The only effective check on grass and brush fires is rain.
Given That ...
The only way to curb grass and brush fires is rain. If rain is below normal for an extended period of time, then there are many more such fires.
How Can it be That ...
Grass and brush fires cause less financial damage overall during severe drought than during normal rainfall?
Evaluate / Goal
To sharpen the paradox a little bit, it seems like we're trying to reconcile this comparison:
Severe Drought vs. Normal Rain
many more fires fewer fires
less $ damage more $ damage from fires from fires
So we need a way to explain why fewer fires during rainy times could be causing more financial damage than more fires during drier times.