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Torrential downpours led to flash flooding across Haiti this week, claiming the lives of dozens of people and displacing thousands of families. A low-pressure system brought intense rainstorms across Haiti causing numerous rivers to overflow, flash flooding and many landslides in areas. The rain began two days after the start of hurricane season. 

What causes these intense torrential downpours in Haiti?

Several contributing factors lead to extreme rainfall (and drought) conditions. A combination of global temperatures in the atmosphere, earth, and ocean all influence the way heat and moisture move around the planet. Gases move from high pressure to low pressure because they are trying to equalize. The bigger the difference in pressure, the faster the air will move from high pressure to low pressure. Its movement we call wind.

Global winds, which occur as belts that circle the planet, circulate that heat and moisture through differing air pressures that are created by the temperature and moisture differences. When warmer temperatures cause more water to evaporate into the air and allow that air to hold more water, the stage is set for heavier downpours.

When the earth's surface is warmed unevenly by the sun because of it being tilted on its axis, the rays of the sun fall directly on the equator, heating the equator more intensely than other regions. Haiti sits just over 1300 miles north of the equator.

Both the ocean and atmosphere will move the heat -- the atmosphere will move the heat quickly and the ocean more slowly. But the ocean will absorb and store more of the heat.

So when oceanic temperatures rise, that heat, as a form of energy, will fuel the more intense storms, by moving the warm, moist air upward, and then into the torrential downpour that follows.

Some excellent videos:

     WATCH  |  Thunderstorms 101 (3:36min)

     WATCH  |  Hurricanes 101 (2:57min)

     WATCH  |  The Ocean (6:00min)

     WATCH  |  Nature is Speaking - Coral Reef (1:36min)

     WATCH  |  Nature is Speaking - Ocean (2:03min)

Some excellent reads:

     READ |  How Trees Prevent Flooding

     READ |  How Trees Keep Soil in Place