JIMANI, Dominican Republic?Aboard a UH1H helicopter that churns the torrid air above this western Dominican town, you can see exactly what went wrong and why hundreds of people are now dead.

The olive-green, 31-year-old transport chopper, flown by the Dominican Air Force, has spent the past week ploughing relentlessly back and forth above the course of a dried riverbed that suddenly surged with water eight days ago ? water that slammed through the town of Jimani, destroying hundreds of wood or concrete-block houses and ending some 400 lives, possibly considerably more.

Those aboard the trembling airframe keep their eyes glued to the bleached and washed-out terrain below.

They are looking for the remains of the dead.

“We found two bodies earlier today,” says First Lieutenant Mario Rivas.

Ten were found the day before, 14 the day before that.

From the air, it is not difficult to see just how it was that death came to this modest, low-rise trading town surrounded by mountains in western Dominican Republic on the border with Haiti.

The terrain on the Dominican side is parched country, with a sparse cover of organ-pipe cactus and acacia scrub, but it seems positively verdant in comparison to the land on the Haitian side of the border, which is bone-dry, almost desert, with no trees worthy of the name, just scattered bushes.

Among the most severely deforested countries on Earth, Haiti is a sort of ecological time bomb ? and last week, the bomb went off.

Rainstorms of rare and destructive force beat down upon mountains here, mountains that have known little in the way of water for decades now and where all the riverbeds have run dry.

Once, forests and the extensive root systems coiled beneath a layer of absorbent topsoil would have soaked up much of the rainfall. But these slopes are almost barren now, and nothing stood in the water’s path as it found its way into the old riverbeds and raced toward lower ground.

One of those beds used to carry a river known in Haiti as Rivière Soliette and in the Dominican Republic as Rio Blanco, but deforestation and a changing climate have turned all the rivers here to long ribbons of dun-coloured sand that swerve through the mountain ravines, mere memories of the water that used to be.

Even in the rainy season nowadays, they mostly remain dry.

The riverbed of the Rio Blanco cuts a deep path down through the mountains on the Haitian side of the border and swerves into the Dominican Republic, shaped like a natural canal with steep banks on both sides of its course ? until it reaches a plain above a lake called Enriquillo, where the banks suddenly recede and the riverbed sprawls from a width of about 20 metres to perhaps 200 metres.

It was here, where the former river’s course abruptly widens, that people began building houses a couple of decades ago, not thinking the river would ever return. Even the old bridge was destroyed long ago, the one that used to span the Rio Blanco, connecting the town of Jimani with the road that runs east toward Santo Domingo.

Just a few concrete pillars remain with nothing connecting them.

Of all the places they might have chosen to put their houses, the people who lived in these outlying barrios ? neighbourhoods that went by such names as Bate Bombita and La Cuarenta ? chose just about the worst place possible.

When rains of unprecedented force hit the region early last week, they caused torrents of water to race down the denuded mountain slopes, feeding into the old riverbeds, one of which bore straight for the largest town in the region, Jimani.

From a helicopter flying above the town, you can readily envision the scene last Monday at dawn, when the leading wave of the reinvigorated river surged between its banks and suddenly spread out across the floodplain where hundreds of houses had been built.

Those that the water did not sweep away at once were destroyed when the briefly revivified river burrowed beneath them, washing away the loose gravel on which they stood.

Now all that remains of a place where thousands of people once lived is a broad expanse of gravel and boulders, littered with scraps of wood and tin. Here and there, a few gaping rooms of what once were houses totter upon a precarious perch of gravel or sand.

A cemetery has been partly destroyed, and the tombs are littered with wood and other debris.

In the helicopter, First Lieutenant Rodolfo Cuevas waves his arm off to the east, where Lago Enriquillo glows turquoise in the afternoon sunshine. He shouts above the engine’s roar, explaining that some bodies were carried four or five kilometres downstream before snagging against an outcropping of some kind, a boulder or the branches of a tree.

But most of the corpses have been discovered now, and perhaps luckily this flight turns up no cadavers at all ? just the rotting remains of a lone horse.