The wildfire scenario that experts say could destroy the western half of Austin, upending countless lives and destroying tens of thousands of luxury homes, ironically begins with water—specifically, a tropical storm birthed by the Gulf of Mexico. Once inland, forecasters predict, the storm would sweep across southern Texas before coming to rest northwest of the state capital, where it could unleash 35-mile-per-hour gusts of wind upon the city for the better part of a day. If this occurs when conditions are right—that is, when humidity is low, summer temperatures are high, and months of drought have turned the area’s cedar trees into veritable matchsticks—the only thing standing between Austin and a historic disaster could be a single spark. It could come from almost anywhere: a…