They suggest grouping your trees into 3 different categories: Definitely Dead, Likely to Live, or Questionable
Pine trees are easier to assess than shade trees because a normally thick, green crown is replaced by red or brown needles indicating stress or mortality. Shade trees, such as oaks and hickories, may be more difficult since they can drop their leaves early and go into dormancy as an act of self preservation.
For a thorough description of the categories to see where your trees are, go to the Texas Forest Service website.
Also available from the Texas Forest Service is a video explaining easy tips of how to water your trees during drought.