Since the beginning of the Neolithic, when sedentarization and, therefore, occupation of flat coastal areas or river valleys began, man has faced the challenge of dealing with floods. In Egypt and Mesopotamia, important river defenses have already been built, such as dams, canals to divert water, and improvements to channels in urban environments. Hydraulic works were also developed in Greece and Rome, both to obtain water for consumption and to avoid the risks entailed by settlements in vulnerable environments. In China, the construction of large banks in the rivers was already being done in the century in an attempt to deal with the monsoon floods. Also in Spain and northern Italy, the construction of mottes and reservoirs to regulate rivers has been notable since the Middle Ages.

Flood defenses are currently very advanced in developed countries. Prevention systems are based on dams, mounds, metal barriers, regulating reservoirs and improving the drainage capacity of river channels. Alert systems for dangerous situations are also highly developed through weather forecasting, observation of river gauges that determine a hydrological alert, and tsunami detection systems.

Defense against marine flooding caused by tides is highly developed in the Netherlands where a network of dikes regulate both internal and external waters. Venice and London also have similar defenses. Regulating reservoirs are very numerous in regions with a Mediterranean climate such as California and southern Europe and serve to store water in times of drought and contain river floods.

Other actions have been aimed at removing danger from cities by diverting the river channel, providing it in turn with greater drainage capacity, as in Valencia "Valencia (city)") or Seville. The canalization of rivers, such as the Rhine or the Segura "Segura (river)"), are larger works that have involved a comprehensive plan for the entire basin (increase in drainage capacity, specific diversions, reduction of meanders, construction and expansion of reservoirs, etc.). Some of these actions have been controversial due to their adverse effects, such as the elimination of meanders in the Rhine, which has favored the greater speed of the flood wave and therefore its greater virulence.

Legislation has made great progress by prohibiting construction in areas likely to be flooded with a return period of up to 100 years. The extensive cartography has made it possible to know which risk areas are for subsequent action on the ground. The reforestation of large areas in the upper and middle river basins also contributes to minimizing the effect of heavy rains and therefore the subsequent flooding. However, there remain risk areas, basically urbanized before the protective laws, some of them of high historical-artistic value such as Florence, which already suffered a major flood in 1966.

In developing countries, the prevention, warning and subsequent response systems are less developed, as has been seen in the successive typhoons that have devastated Bangladesh or in the tsunami that has devastated various coasts in Southeast Asia. Even so, international cooperation is favoring actions that lead to greater security for the population in these risk areas.

Primary effects

The primary effects of flooding include loss of life and damage to buildings and other structures, including bridges, sewage systems, roads, and canals.[7]​.

Floods also frequently damage power transmission networks and sometimes power generation plants, which then have knock-on effects caused by loss of power. This includes loss of drinking water treatment and supply, which may result in loss of drinking water or serious water contamination. It can also cause the loss of wastewater disposal facilities. The lack of drinking water combined with human sewage in flood waters increases the risk of waterborne diseases, which can include typhoid, giardia, cryptosporidium, cholera [8] and many other diseases, depending on the location of the flood.

"This happened in 2000, when hundreds of people in Mozambique fled to refugee camps after the Limpopo River flooded their homes. They soon fell ill and died from cholera, which is transmitted by unsanitary conditions, and malaria, transmitted by mosquitoes that thrived on the banks of swollen rivers."[9]​.

Damage to roads and transportation infrastructure can make it difficult to mobilize aid to those affected or provide emergency medical treatment.[10]​.

Flood waters often inundate agricultural land, making it unviable and preventing the planting or harvesting of crops, which can lead to food shortages for both humans and farm animals. A country's entire crops can be lost in extreme flooding circumstances. Some tree species may not survive prolonged flooding of their root systems.[11]​.

Side and long-term effects

Economic hardship due to a temporary decline in tourism, reconstruction costs, or food shortages causing price increases is a common side effect of severe flooding. The impact on those affected can cause psychological harm to those affected, particularly when deaths, serious injuries and loss of property occur.

Urban flooding can cause chronic wet homes, leading to indoor mold growth and resulting in adverse health effects, particularly respiratory symptoms.[12] Urban flooding also has significant economic implications for affected neighborhoods. In the United States, industry experts estimate that wet basements can reduce property values ​​by 10 to 25 percent and are cited among the top reasons for not purchasing a home.[13]​ According to the United States Federal Emergency Management Agency (FEMA), nearly 40 percent of small businesses never reopen after a flood.[14]​.

Floods can also have great destructive power. When water flows, it has the ability to knock down all types of buildings and objects, such as bridges, structures, houses, trees, cars. For example, in Bangladesh in 2007, a flood was responsible for the destruction of more than one million homes. And annually in the United States, floods cause more than $7 billion in damage.[15]​.

In prehistory, major floods occurred in some areas, as evidenced by geological remains. Thus, the formation of closed seas such as the Mediterranean or the Black Sea is due to tectonic movements and climatic changes that flooded these large areas. The end of the ice age had decisive consequences throughout the globe with the formation of new lakes and seas in areas that were not previously occupied by the sea.

As a result of the damage that floods have caused throughout history, many countries have developed strategies and methodologies to build flood risk maps. These maps show floods in relation to the potential impacts they may have on people, goods and economic activities. According to the guide established by IDEAM Archived March 28, 2020 at the Wayback Machine, there are several types of flood maps.

There are also free tools that allow you to build flood maps using radar images, such as Google Earth Engine, which allows you to carry out various online analyses. This platform was used to map the floods that occurred in August 2017 in Houston, Texas (United States) caused by Hurricane Harvey.

Se puede analizar estadísticamente una serie de caudales máximos anuales en un tramo de arroyo para estimar las crecidas de 100 años y las crecidas de otros intervalos de recurrencia allí. Estimaciones similares de muchos sitios en una región hidrológicamente similar pueden relacionarse con características medibles de cada cuenca de drenaje para permitir la estimación indirecta de los intervalos de recurrencia de inundaciones para tramos de arroyos sin datos suficientes para el análisis directo.

Los modelos de procesos físicos de tramos de canales generalmente se comprenden bien y calcularán la profundidad y el área de inundación para las condiciones del canal dadas y una tasa de flujo específica, como para su uso en el mapeo de llanuras aluviales y seguros contra inundaciones. Por el contrario, dada la zona de inundación observada de una inundación reciente y las condiciones del canal, un modelo puede calcular la tasa de flujo. Aplicado a varias configuraciones de canales potenciales y caudales, un modelo de alcance puede contribuir a seleccionar un diseño óptimo para un canal modificado. Varios modelos de alcance están disponibles a partir de 2015, ya sea modelos 1D (niveles de inundación medidos en el canal) o modelos 2D (profundidades de inundación variables medidas a lo largo de la extensión de una llanura de inundación). HEC-RAS,[17]​ el modelo del Centro de Ingeniería Hidráulica, es uno de los software más populares, aunque sólo sea porque está disponible de forma gratuita. Otros modelos, como TUFLOW,[18]​ combinan componentes 1D y 2D para derivar las profundidades de las inundaciones a lo largo de los canales de los ríos y de toda la llanura aluvial.

Los modelos de procesos físicos de cuencas de drenaje completas son aún más complejos. Aunque muchos procesos se comprenden bien en un punto o para un área pequeña, otros no se comprenden bien en todas las escalas y las interacciones de los procesos en condiciones climáticas normales o extremas pueden ser desconocidas. Los modelos de cuenca típicamente combinan componentes del proceso de la superficie terrestre (para estimar cuánta lluvia o deshielo llega a un canal) con una serie de modelos de alcance. Por ejemplo, un modelo de cuenca puede calcular el hidrograma de escorrentía que podría resultar de una tormenta de 100 años, aunque el intervalo de recurrencia de una tormenta rara vez es igual al de la inundación asociada. Los modelos de cuenca se utilizan comúnmente en la predicción y alerta de inundaciones, así como en el análisis de los efectos del cambio de uso de la tierra y el cambio climático.

Flood forecast

Anticipating floods before they occur allows you to take precautions and warn people[19]​ so they can be prepared in advance for flood conditions. For example, farmers can remove animals from low-lying areas and utilities can implement emergency provisions to redirect services if necessary. Emergency services can also take steps to have sufficient resources available in advance to respond to emergencies as they occur. People can evacuate areas that will be flooded.

To make flood forecasts more accurate for waterways, it is best to have a long historical data series that relates stream flows to past measured rainfall events.[20]​ Combining this historical information with real-time knowledge about volumetric capacity in catchment areas, such as reserve capacity in reservoirs, groundwater levels, and the degree of saturation of area aquifers, is also necessary to make flooding more accurate. precise. forecasts.

Radar estimates of rainfall and general weather forecasting techniques are also important components of a good flood forecast. In areas where good quality data is available, the intensity and height of a flood can be predicted with fairly good accuracy and a long lead time. The output of a flood forecast is typically an expected maximum water level and the probable time of its arrival at key locations along a waterway,[21] and may also allow calculation of the probable statistical return period of a flood. In many developed countries, urban areas at risk of flooding are protected against a 100-year flood, that is, a flood that has about a 63% chance of occurring in any 100-year time period.

According to the US National Weather Service (NWS) Northeast River Forecast Center (RFC) in Taunton, Massachusetts, a general rule of thumb for flood forecasting in urban areas is that at least 25 mm of rain is needed in about an hour. time to initiate significant water ponding on impervious surfaces. Many NWS RFCs routinely issue Flash Flood Guidance and Headwater Guidance, which indicate the general amount of rain that would need to fall in a short period of time to cause flash flooding or flooding in larger watersheds.[22]​.

In the United States, an integrated approach to real-time computer hydrological modeling uses observed data from the United States Geological Survey (USGS),[23]​ several cooperative observing networks,[24]​ several automated weather sensors, the NOAA National Operational Hydrological Remote Sensing Center (NOHRSC),[25]​ several hydropower companies, etc., combined with quantitative precipitation forecasts (QPF) of expected rainfall and/or snowmelt to generate forecasts. hydrological forecasts affecting both the United States and Canada, such as the St. Lawrence Seaway area.

The Global Flood Monitoring System, "GFMS", a computer tool that maps flood conditions around the world, is available online. Users anywhere in the world can use GFMS to determine when flooding may occur in their area. GFMS uses precipitation data from NASA's Earth observation satellites and the Global Precipitation Measurement Satellite, 'GPM'. GPM precipitation data is combined with a land surface model that incorporates vegetation cover, soil type, and terrain to determine how much water is being absorbed by the soil and how much water is flowing into the stream flow.

Users can view rainfall, flow, water depth and flood statistics every 3 hours, at every 12 kilometer grid point on a global map. The forecasts for these parameters are 5 days in the future. Users can zoom to view flood maps (areas estimated to be covered with water) at 1 kilometer resolution.[26]​[27]​.

Since the beginning of the Neolithic, when sedentarization and, therefore, occupation of flat coastal areas or river valleys began, man has faced the challenge of dealing with floods. In Egypt and Mesopotamia, important river defenses have already been built, such as dams, canals to divert water, and improvements to channels in urban environments. Hydraulic works were also developed in Greece and Rome, both to obtain water for consumption and to avoid the risks entailed by settlements in vulnerable environments. In China, the construction of large banks in the rivers was already being done in the century in an attempt to deal with the monsoon floods. Also in Spain and northern Italy, the construction of mottes and reservoirs to regulate rivers has been notable since the Middle Ages.

Flood defenses are currently very advanced in developed countries. Prevention systems are based on dams, mounds, metal barriers, regulating reservoirs and improving the drainage capacity of river channels. Alert systems for dangerous situations are also highly developed through weather forecasting, observation of river gauges that determine a hydrological alert, and tsunami detection systems.

Defense against marine flooding caused by tides is highly developed in the Netherlands where a network of dikes regulate both internal and external waters. Venice and London also have similar defenses. Regulating reservoirs are very numerous in regions with a Mediterranean climate such as California and southern Europe and serve to store water in times of drought and contain river floods.

Other actions have been aimed at removing danger from cities by diverting the river channel, providing it in turn with greater drainage capacity, as in Valencia "Valencia (city)") or Seville. The canalization of rivers, such as the Rhine or the Segura "Segura (river)"), are larger works that have involved a comprehensive plan for the entire basin (increase in drainage capacity, specific diversions, reduction of meanders, construction and expansion of reservoirs, etc.). Some of these actions have been controversial due to their adverse effects, such as the elimination of meanders in the Rhine, which has favored the greater speed of the flood wave and therefore its greater virulence.

Legislation has made great progress by prohibiting construction in areas likely to be flooded with a return period of up to 100 years. The extensive cartography has made it possible to know which risk areas are for subsequent action on the ground. The reforestation of large areas in the upper and middle river basins also contributes to minimizing the effect of heavy rains and therefore the subsequent flooding. However, there remain risk areas, basically urbanized before the protective laws, some of them of high historical-artistic value such as Florence, which already suffered a major flood in 1966.

In developing countries, the prevention, warning and subsequent response systems are less developed, as has been seen in the successive typhoons that have devastated Bangladesh or in the tsunami that has devastated various coasts in Southeast Asia. Even so, international cooperation is favoring actions that lead to greater security for the population in these risk areas.

Primary effects

The primary effects of flooding include loss of life and damage to buildings and other structures, including bridges, sewage systems, roads, and canals.[7]​.

Floods also frequently damage power transmission networks and sometimes power generation plants, which then have knock-on effects caused by loss of power. This includes loss of drinking water treatment and supply, which may result in loss of drinking water or serious water contamination. It can also cause the loss of wastewater disposal facilities. The lack of drinking water combined with human sewage in flood waters increases the risk of waterborne diseases, which can include typhoid, giardia, cryptosporidium, cholera [8] and many other diseases, depending on the location of the flood.

"This happened in 2000, when hundreds of people in Mozambique fled to refugee camps after the Limpopo River flooded their homes. They soon fell ill and died from cholera, which is transmitted by unsanitary conditions, and malaria, transmitted by mosquitoes that thrived on the banks of swollen rivers."[9]​.

Damage to roads and transportation infrastructure can make it difficult to mobilize aid to those affected or provide emergency medical treatment.[10]​.

Flood waters often inundate agricultural land, making it unviable and preventing the planting or harvesting of crops, which can lead to food shortages for both humans and farm animals. A country's entire crops can be lost in extreme flooding circumstances. Some tree species may not survive prolonged flooding of their root systems.[11]​.

Side and long-term effects

Economic hardship due to a temporary decline in tourism, reconstruction costs, or food shortages causing price increases is a common side effect of severe flooding. The impact on those affected can cause psychological harm to those affected, particularly when deaths, serious injuries and loss of property occur.

Urban flooding can cause chronic wet homes, leading to indoor mold growth and resulting in adverse health effects, particularly respiratory symptoms.[12] Urban flooding also has significant economic implications for affected neighborhoods. In the United States, industry experts estimate that wet basements can reduce property values ​​by 10 to 25 percent and are cited among the top reasons for not purchasing a home.[13]​ According to the United States Federal Emergency Management Agency (FEMA), nearly 40 percent of small businesses never reopen after a flood.[14]​.

Floods can also have great destructive power. When water flows, it has the ability to knock down all types of buildings and objects, such as bridges, structures, houses, trees, cars. For example, in Bangladesh in 2007, a flood was responsible for the destruction of more than one million homes. And annually in the United States, floods cause more than $7 billion in damage.[15]​.

In prehistory, major floods occurred in some areas, as evidenced by geological remains. Thus, the formation of closed seas such as the Mediterranean or the Black Sea is due to tectonic movements and climatic changes that flooded these large areas. The end of the ice age had decisive consequences throughout the globe with the formation of new lakes and seas in areas that were not previously occupied by the sea.

As a result of the damage that floods have caused throughout history, many countries have developed strategies and methodologies to build flood risk maps. These maps show floods in relation to the potential impacts they may have on people, goods and economic activities. According to the guide established by IDEAM Archived March 28, 2020 at the Wayback Machine, there are several types of flood maps.

There are also free tools that allow you to build flood maps using radar images, such as Google Earth Engine, which allows you to carry out various online analyses. This platform was used to map the floods that occurred in August 2017 in Houston, Texas (United States) caused by Hurricane Harvey.

Se puede analizar estadísticamente una serie de caudales máximos anuales en un tramo de arroyo para estimar las crecidas de 100 años y las crecidas de otros intervalos de recurrencia allí. Estimaciones similares de muchos sitios en una región hidrológicamente similar pueden relacionarse con características medibles de cada cuenca de drenaje para permitir la estimación indirecta de los intervalos de recurrencia de inundaciones para tramos de arroyos sin datos suficientes para el análisis directo.

Los modelos de procesos físicos de tramos de canales generalmente se comprenden bien y calcularán la profundidad y el área de inundación para las condiciones del canal dadas y una tasa de flujo específica, como para su uso en el mapeo de llanuras aluviales y seguros contra inundaciones. Por el contrario, dada la zona de inundación observada de una inundación reciente y las condiciones del canal, un modelo puede calcular la tasa de flujo. Aplicado a varias configuraciones de canales potenciales y caudales, un modelo de alcance puede contribuir a seleccionar un diseño óptimo para un canal modificado. Varios modelos de alcance están disponibles a partir de 2015, ya sea modelos 1D (niveles de inundación medidos en el canal) o modelos 2D (profundidades de inundación variables medidas a lo largo de la extensión de una llanura de inundación). HEC-RAS,[17]​ el modelo del Centro de Ingeniería Hidráulica, es uno de los software más populares, aunque sólo sea porque está disponible de forma gratuita. Otros modelos, como TUFLOW,[18]​ combinan componentes 1D y 2D para derivar las profundidades de las inundaciones a lo largo de los canales de los ríos y de toda la llanura aluvial.

Los modelos de procesos físicos de cuencas de drenaje completas son aún más complejos. Aunque muchos procesos se comprenden bien en un punto o para un área pequeña, otros no se comprenden bien en todas las escalas y las interacciones de los procesos en condiciones climáticas normales o extremas pueden ser desconocidas. Los modelos de cuenca típicamente combinan componentes del proceso de la superficie terrestre (para estimar cuánta lluvia o deshielo llega a un canal) con una serie de modelos de alcance. Por ejemplo, un modelo de cuenca puede calcular el hidrograma de escorrentía que podría resultar de una tormenta de 100 años, aunque el intervalo de recurrencia de una tormenta rara vez es igual al de la inundación asociada. Los modelos de cuenca se utilizan comúnmente en la predicción y alerta de inundaciones, así como en el análisis de los efectos del cambio de uso de la tierra y el cambio climático.

Flood forecast

Anticipating floods before they occur allows you to take precautions and warn people[19]​ so they can be prepared in advance for flood conditions. For example, farmers can remove animals from low-lying areas and utilities can implement emergency provisions to redirect services if necessary. Emergency services can also take steps to have sufficient resources available in advance to respond to emergencies as they occur. People can evacuate areas that will be flooded.

To make flood forecasts more accurate for waterways, it is best to have a long historical data series that relates stream flows to past measured rainfall events.[20]​ Combining this historical information with real-time knowledge about volumetric capacity in catchment areas, such as reserve capacity in reservoirs, groundwater levels, and the degree of saturation of area aquifers, is also necessary to make flooding more accurate. precise. forecasts.

Radar estimates of rainfall and general weather forecasting techniques are also important components of a good flood forecast. In areas where good quality data is available, the intensity and height of a flood can be predicted with fairly good accuracy and a long lead time. The output of a flood forecast is typically an expected maximum water level and the probable time of its arrival at key locations along a waterway,[21] and may also allow calculation of the probable statistical return period of a flood. In many developed countries, urban areas at risk of flooding are protected against a 100-year flood, that is, a flood that has about a 63% chance of occurring in any 100-year time period.

According to the US National Weather Service (NWS) Northeast River Forecast Center (RFC) in Taunton, Massachusetts, a general rule of thumb for flood forecasting in urban areas is that at least 25 mm of rain is needed in about an hour. time to initiate significant water ponding on impervious surfaces. Many NWS RFCs routinely issue Flash Flood Guidance and Headwater Guidance, which indicate the general amount of rain that would need to fall in a short period of time to cause flash flooding or flooding in larger watersheds.[22]​.

In the United States, an integrated approach to real-time computer hydrological modeling uses observed data from the United States Geological Survey (USGS),[23]​ several cooperative observing networks,[24]​ several automated weather sensors, the NOAA National Operational Hydrological Remote Sensing Center (NOHRSC),[25]​ several hydropower companies, etc., combined with quantitative precipitation forecasts (QPF) of expected rainfall and/or snowmelt to generate forecasts. hydrological forecasts affecting both the United States and Canada, such as the St. Lawrence Seaway area.

The Global Flood Monitoring System, "GFMS", a computer tool that maps flood conditions around the world, is available online. Users anywhere in the world can use GFMS to determine when flooding may occur in their area. GFMS uses precipitation data from NASA's Earth observation satellites and the Global Precipitation Measurement Satellite, 'GPM'. GPM precipitation data is combined with a land surface model that incorporates vegetation cover, soil type, and terrain to determine how much water is being absorbed by the soil and how much water is flowing into the stream flow.

Users can view rainfall, flow, water depth and flood statistics every 3 hours, at every 12 kilometer grid point on a global map. The forecasts for these parameters are 5 days in the future. Users can zoom to view flood maps (areas estimated to be covered with water) at 1 kilometer resolution.[26]​[27]​.