Why Does It Rain?

The United States National Weather Service defines rain as liquid precipitation that falls down from the clouds to Earth in drops that measure 5 millimeters or more in diameter. Without rain, droughts occur that damage crops and threaten water supplies. Too much rain means potentially deadly and destructive floods and the loss of crops to funguses and other diseases that thrive in moisture.

Identification

Larger water droplets form in clouds when minute droplets collide with each other and stick together. The resulting droplets eventually become too heavy to remain in the cloud and falls to the ground; this is what is called rain. Cloud types such as nimbostratus and cumulonimbus are the most likely to be associated with rainfall. When the rain droplets are extremely tiny but still heavy enough to fall, they are classified as drizzle.

Misconceptions

Falling drops of rain are shown as being shaped like teardrops in cartoons and drawings, but they are not in reality. Smaller raindrops are almost perfectly round, while larger ones become more and more flattened, looking almost like the bottom portion of a hamburger bun due to the air pressure underneath them as they fall. Even larger raindrops look like parachutes that have opened up.

Time Frame

Rain is measurable with the help of a rain gauge, a device that collects rain and is calibrated to indicate how much has fallen. Weathermen classify rain as very light when less than a quarter of a millimeter falls in an hour's time and light rain as being between a quarter millimeter and 1 millimeter an hour. Between 1 and 4 millimeters an hour is moderate rain, with heavy rain described as the range between 4 and 16 millimeters in 60 minutes. Very heavy rain falls at the rate of 16 to 50 millimeters an hour, and the heaviest rain, extreme rain, comes out of the sky at more than 50 millimeters in the span of an hour.

Size

Since rainfalls records have begun to be kept accurately for the last century, the hardest it has rained was determined to be in Holt, Missouri when, during one storm, the rain came down and accumulated to a foot in a 42 minute span of time. An island in the Caribbean, Guadeloupe, once received an inch and a half of rain in one minute, while the highest average annual rainfall total on Earth belongs to Lloro, Colombia, which gets an average of 524 inches of rain a year.

Effects

Rain has a profound effect on the environment of a region. In areas where rain is very plentiful, you have lush vegetation and jungles known as rain forests. Where rain is scarce, you have dry deserts. Where rain is moderate, you have various ecosystems, each one in place in accordance to how much plant and animal life is supported by the average amount of rain that falls.