering it.

Even so, it's very likely that the roots have escaped that very limited planting space and have grown outward to a foot or more beyond the dripline. (The dripline is an imaginary line on the ground at the tips of the branches.)

Critical factors when irrigating a tree:

• The most effective place to irrigate trees is the entire area underneath the canopy, plus 1 to 2 feet beyond.
  
• The goal is to moisten the soil to at least 12 inches deep.
• Irrigate thoroughly every 2 to 3 weeks during the dry summer months.
  

Next, do a test-run to determine how long to irrigate to moisten the soil to at least 12 inches deep.

• Run the sprinkler system (or a hose-end sprinkler) for a total of one hour runtime. (To avoid runoff, run several  on-off cycles.)
  
• After the tree has been irrigated for an hour, turn off the system for an hour.
  
• Probe the irrigated soil with a long flat-head screwdriver (or a trowel) to know how deep the moisture penetrated. (The probe will stop when it hits dry soil, a root, or a rock; if penetration is too shallow, try again several inches farther away.)
  

If the soil is moist to 12 inches deep, run the system for an hour every two weeks; if the soil is moist to only 6 inches, run time is 2 hours; etc.