Highway 37 is flooded again, with a three-mile stretch east of Highway 101 inundated by as much as 5 feet of water less than a week after the previous flood receded.

With no place to pump the flood water, it could be several days before this important regional link reopens. The prior closure lasted more than a week.

For anyone who commutes to Marin County from the Sonoma Valley, Napa or Vallejo, or anyone headed the opposite direction, it’s a time-consuming nuisance.

Worse, these unprecedented floods may be more than a side-effect of our drought-busting winter. They could be a glimpse of what climate change and rising sea levels have in store for the North Bay.

Sonoma County’s transportation agency warns that high tides eventually could wash over parts of Highway 37 twice a day, and UC researchers say the segment between the Petaluma River and Lakeville Highway is at risk of “permanent inundation” if sea level rises 12 inches — about 20 percent of what some recent models project by the end of the century.

This is where we would like to tell you about an expedited plan to protect the highway and the thousands of people who use it daily from routine flooding.

But there isn’t any such plan.

Highway 37 is one of the lowest-lying highways in California, and it could be one of the first roads threatened by climate change, but flood-proofing and other improvements are nowhere to be found on the state’s list of infrastructure projects. Moreover, because it passes through parts of four counties over its relatively short 21-mile path, Highway 37 isn’t viewed by any of those counties as its top transportation priority. To their credit, however, the counties recently formed a panel to study traffic and flooding concerns.

The only pending proposal for Highway 37 is a private venture’s offer to build a four-lane causeway between Sears Point and Vallejo, where there are now just two lanes. The expansion would be paid for by imposing tolls.

The extra lanes are needed. Highway 37 already is congested, and daily traffic is projected to increase from 45,000 vehicles to 58,000 by 2040. The United Bridge Partners project — if it overcomes public opposition to toll roads — also would address potential impacts of rising sea levels east of Sears Point. But it doesn’t include the segment west of Sears Point, which has flooded twice this month and was given a “high vulnerability” rating in a UC study of climate impacts on Highway 37.

Potential solutions include relocating the road to a causeway or a bridge between Highway 101 and Sears Point at a cost of as much as $1.4 billion, according to the UC study. Another option is raising embankments along the highway at a cost of $460 million.

Highway 37 is a vital link between Interstate 80 and the North Bay for commercial traffic and commuters. Extended closures due to winter flooding are a headache for residents. A permanent loss of parts of the highway to rising sea levels would be an economic disaster. Flood-proofing won’t be inexpensive, but whatever approach state and local officials settle upon, these upgrades cannot wait.