It begins in the lush orchards and terraced farms skirting this mountaintop village, little rivulets of rainwater channeled away from precious crops to the sole paved road that plunges in twists and turns for 20 miles to the Haitian capital.
Once the runoff reaches the road, it joins an ochre-colored torrent already cascading along the surface, picking up speed and gravel as the byway becomes an aqueduct.
By the time the deluge makes its way to the suburb of Petionville, halfway from the Massif de la Selle promontory to the sea, the raging waters uproot shrubs, wash the ground out beneath homes' foundations and bulldoze anything in their path, even cars and the flimsier shanties.
"People put out their trash when it rains so the water carries it off," said Jane Wynne, a farmer who, along with her late father, has been battling for 50 years to raise environmental consciousness in order to halt the rains' annual devastation.
Misguided irrigation and drainage practices in Haiti's highlands, unregulated construction on hillsides and excessive cutting of endangered forests for fuel wood have combined to expose the area around Port-au-Prince to erosion that threatens to wipe out whole neighborhoods, rich and poor alike.
Damage from the heavy rain that falls almost nightly from June through November has been accelerating in recent years because every tree cut means less resistance to the water's flow. Every new home or business built in the hills above the capital scrapes away more grass and ground cover, leaving nothing to slow the runoff. Officials at the Environment Ministry blame corrupt local officials for failing to enforce laws against harvesting timber or building homes on publicly owned land.
"The problem is that the peasants don't have the means or the will to practice soil conservation," horticulturist Dimitri Norris said. "A peasant can live for a week from the proceeds of cutting one tree. He sees that as an immediate reward, whereas tending a fruit tree doesn't bring in that much income and requires a long-term commitment."
In a country with 70% unemployment, cutting trees and selling the wood to make charcoal is one of the few ways an indigent Haitian can make a living.
Foreign-funded organizations such as the Haitian Environmental Foundation are making inroads by promoting tree-planting and developing alternatives for fueling stoves.
Scientists working with the organization have developed briquettes made from compressed recycled paper that burn more efficiently and cleanly than charcoal, said Wynne, who operates a model farm here and works with international conservation and relief efforts. Bakeries are among the largest consumers of wood in Haiti, Wynne said, so the foundation is subsidizing conversion of their ovens to run on propane.
The U.S. Agency for International Development estimates that 71% of Haitian fuel consumption is of wood and charcoal. Last year the agency replaced 47,000 wood stoves with oil-fired burners and planted 600,000 trees in the most denuded and endangered regions.
But the baby steps toward education and recovery are drastically outpaced by behavior that few expect to change. As long as grinding poverty afflicts all but a tiny segment of this country, the majority of Haitians will be compelled to give priority to the daily demands of buying food and putting a roof over their families.
Although the government has 1,000 forest rangers to guard against wood poachers, men and women carrying bundles of slender tree trunks and logs brazenly tread the roadsides with their purloined burdens.
Fewer than 100,000 acres of forest are left in a country that was three-quarters woods when European explorers arrived five centuries ago -- Haitians have cut down all but about 1.5% of the original tree cover. The remaining woodlands are concentrated south of here in the La Visite and Foret des Pins national parks, unapproachable by vehicle in the rainy season because the surrounding roads have been washed out.
The consequences, seen in the low-lying slums of Port-au-Prince, are stunning. Knee-high muck -- mud, sewage, blown-off tin roofs, the occasional car -- covers the roads through Carrefour and Cite Soleil each morning until jobless men and boys can be induced by drivers' gratuities to shovel it to the side. At a car dealership on a sea-level plain near the airport, a lake of muck last month rose as high as the door handles, forcing much of the inventory off the sales lot.
Lerisson Beauvoir, a tailor who recently moved to Petionville from Les Cayes, rents a one-room shack perched precariously above a ravine -- into which dozens of similar structures have tumbled in recent rainstorms. He has rigged up troughs and drainpipes to divert water from the home's foundation but fears that the effort is only postponing the inevitable.
"There's no such thing as building codes. People just build wherever they want," he complained, gesturing at a new pink villa a mere dozen feet uphill from his house.
Norris, the horticulturist, acknowledged that rampant corruption in municipal governments allows reckless construction to persist. "There's a lot of advantage for officials to let people squat on state land. It's a very profitable business."