A flood or heavy rain can seriously upset your termite defenses.
If you rely on soil chemical chemicals around or under your home, these can be buried by silt and debris making a bridge for the termites. The chemicals can also be washed out, so when the water goes away, check and organise a termite inspection a few weeks later.
Water that gets into your house (but not out again) tends to soak into timbers. Termites love to eat timber that’s damp. Fungi (rot) also has a better time and wood that’s partly rotted by fungi is often tastier for termites.
Subterranean termites have trouble getting around when their tunnels are full of water. If you scale it up, it is a bit like you or me trying to walk through honey. So they stay home or move to wherever is high and dry(ish). When the water drains away some of their tunnels will need repair and may be abandoned. They’ll move quickly to patch up access to their best food resources. Scary thing is that all that moisture in the soil makes their tunneling so much easier as they no longer need to carry in water to work. So, once re-established, subterraneans will go exploring and your barriers will be tested. After a flood or after drought-breaking rains, you should schedule an inspection the next Spring or Fall (Autumn), certainly before six months are up.
Floods can also move big bits of wood around. Sometimes these bits arrive with termite colonies inside. Sometimes floods cause timbers to be buried or mostly buried. Timbers that are in the soil are much nicer for termites as they don’t dry out quickly and the soil buffers temperature changes. Floods change things.
If flood waters sit around for extended periods, weeks or months, then termites populations may be reduced for a time.