The ongoing drought of the past decade or so has depleted soil moisture to the level that trees and shrubs are being stressed. Leaves are falling from some aspens; some branches are turning yellow, as are some whole trees. Needles and some branches on pines are turning red, well ahead of the normal needle-cast of fall.
Probably the best and most water-efficient way to relieve trees and shrubs is to use an injector. It has a 2-foot metal tube, perforated and sharpened at the end, that attaches to a hose. It is pushed into the ground and gets the water directly to the roots. Surface watering is wasteful and inefficient. Rain rarely is adequate to do any good for trees.
For a larger tree, I sink the injector into the ground about 1 1/2 inches and let it run for an hour or so. Then I make four or five more similar insertions about 8 to 10 inches around the tree trunk. One injection, on the upper side if there is a slope, is usually enough for a shrub.
Researchers say that sending trees and shrubs into winter with adequate moisture is important. Evergreens, in particular, transpire through needles and small twigs all winter. Shrubs and deciduous trees transpire through small twigs.