Dozens of surveyors, coordinators and support volunteers will fan out across O'ahu Sunday evening as part of a statewide homeless head count that's expected to be the most comprehensive and accurate such canvass to date.

Not only will workers take a census of homeless beach dwellers, but those living under bridges, inside caves and up in the hills as well.

Experts believe the final tally, once the results have been completed in about a month, will show a substantial increase in the state's homeless population.

A tally two years ago estimated there were about 6,000 homeless people in Hawai'i.

"We have stories every day of people losing their housing because of rents going up or the owner selling and people not being able to find another unit in an affordable range," said Sandra Miyoshi, homeless program branch administrator for the Hawaii Public Housing Authority.

"That has increased our homeless population dramatically. And now we're going to find out how much."

Previous census efforts have produced varying results, in part because of differing methodologies used and because the transient nature of unsheltered people greatly complicates the process (some homeless people, for example, don't cooperate with such surveys because they have outstanding warrants or fear their children will be taken from them).

This head count disparity has been especially pronounced along O'ahu's Wai'anae Coast, the homeless focal point of the state, where tent encampments stretch for 16 miles on beaches from Nanakuli to Makua.

Various counts there in recent months have put the homeless population at from fewer than 800 to as many as 3,500 or more.

Kaulana Park, team leader for the Leeward Coast Operation HEART (homeless efforts achieving results together), the state's initiative to solve the Wai'anae Coast homeless crisis, says what's clear is that the number of homeless persons in Hawai'i is increasing and the largest concentration of them is on the Wai'anae Coast.

He said the study results would provide a better gauge of the problem compared to the head count figures from 2005.

But "surveys can be misleading," said Park, who in six months has coordinated the building of the 220-person Onelau'ena transitional homeless shelter in Kalaeloa and the soon to open 300-person Civic Center emergency shelter in Wai'anae.

"We'll know our success visually as the beaches get emptied out and the homeless begin moving into the shelters. Providing solutions is more important to us right now than finding out the actual number."

Still, homeless advocates such as Michael Ullman contend such counts are vital and that their accuracy would improve were surveys conducted quarterly rather than every couple of years.

"Counting the homeless is extremely important," Ullman said. "Just as we view unemployment as an important indicator to monitor on a monthly basis, homelessness is just as serious a problem and demands more frequent counting."

Miyoshi said Sunday's Ho-nolulu County survey is part of an unfunded, federally mandated point-in-time homeless count taken in all 50 states during the last week in January. She said teams counted homeless on Kaua'i on Friday, and head counts on Maui and the Big Island will be conducted Wednesday.

The Department of Housing and Urban Development requires that the counts be conducted every two years, and strict HUD guidelines are used throughout the nation.

The count two years ago concluded that Hawai'i's cumulative sheltered and unsheltered homeless population totaled 5,935. Since then, Hawai'i, and especially the Wai'anae Coast, has undergone a homeless explosion in large part because of skyrocketing rental increases at the same time available rental unit numbers have plummeted.

The previous Hawai'i count suffered quality-control problems, according to Miyoshi, because there wasn't money available to hire consultants to coordinate the project in Hawai'i's rural countries. Instead, local outreach agencies were asked to orchestrate their own Neighbor Island counts, she said.

This time professional consulting firms will coordinate the counts across the entire state. Miyoshi also said organizers this time have relied heavily on assistance from local service providers who personally know and work with homeless people in their areas.

"I think this will probably be one of the best counts that we've done," said Laura E. Thielen, chairwoman of Partners in Care, a voluntary agency of homeless service providers, community members and government entities that organized today's count.

"And the reason for that is there has been so much involvement from the people who are actually with folks out on the street, as well as the people themselves who are experiencing homelessness."

Thielen said about 25 percent of those surveyed will be asked to answer fewer than a dozen simple questions, such as the person's nationality, or the number of homeless family members.

Incentives such as slippers, snacks or food bank items will be provided to those who participate, as a way of saying thanks.

"We're still not hitting every single area, because that would pretty much be impossible," said Thielen. "But we've done an extensive list based on responses from the services providers as well as those who are experiencing homelessness on the sites we need to focus on.

"They are the experts on their own lives and have a better idea of how to do this."

Reach Will Hoover at whoover@honoluluadvertiser.com.