The sea is gradually swallowing up shoreline along the Gulf of Thailand's southern coast, altering life for Songkhla province's residents.

Though each year more land gives way to ocean water, according to seaside community residents, few seem to know if climate change is behind the erosion.

One area constantly threatened by rising sea levels is the low-lying finger of land acting as a barrier between the gulf and Songkhla Lake, Thailand's largest natural lake. The spit of land is about 75km long and 3km wide, and comprises three districts of Songkhla.

Retired Bangkok finance lecturer Chana Phadungath says his birthplace in Ranot's Pak Trae sub-district now lies underwater 20m off shore.

"I am here from Bangkok to visit my grandfather, who is now in his 90s," he told Khabar Southeast Asia. "The sea has been reclaiming this land since he was born and the house he lives in is the third we have built. It is the same all along this coast."

The area is "nice this time of year", he said, but when monsoon winds shift to an onshore direction – especially from December to February – waves "pound the shoreline and erosion occurs".

Like many other coastal towns and municipalities , Pak Trae constructed a series of seawalls. But none have halted the erosion, as pounding waves breached or damaged all of them.

Department of Marine and Coastal Resources (DMCR) Planning Director Dhana Yingcharoen has researched the Songkhla coast.

"In my opinion, construction is the major factor causing erosion along the coastline, but global warming and rising sea levels might also be having a smaller impact," Dhana told Khabar.

Farther south, in the predominantly Muslim village of Bor Tru, the local mosque that once occupied the heart of the community, now sits some 20m from a large, intact seawall.

"I was born in this village," 74-year-old Kuiya Chaiyakit told Khabar as she sat at home knitting a nylon fishing net. "The sea took our old home years ago, so now we are forced to live behind this seawall, with no good view of the ocean."

She said she wonders why storms and waves are now more severe than in the past, but does not know. "It is much harder to catch fish than it used to be, that's for sure," Kuiya said.

Dhana said research was under way on ways to improve area land use and slow erosion, such as planting bamboo. Leaves of the fast-growing plant cover the soil, helping protect it from sediment loads and thereby slowing erosion.