Ask Mr. Smarty Plants

It is possible that your Ulmus crassifolia (Cedar elm) has bacterial leaf scorch.  TAMU AgriLIFE Extension Texas Plant Disease Handbook's entry for Elm (Ulmus spp.) lists common diseases and pests and elm bacterial leaf scorch is listed as one of them.  This article from the United States National Arboretum certainly describes symptoms similar to those of your trees, however, the article says:

"The challenge is that the symptoms can be easily mistaken for physiological leaf scorch or early fall color. However, since a number of other diseases, as well as cultural problems, can mimic bacterial leaf scorch symptoms, it has been recommended that suspected infections be confirmed by sending samples to a diagnostic clinic before concluding the tree is infected with the bacterium."

If your tree does have bacterial leaf scorch, I'm afraid there isn't any effective treatment for it—either for curing it or preventing it.  The best thing you can do is to prune and keep the tree looking as nice as possible for as long as possible until it dies.  You can check with your Denton County Texas AgriLIFE Extension Service office to see if bacterial leaf scorch has been reported in the area.  A professional arborist should be able to tell you if your tree is infected with bacterial leaf scorch.   You can go to TreesAreGood.com and plug in your zipcode to find a professional arborist for your area.

Even though bacterial leaf scorch is a possibility, given the severity and length of our current drought, your tree may just be experiencing drought stress even though it is described as a drought tolerant tree. You said that you had done some watering.  Are you still watering?   If you aren't watering, you should be.  You can find an article from the City of Austin Urban Forestry Division, Supplemental Watering of Trees During Periods of Drought, with detailed recommendations on how much and how to water as well as other measures that will help drought-stressed trees.  I do know that cedar elms are one of the first deciduous trees to turn yellow and lose their leaves in the fall.  Your tree may just be reacting to the stress by doing this earlier than usual and may leafout normally in the spring.  Watering will help it recover if that is the case.