This summer I've noticed, as have others, many Bradford, or ornamental, pears with leaves that look like fall coloration. Usually these trees are older, probably in the 7+ year old range. Often these trees are also a little thin in the crown. I've looked at a few of these where I had access. Several of them had obvious girdling roots, where exposed roots were wrapping around the trunk, and the trunk was growing over the/around the trunk. This would certainly help explain the symptoms. Girdling roots cut off the flow of essential nutrients to the root system, and in severe cases, cause decay and rot in the affected portion of the trunk.
This may not explain every burgundy ornamental pear. The severe drought of the past 2 years, along with excessive rainfall this spring and summer resulting in saturated soils, could have resulted in injured roots becoming infected with root rot disease. If you have pears like this, check at the base for any injuries (mower, trimmer, etc) or roots curling around the trunk. That could be the cause.
