A flood is an overflow of water that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrology and are of significant concern in agriculture, civil engineering and public health. Human changes to the environment often increase the intensity and frequency of flooding, for example land use changes such as deforestation and removal of wetlands, changes in waterway course or flood controls such as with levees, and larger environmental issues such as climate change and sea level rise. In particular climate change's increased rainfall and extreme weather events increases the severity of other causes for flooding, resulting in more intense floods and increased flood risk.
A rain gauge is an instrument used by meteorologists and hydrologists to gather and measure the amount of liquid precipitation over a predefined area, over a period of time. It is used to determine the depth of precipitation that occurs over a unit area and measure rainfall amount.
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and "precipitates" or falls. Thus, fog and mist are not precipitation but colloids, because the water vapor does not condense sufficiently to precipitate. Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called showers.
The 1968 Atlantic hurricane season was a below average hurricane season in which there were seven named storms. The season officially began on June 1 and lasted until November 30, dates which conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. Of the named storms, five strengthened into hurricanes; none however intensified into a major hurricane. Only four other seasons since the start of the satellite era—1972, 1986, 1994, and 2013—did not feature a major hurricane. The first system, Hurricane Abby, developed in the northwestern Caribbean on June 1. Abby moved northward and struck Cuba, bringing heavy rainfall and flooding to western portions of the island. Making landfall in Florida on June 4, Abby caused flooding and spawned four tornadoes, but left behind little damage. Overall, the hurricane resulted in six deaths and about $450,000 (1968 USD) in damage. In late June, Tropical Storm Candy brought minor flooding and spawned several tornadoes across portions of the Southern United States. Overall damage from the cyclone reached approximately $2.7 million.
The 1945 Atlantic hurricane season produced multiple landfalling tropical cyclones. It officially began on June 16 and lasted until October 31, dates delimiting the period when a majority of storms were perceived to form in the Atlantic Ocean. A total of 11 systems were documented, including a late-season cyclone retroactively added a decade later. Five of the eleven systems intensified into hurricanes, and two further attained their peaks as major hurricanes. Activity began with the formation of a tropical storm in the Caribbean on June 20, which then made landfalls in Florida and North Carolina at hurricane intensity, causing one death and at least $75,000 in damage. In late August, a Category 3 hurricane on the modern-day Saffir–Simpson hurricane wind scale struck the Texas coastline, with 3 deaths and $20.1 million in damage. The most powerful hurricane of the season, reaching Category 4 intensity, wrought severe damage throughout the Bahamas and East Coast of the United States, namely Florida, in mid-September; 26 people were killed and damage reached $60 million. A hurricane moved ashore the coastline of Belize in early October, causing one death, while the final cyclone of the year resulted in 5 deaths and $2 million in damage across Cuba and the Bahamas two weeks later. Overall, 36 people were killed and damage reached at least $82.85 million.
The 1940 Atlantic hurricane season was a generally average period of tropical cyclogenesis in 1940. Though the season had no official bounds, most tropical cyclone activity occurred during August and September. Throughout the year, fourteen tropical cyclones formed, of which nine reached tropical storm intensity; six were hurricanes. None of the hurricanes reached major hurricane intensity. Tropical cyclones that did not approach populated areas or shipping lanes, especially if they were relatively weak and of short duration, may have remained undetected. Because technologies such as satellite monitoring were not available until the 1960s, historical data on tropical cyclones from this period are often not reliable. As a result of a reanalysis project which analyzed the season in 2012, an additional hurricane was added to HURDAT. The year's first tropical storm formed on May 19 off the northern coast of Hispaniola. At the time, this was a rare occurrence, as only four other tropical disturbances were known to have formed prior during this period; since then, reanalysis of previous seasons has concluded that there were more than four tropical cyclones in May before 1940. The season's final system was a tropical disturbance situated in the Greater Antilles, which dissipated on November 8.
Hurricane Linda was a very powerful Category 5 hurricane that was also the second-most intense eastern Pacific hurricane on record, but surpassed 18 years later by Patricia. Forming from a tropical wave on September 9, 1997, Linda steadily intensified and reached hurricane status within 36 hours of developing. The storm rapidly intensified, reaching sustained winds of 185 mph (298 km/h) and an estimated central pressure of 902 millibars (26.6 inHg); both were records for the eastern Pacific until Hurricane Patricia surpassed them in 2015. The hurricane was briefly forecast to move toward southern California, but instead, it turned out to sea and lost its status as a tropical cyclone on September 17, before dissipating on September 21. Linda was the fifteenth tropical cyclone, thirteenth named storm, seventh hurricane, and fifth major hurricane of the 1997 Pacific hurricane season. Linda was also the most intense tropical cyclone worldwide in 1997.
The 1967 Pacific typhoon season has no official bounds; it ran year-round in 1967, but most tropical cyclones tend to form in the northwestern Pacific Ocean between June and December. These dates conventionally delimit the period of each year when most tropical cyclones form in the northwestern Pacific Ocean.
A tropical cyclone rainfall climatology is developed to determine rainfall characteristics of past tropical cyclones. A tropical cyclone rainfall climatology can be used to help forecast current or upcoming tropical cyclone impacts. The degree of a tropical cyclone rainfall impact depends upon speed of movement, storm size, and degree of vertical wind shear. One of the most significant threats from tropical cyclones is heavy rainfall. Large, slow moving, and non-sheared tropical cyclones produce the heaviest rains. The intensity of a tropical cyclone appears to have little bearing on its potential for rainfall over land, but satellite measurements over the last several years show that more intense tropical cyclones produce noticeably more rainfall over water. Flooding from tropical cyclones remains a significant cause of fatalities, particularly in low-lying areas.
Runoff is the flow of water across the earth, and is a major component in the hydrological cycle. Runoff that flows over land before reaching a watercourse is referred to as surface runoff or overland flow. Once in a watercourse, runoff is referred to as streamflow, channel runoff, or river runoff. Urban runoff is surface runoff created by urbanization.
Streamflow, or channel runoff, is the flow of water in streams and other channels, and is a major element of the water cycle. It is one runoff component, the movement of water from the land to waterbodies, the other component being surface runoff. Water flowing in channels comes from surface runoff from adjacent hillslopes, from groundwater flow out of the ground, and from water discharged from pipes. The discharge of water flowing in a channel is measured using stream gauges or can be estimated by the Manning equation. The record of flow over time is called a hydrograph. Flooding occurs when the volume of water exceeds the capacity of the channel.
The Tropical Rainfall Measuring Mission (TRMM) was a joint space mission between NASA and JAXA designed to monitor and study tropical rainfall. The term refers to both the mission itself and the satellite that the mission used to collect data. TRMM was part of NASA's Mission to Planet Earth, a long-term, coordinated research effort to study the Earth as a global system. The satellite was launched on 27 November 1997 from the Tanegashima Space Center in Tanegashima, Japan. TRMM operated for 17 years, including several mission extensions, before being decommissioned on 15 April 2015. TRMM re-entered Earth's atmosphere on 16 June 2015.
Tropical Storm Alberto was the first tropical storm of the 2006 Atlantic hurricane season. Forming on June 10 in the northwestern Caribbean, the storm moved generally to the north, reaching a maximum intensity of 70 mph (110 km/h) before weakening and moving ashore in the Big Bend area of Florida on June 13. Alberto then moved through eastern Georgia, North Carolina, and Virginia as a tropical depression before becoming extratropical on June 14.
Tropical Storm Carrie was a strong tropical storm that affected the East Coast of the United States in early September 1972. The third tropical cyclone of the 1972 Atlantic hurricane season, Carrie formed on August 29 from a complex sequence of meteorological events starting with the emergence of a tropical wave into the Atlantic in the middle of August. Tracking generally northward throughout its life, Carrie reached an initial peak intensity as a moderate tropical storm before nearly weakening back into tropical depression status. The storm began to intensify in a baroclinic environment after turning toward the northwest, its winds of 70,000 miles per hour (110,000 km/h) as it was transitioning into an extratropical system eclipsed the cyclone's previous maximum strength. The extratropical remnants of Carrie skirted eastern New England before making the landfall in Maine on September 4 and dissipating over the Gulf of Saint Lawrence during the next two days.
Tropical Storm Marco was the only tropical cyclone to make landfall on the United States during the 1990 Atlantic hurricane season. The 13th named storm of the season, Marco formed from a cold-core low pressure area along the northern coast of Cuba on October 9, and tracked northwestward through the eastern Gulf of Mexico. With most of its circulation over the western portion of Florida, Tropical Storm Marco produced 65 mph (105 km/h) winds over land. However, it weakened to a tropical depression before moving ashore near Cedar Key. The cyclone combined with a cold front and the remnants of Hurricane Klaus to produce heavy rainfall in Georgia and the Carolinas. After interacting with the nearby Hurricane Lili, Marco continued northward until being absorbed by a cold front on October 13.
The characteristics of United States rainfall climatology differ significantly across the United States and those under United States sovereignty. Late summer and fall tropical cyclones bring precipitation which falls across the Gulf and Atlantic states. During the winter, and spring, Pacific storm systems bring Hawaii and the western United States most of their precipitation. Low pressure systems moving up the East coast bring cold season precipitation to the Mid-West and Northeast states, as well as Great Salt Lake and the Finger Lakes region. The snow to liquid ratio across the contiguous United States averages 13:1, meaning 13 inches (330 mm) of snow melts down to 1 inch (25 mm) of water.
Severe Tropical Cyclone Bola was one of the costliest cyclones in the history of New Zealand, causing severe damage as an extratropical cyclone when it passed near the country in March 1988. It formed on February 24 to the north of Fiji, and tracking generally southwestward it reached hurricane-force winds near Vanuatu on February 28. The next day it generated peak wind velocities of 195 km/h (120 mph), though it quickly weakened as it accelerated southward. On March 4, Bola transitioned into an extratropical storm, passing to the north of the North Island of New Zealand on March 8. It weakened further and was absorbed by a stationary trough near the South Island on March 12.
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water for hydroelectric power plants, crop irrigation, and suitable conditions for many types of ecosystems.
Severe Tropical Storm Linfa, known in the Philippines as Tropical Storm Chedeng, brought deadly flooding to areas of the Philippines and Japan in May and June 2003. The fourth named storm within the northwestern Pacific that year, Linfa developed as a tropical depression just off the western coast of Luzon on May 25. The disturbance quickly intensified to reach tropical storm intensity a few hours after cyclogenesis. However, intensification leveled off as Linfa executed a small clockwise loop before a subsequent landfall on Luzon on May 27. Due to land interaction the storm temporarily weakened and decoupled before reforming in the Philippine Sea. Afterwards Linfa began reintensifying and reached its peak intensity on May 29 with maximum sustained winds of 100 km/h (65 mph) and a barometric pressure of 980 mbar. Following its peak the tropical storm began to deteriorate and transitioned into an extratropical cyclone on May 30; these extratropical remnants continued to track northward through Japan before dissipating in the Sea of Okhotsk on June 4.
Tropical Storm Morakot, known in the Philippines as Tropical Storm Juaning, brought significant rainfall to Taiwan before alleviating drought conditions in mainland China in August 2003. The tenth named storm in the western Pacific that year, Morakot spawned from an area of disturbed weather in the Philippine Sea on July 31. Tracking northwest, favorable conditions allowed for the intensification of the system to tropical storm strength on August 2. Morakot reached peak intensity later that day with winds of 85 km/h (50 mph) and a minimum barometric pressure of 992 mbar. This intensity was held for several hours until less conducive atmospheric conditions slightly weakened the system; this was followed by Morakot making landfall on southern Taiwan on August 3. Subsequently, the storm weakened and moved into the Taiwan Strait before making its final landfall near Quanzhou, China the next day. The storm quickly weakened over the Chinese mainland, and dissipated entirely several hours after landfall.
