Here is some information on drought effect from Kim D. Coder at the Warnell School of Forest Resources, University of Georgia. It may not be relevant to your situation but very interesting.
From Mark Guthmiller, DNR Forest Health Specialist-Southern Region
Oaks:
I am anticipating an increase in dieback and mortality to all species of oaks due to increase in two-lined chestnut borer (TLCB) and Armillaria root rot. This will be one of the biggest impacts in southern Wisconsin. The last big outbreak of TLCB occurred during and after the drought of 1988 and 1989. How wide spread and severe this current problem will be is still hard to predict but if we continue in moderate to severe drought conditions we should anticipate a dramatic increase in this problem. One should also anticipate this problem to be worse in areas that have had other stress issues in the last two to three years such as moderate to severe defoliation, severe frost damage, or prolonged or repeated flooding. One should also anticipate this problem to continue one to three years after the drought breaks. Management can be a bit tricky. In some cases salvage harvesting may be a reasonable option and in some situations delaying harvest such as thinning in non-impacted areas may be the best option. Minnesota has a nice write up that addresses this issue. http://www.dnr.state.mn.us/treecare/forest_health/tlcb/management.html
A few other issues that may affect the condition of some oaks that may not be as bad as it appears:
Bur and white oaks:
-Cameraria leafminers: These have been common on bur oaks and can cause the leaf to brown up and look dramatic or as if the tree is dying. I have observed this in parts of southern WI recently . Yes, it can be an added stress but don’t assume the tree is dead as it will likely re-leaf just fine: http://www.fs.fed.us/r8/foresthealth/pubs/oakpests/p12.html
-Bur oak blight (Tubakia): This has been detected in many parts of southern WI and also is an added stress to the tree. How much of an impact this disease has to the health of a tree is still debatable. This disease shows up in mid to late summer and Iowa State staff have been observing this disease for the last couple of weeks (note the leaf underside dark lesions on the veins) : http://na.fs.fed.us/pubs/palerts/bur_oak_blight/bob_print.pdf
Other drought resources:
-WI DNR Drought Page: http://dnr.wi.gov/emergency/drought/
-NOAA Drought Page: http://www.drought.noaa.gov/
-NOAA Drought Map: http://www.cpc.ncep.noaa.gov/products/Drought/
Thanks Eric.