Coastal flooding
Coastal flooding occurs when dry and low-lying land is submerged (flooded) by seawater.[1] The range of a coastal flooding is a result of the elevation of floodwater that penetrates the inland which is controlled by the topography of the coastal land exposed to flooding.[1][2] The seawater can flood the land via several different paths: direct flooding, overtopping of a barrier,[3] or breaching of a barrier. Coastal flooding is largely a natural event. Due to the effects of climate change (e.g. sea level rise and an increase in extreme weather events) and an increase in the population living in coastal areas, the damage caused by coastal flood events has intensified and more people are being affected.[4]
Coastal areas are sometimes flooded by unusually high tides, such as spring tides, especially when compounded by high winds and storm surges. This was the cause of the North Sea flood of 1953 which flooded large swathes of the Netherlands and the East coast of England.
When humans modify the coastal environment this can make coastal flooding worse.[1][5][6][7] Extraction of water from groundwater reservoirs in the coastal zone can instigate subsidence of the land, thus increasing the risk of flooding.[5] Engineered protection structures along the coast, such as sea walls, alter the natural processes of the beach. This can lead to erosion on adjacent stretches of the coast which also increases the risk of flooding.[1][7][8]
The seawater can flood the land via several different paths:
Impacts[edit]
Social and economic impacts[edit]
The coastal zone (the area both within 100 kilometres distance of the coast and 100 metres elevation of sea level) is home to a large and growing proportion of the global population.[5][7] Over 50 percent of the global population and 65 percent of cities with populations over five million people are in the coastal zone.[33] In addition to the significant number of people at risk of coastal flooding, these coastal urban centres are producing a considerable amount of the global Gross Domestic Product (GDP).[7]
People's lives, homes, businesses, and city infrastructure like roads, railways, and industrial plants are all at risk of coastal flooding with massive potential social and economic costs.[34][35][36] The recent earthquakes and tsunami in Indonesia in 2004 and in Japan in March 2011 clearly illustrate the devastation coastal flooding can produce. Indirect economic costs can be incurred if economically important sandy beaches are eroded resulting in a loss of tourism in areas dependent on the attractiveness of those beaches.[31]
Environmental impacts[edit]
Coastal flooding can result in a wide variety of environmental impacts on different spatial and temporal scales. Flooding can destroy coastal habitats such as coastal wetlands and estuaries and can erode dune systems.[10][5][31][33] These places are characterized by their high biological diversity therefore coastal flooding can cause significant biodiversity loss and potentially species extinctions.[23] In addition to this, these coastal features are the coasts natural buffering system against storm waves; consistent coastal flooding and sea-level rise can cause this natural protection to be reduced allowing waves to penetrate greater distances inland exacerbating erosion and furthering coastal flooding.[5] "By 2050, “moderate” (typically damaging) flooding is expected to occur, on average, more than 10 times as often as it does today, and can be intensified by local factors."[37]
Prolonged inundation of seawater after flooding can also cause salination of agriculturally productive soils thus resulting in a loss of productivity for long periods of time.[1][31] Food crops and forests can be completely killed off by salination of soils or wiped out by the movement of floodwaters.[5] Coastal freshwater bodies including lakes, lagoons, and coastal freshwater aquifers can also be affected by saltwater intrusion.[10][5][33] This can destroy these water bodies as habitats for freshwater organisms and sources of drinking water for towns and cities.[5][33]