In the United States, an average of some 70 percent of the annual precipitation returns to the atmosphere by evaporation from land and water surfaces and by transpiration from vegetation. In a more natural or undeveloped area, the direct runoff would be considerably less. Impervious surfaces and urban buildup causes rainfall to runoff much quicker, and with greater flooding consequences, during heavy rains.įor example, the direct runoff in a highly urbanized area is relatively great, not only because of the density of roofs and impermeable pavements permits less rain to infiltrate the ground, but also because storm-sewer systems carry more water directly to the streams and lakes.
Wide spread flooding in Lithia Springs, Georgia just west of downtown Atlanta, after epic rainfall, 22 Sept. What happens to the water after it reaches the ground depends upon many factors such as the rate of rainfall, topography, soil condition, density of vegetation, temperature, and the extent of urbanization. This is equivalent to about 1,430 cubic miles of water each year. Waialeale even experienced more than 642 inches of rain from July 1947 to July 1948! If you think that's something, Cherrapunji holds the single year record of 905 inches measured in 1861!īy contrast, the conterminous (the 48 "lower" states) United States receives enough precipitation during an average year to cover the States to a depth of about 30 inches. Waialeale, Hawaii, where an average of 373 inches of rain has fallen annually between the years 19. In case you're wondering, the wettest place in the United States, as shown by data collected by the Western Regional Climate Center, is on Mt. The world's wettest spot, Mawsynram, in Northeastern India, experienced a mean of 494 inches of rain a year during the years 1989-2010, replacing the previous placeholder, Cherrapunji, also in Northeastern India, where a mean of 471 inches fell during the same period. One of the driest spots on Earth is Iquique, Chile, where no rain fell for 14 years. The amount of precipitation that falls around the world may range from less than 0.1 inch per year in some deserts to more than 900 inches per year in the tropics. Water vapor ( evaporated from oceans, lakes, forests, fields, animals, and plants) condenses and returns to Earth as precipitation, once again replenishing reservoirs, lakes, rivers, underground aquifers, and other sources of water and providing the moisture required by plants and animals. A localized heavy summer rainstorm in ColoradoHere is a classic summer rainstorm they are often small but intense. Other rain events are more "frontal" in nature, with large nimbostratus types of clouds bringing precipitation over a large area.įortunately for everyone, water is a renewable resource that moves in a cycle with neither beginning nor end (but, you can put in your vote as to where you think it begins).