Lightning
Lightning is a weather phase in The Sims 2: Seasons during heavy storms. If a Sim is outside there is a possibility they will get hit. Lightning can also be attracted to a lightning conductor, like a hot tub or a hot spring. Sims soaking in one of these during a storm will be hit by lightning VERY frequently. It is also very likely that after getting hit while IN the hot tub, the Sim will also be struck by lightning as soon as they step OUT of the hot tub, resulting in near instant death.
Lighting can also hit trees, causing them to catch fire. If you call the fire department they will give you a fine as the fire is usually out by the time they arrive.