Kishore Mondol, a farmer in the low-lying deltas of southern Bangladesh, points at the four-foot-high platform of gray clay he and his wife have just struggled to build.

The mound is intended to keep their next home above ever-rising floodwaters. But even it won’t last long, he fears.

“Within the next 10 years, monsoon high tides will be flowing over this level,” he predicts.

With tidal floods fast worsening as a result of more intense rainfall and sea level rise, "this is the third time within 20 years we are moving our home higher,” complained Mr. Mondol, whose village lies in Khulna district, at the head of southwestern Bangladesh’s Sundarbans tidal forests.

Sea level rise and worsening storm surges are making life increasingly precarious in southern Bangladesh’s low-lying deltas, flooding homes and filling fields with salty water that keeps rice from growing.

Many former farmers have switched to raising tiger shrimp – now Bangladesh’s second biggest export after garments – in shallow ponds. But even the shrimp are now dying in many areas, hit by viral infections, local people say.

Instead, as waters continue to rise, women in the region have hit on a new, tough, and flood-friendly harvest: mud crabs.

In a village where most land lies 10 feet or less above sea level, and is flanked by major rivers on either side, flooding is an ever worsening worry for residents of Joymoni.

When this year’s monsoon arrives, “we fear water may come as high as 3 feet, especially during the full moon, as our side of the village has no protective embankment since cyclones Sidr washed it away” in 2007, Tripti Mondol, Kishore’s wife, told the Thomson Reuters Foundation.

Already, “salt is seeping into the very heart of our soil,” she said.

Subrat Chandra Gayen, another resident of Joymoni, said nearly 80 percent of families have had to give up on rice farming, which once provided food and an income for most people in the area, including women who sowed, harvested, and threshed it.

The loss of income has driven some farmers – particularly men – to migrate and look for work in cities, while many families raising shrimp have fallen into debt after taking high-interest loans from shrimp traders that they are now unable to pay back, local people say.

The Bangladesh government predicts rising sea level could displace about 20 million people from Bangladesh’s coastal districts by 2050.

Crabs, however, may help solve a big share of the problems, the village’s women say.

Khadija Begum, now does a brisk business buying and releasing batches of baby mangrove mud crabs into a shallow pond she has rented for $48 a year from a local land owner now living in Dhaka, the capital.

The tiny crabs, their shells still soft, are caught in local creeks by fishermen. She feeds them small amounts of waste fish once a day, she said, and within two weeks they are six times their original weight and have developed hard brown shells.

Ms. Begum catches them, ties their legs with jute string or straw, and packs them carefully into large bamboo baskets, which she sends her husband to sell at the Buddhamari local market, about 1.2 miles away.

From there they are transported to Dhaka and flown live to major importers in China, Japan, Taiwan, Malaysia, and Hong Kong, she said.

Fish traders grade the catch, with crabs with claws broken worth less, but those with a clump of bright orange-yellow eggs on their bellies – a delicacy for which South East Asians are willing to pay more – worth up to $26 a kilogram (about 2.2 pounds).

Begum and her husband’s earnings from crab sales now add up to between $780 and $840 a year, she said. The money has helped them send their eldest son to college in Khulna – a source of huge pride.

Bangladesh’s fisheries department, working with nonprofit organizations, has been encouraging farmers with salt-tainted fields to take up crab farming since 2011, with poor women a particular target for help.

Unlike shrimp farming, crabs can be raised in small ponds and demand less up-front investment, said Muhammod Zulfikar Ali, mayor of Mongla Port municipality.

Returns are also quick and, at the moment, higher than for shrimp and with lower disease risk, he said.

Crab farming’s growing momentum is reflected in Bangladesh’s export figures. According to the government’s Export Promotion Bureau, crab exports have climbed from $7 million in 2011 to more than $23 million in 2016.

Twenty percent of the country's current harvest is coming from backyard pond farmers in the country’s coastal Satkhira, Bagerhat, and Cox's Bazar districts, according to government data.

To further boost the industry, the government fisheries department is now trying to establish crab hatcheries. Currently most young crabs are caught in the wild, and catches have been falling with growing demand.

Some experts, however, warn that crab farming may not be enough to sustain families in increasingly risk-prone southern Bangladesh.

“Although crabs farms can be a lifeline against climate impacts they will only aggravate this unsustainable high-salinity” situation, said Pavel Partha, a researcher with the Bangladesh Resource Centre for Indigenous Knowledge (BARCIK).

Coastal villages, for instance, are running out of water they can drink. Many now have to buy potable water for nine months a year, from October to June, they say. Buying about 5 liters a day per person costs Mondol’s family about $3 a month.

Harjeet Singh, the global lead on climate change for charity ActionAid, said local peoples’ ability to adapt to the changing conditions was limited.

“This place is going to vanish in the next 20 years, the way the sea is rising,” he said, while visiting Joymoni. “Unsafe migration or crab farming are people’s own efforts, what we call autonomous adaptation, but it can only provide limited relief.”

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Government loans, to help communities scale-up adaptation efforts that work, could help, he said. But “there is a limit to how much [people] can raise their houses”.

This story was reported by Thomson Reuters Foundation.