They've made their homes in dry riverbeds and on steep hillsides. Using discarded tires, garage doors and movie billboards, hundreds of poor families have turned this city's canyons into colonias.
Authorities turned their heads as residents packed into the shantytowns, squatting on public land and stealing electricity and water from adjacent neighborhoods.
But with El Nino making a comeback this year and a history of floods, Tijuana city officials aren't taking any chances. They are evicting hundreds of families and relocating many to higher ground to avoid a repeat of the last El Nino, when harsh storms and flash floods in 1998 swept through Baja California with deadly strength.
While heavy rains make a mess of roads in San Diego, they sweep people to their deaths in flood zones south of the border. City officials have already urged many residents to leave the high-risk areas and plan to evict families soon.
The season's first rains struck the region last month, saturating hillsides and causing minor flooding on some Tijuana streets. The border city is bracing for much worse; forecasters warn of storms throughout the winter.
"It's time to do something," said Antonio Rosquillas, Tijuana's civil protection director. The squatters, he said, "are risking their belongings and their lives."
In recent winters, the government has warned residents, but has been unable to offer them new places to live. This season, authorities have set aside land and are giving residents a chance to buy plots.
City workers pledged to help them move, and volunteer organizations plan to assist with home construction.
The designated land, however, will accommodate only about one-fourth of the 1,200 households targeted for eviction, officials said. And the price, $4,000, is far beyond the reach of most residents in the shantytowns.
Officials say a buyer has to pay only a $400 down payment now, and even that can be spread over time, if necessary. But the cost is still prohibitive for many, putting the alternative housing out of reach. Those families will have to find their own places to live -- or to squat. Emergency shelters will be available during powerful storms, officials said.
The problems surrounding the shantytowns have worsened in the last decade as Mexicans from rural areas in the center of the country have migrated to the border in large numbers. They hoped to find work with the U.S. firms that built plants by the score south of the border as a result of the North American Free Trade Agreement. Officials estimate that the population of Baja California has more than doubled in that period.
Many new residents found work, but their weekly salaries often did not cover household expenses. So they found rent-free places to live, often on land deemed unsuitable for houses and vulnerable to erosion and flooding.
On the east side of Tijuana, in a neighborhood called "the Eagle's Nest," a waterfall of sewage runs down the hillside. Children play on rusty metal cables. Bags of trash block dirt walkways. Wobbly wood ladders lead up to the roads that sandwich the settlement.
During the day, Norma Valle runs a makeshift general store in the colonia, selling eggs, canned vegetables, cereal and potato chips. At night, Valle, her husband, their two teenage daughters and a 2-year-old grandson lay down blankets next to two old refrigerators and turn the store into a bedroom.
City officials periodically inspect the high-risk neighborhoods, posting red stickers on the homes that are most at risk of collapsing or being swept away in the floods. Two such stickers are pasted to Valle's home, reading "High Danger. Evacuation is recommended for your own safety."
Valle said she ignores the stickers. "We are used to living here," she said. "Where are we going to go?"
In early December, rumors of eviction started spreading. Many residents feared that bulldozers would come through and destroy their homes without warning. Mayor Jesus Gonzalez Reyes toured the area in December, calming residents' fears and telling them that city workers would help move their belongings and building materials.
According to Jorge Ramos Hernandez, the city's director of social development, about 80% of the families in high-risk zones said they were willing to relocate. About 40 families have been taken to see the new plots of land and are raising money for the down payments, city officials said.
But recent interviews with riverbed residents present a different picture. Many families said they don't want to leave, insisting that the rains don't scare them and that the new plots are too far from their jobs. Others say they can't afford to buy land.
"We're here because we have nowhere to go," said Adrian Grisostomo, who came to Tijuana from Michoacan in search of work.
Griselda Nunez and her husband, Alejandro Carbajan, made an outdoor kitchen by spreading a scrap of carpet over dirt and setting up a card table. A shower curtain serves as a door into two other rooms.
On a December morning, they sat eating beans and tortillas, while their 6-year-old son watched television on a small set inside. "You fall in love with your house, even if it's ugly," Carbajan said. "It's mine."
City officials say those who don't want to leave haven't been in Tijuana long enough to see the catastrophic damage the storms inflict, especially on shacks made of flimsy plywood.
In 1993, torrential storms battered Tijuana for nearly two weeks, flooding canyons and destroying squatters' settlements. More than 30 people died and about 10,000 were left homeless. Five years later, El Nino struck again and storm water flooded makeshift communities and killed nearly a dozen people, Rosquillas said.
City officials say they know that many squatters will return to the canyons and hillsides after the rains pass.
Rosquillas said the shantytowns will exist as long as Tijuana housing is tight and unaffordable for many. "It's not a long-term solution," he said of the current moves. "If you remove one family today, a new family comes in."