two months after intense rains began to pound much of South America, rivers along the northwest coast of Peru remained flooded. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured the top image of the flooded river systems on April 1, 2008. Streams and pools of dark blue water dominate what was a tan-pink desert in early February, immediately before the rains began.
The images show the Sechura Desert in northwestern Peru near the border with Ecuador. The large image shows additional flooding extending north into Ecuador. To increase the contrast between muddy water and land, which often look the same in photo-like images, the image was made with both visible and infrared light. This false-color combination colors water black and dark blue and bare or sparsely vegetated earth tan. Plant-covered land is green, and clouds are turquoise and white.
Floods throughout Peru damaged farmland, homes, and transportation networks, reported the United Nations Office for the Coordination of Humanitarian Affairs. On February 28, the government of Peru declared a state of emergency in Piura and Lambayeque, the regions included in this image, and in Tumbes, the region immediately north of the area shown, and in Ucayali, a region in central Peru along the Brazilian border. More than 450,000 people were affected by flooding throughout Peru as of March 12, said the United Nations.

Raindrops impact at their terminal velocity, which is greater for larger drops. At sea level and without wind, 0.5 mm drizzle impacts at about 2 m/s, while large 5 mm drops impact at around 9 m/s.^[4] The sound of raindrops hitting water is caused by bubbles of air oscillating underwater. See droplet's sound.

Generally, rain has a pH slightly under 6. This is because atmospheric carbon dioxide dissolves in the droplet to form minute quantities of carbonic acid, which then partially dissociates, lowering the pH. In some desert areas, airborne dust contains enough calcium carbonate to counter the natural acidity of precipitation, and rainfall can be neutral or even alkaline. Rain below pH 5.6 is considered acid rain.

Effect on agriculture

Precipitation, especially rain, has a dramatic effect on agriculture. All plants need at least some water to survive, therefore rain (being the most effective means of watering) is important to agriculture. While a regular rain pattern is usually vital to healthy plants, too much or too little rainfall can be harmful, even devastating to crops. Drought can kill crops in massive numbers, while overly wet weather can cause disease and harmful fungus. Plants need varying amounts of rainfall to survive. For example, cacti need small amounts of water while tropical plants may need up to hundreds of inches of rain per year to survive.

Agriculture of all nations at least to some extent is dependent on rain. Indian agriculture, for example, (which accounts for 25 percent of the GDP and employs 70 percent of the nation's population) is heavily dependent on the rains, especially crops like cotton, rice, oilseeds and coarse grains. A delay of a few days in the arrival of the monsoon can, and does, badly affect the economy, as evidenced in the numerous droughts in India in the 90s.

Culture

Cultural attitudes towards rain differ across the world. In the largely temperate Europe, rain metaphorically has a sad and negative connotation — reflected in children's rhymes like Rain Rain Go Away — in contrast to the bright and happy sun. Though the traditional notion of rain in the Western World is negative, rain can also bring joy, as some consider it to be soothing or enjoy the aesthetic appeal of it. In dry places, such as parts of Africa, Australia, India, the Western United States, and the Middle East, rain is greeted with euphoria. (In Botswana, the Setswana word for rain, "pula," is used as the name of the national currency, in recognition of the economic importance of rain in this desert country.)

Several cultures have developed means of dealing with rain and have developed numerous protection devices such as umbrellas and raincoats, and diversion devices such as gutters and storm drains that lead rains to sewers. Many people also prefer to stay inside on rainy days, especially in tropical climates where rain is usually accompanied by thunderstorms or is extremely heavy (as in a monsoon). Rain may be harvested, though rainwater is rarely pure (as acid rain occurs naturally), or used as greywater. Excessive rain, particularly after a dry period that has hardened the soil so that it cannot absorb water, can cause flood

Many people find the scent during and immediately after rain especially pleasant or distinctive. The source of this scent is petrichor, an oil produced by plants, then absorbed by rocks and soil, and later released into the air during rainfall. Light or heavy rain is sometimes seen as romantic.

References
United Nations Office for the Coordination of Humanitarian Affairs. (2008, March 12). Peru: Floods (as of 05 March 2008) location map. Published on ReliefWeb. Accessed April 3, 2008.