Major Rainfall
Haiti's deadly 2004 and 2009 floods were each caused by a tropical storms and hurricanes. Sharing an island with the Dominican Republic, Haiti is surrounded by the warm waters (approximately 26.5 degrees Celsius) that can supply the thermal energy necessary for the formation of thunderstorm clusters. While the Haitian environment has adapted to heavy seasonal rainfall, 5-foot deluges easily overpowered the island's geography.
In 2004, an edge of Hurricane Ivan saturated southwestern Haiti, setting the stage for tropical storm Jeanne. Because Jeanne moved slowly over Haiti, it had time to dump several feet of rain onto the already waterlogged land.
In 2009, a back-to-back assault by tropical storms Gustav and Hanna submerged much of the region in nearly 7 feet of floodwater.
Geography
Haiti is an island, so one might wonder why the floodwater didn't simply flow back into the ocean. While Haiti's geography is fairly hilly around the coast and inland, many of the valleys are below sea level. Although Haiti's elevation generally increases the farther one moves inland, the island is not cone-shaped. Rather, the hilly, uneven landscape lends itself to flash flooding. For this reason, three major dams were built to help control water levels in the vulnerable lowlands.
Deforestation
Originally, the warm climate and heavy rainfall encouraged dense, tropical forests to grow on Haiti's fertile hillsides. This vegetation had large root systems, which bound the soil. In addition to draining excess water from the soil (to nourish the leaves above), these roots helped hold the grains of dirt, rock and silt in place.
Starting with European colonists who cut down forests to plant indigo and sugar cane, humans gradually destroyed the native hillside root systems. The dense, plantation-style root system was an imperfect replacement that eventually gave rise to small, crop-killing floods in the valleys.
By the 20th century, the government had begun to plant trees in place of crops to help fight floods and landslides. Unfortunately, poverty became so rampant toward the end of the century that villagers began cutting down the trees and turning them into charcoal, which they then sold for food. Without crops or trees on the hills, the soil lost most of its water-holding capacity, leading to flash floods and frequent mudslides.
Tags: root systems, tropical storms