When they bought their organic vegetable farm in South Royalton, Vt., slung along the fertile floodplain of the White River, Ashley Loehr and Antoine Guerlain took comfort in the dense buffer of shrubs and trees that lay between their fields and the gently swirling water.

It was 2021, a decade after the remnants of Hurricane Irene drove the river far over its banks, swamping the farm and wide swaths of the state. Determined to prevent another such disaster, the prior owner had proactively planted the trees, imagining a rising wall of woods that would at least make future flooding less grievous.

There was no way to know if the barrier, 35 feet wide, would be enough — until last July, when another devastating storm surged across Vermont. The river gathered force and busted through, again overtaking fields and destroying crops.

In the year since, Ms. Loehr and Mr. Guerlain, as well as some 3,000 other Vermont farmers hit hard by the two-day storm, have wrestled with a newly urgent reckoning: how to plan a future knowing that as the climate changes, so-called 100-year storms may strike every 10 years — or even more frequently.

Vermont farmers have long adapted to the twists and turns of climate: tapping maple trees earlier as winters have warmed, for example, and investing less in berry crops as hotter, wetter weather makes them more vulnerable to pests and fungus. But the shock of last summer’s catastrophic flooding — followed by another damaging deluge this month — underscored a level of risk that is hard to mitigate, given the state’s mountainous terrain and its proximity to the Atlantic.