We had a spell of drought here in N. Texas that lasted a couple years. We had on-and-off burn bans (mostly on) but when I called the Ft Worth Fire Marshall and asked about launching model rockets, he replied without hesitation that modrocs were fine, go right ahead and launch.
Never hurts to ask.
Also, if you can reduce the fire hazard by elevating the launcher, or covering the ground with a big tarp, or by having water and/or chemical fire extinguishers onsite, you can go a long ways toward convincing a hesitant official. Maybe you could launch from a paved area (edge of a parking lot?) and slant the launchers to target recovery over a grassy area?
Since you probably won't be able to get it in writing, make note of the phone conversation date, time, name of the person who approved your launch, his official "title" and phone number. Hang on to that info.