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Flash floods and Urban flooding Finland

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Increased frequency of extreme rainfall increases the risk of sewage pipes being overloaded. There is an increased risk of back-flowing water and flooding of basements. Overloaded sewage pipes may lead to frequent and extensive overflowing of sewage, and therefore increased risks to health (1). Urban flooding could also be hazardous for underground cables, link boxes and basement transformers (2).

Moreover, intense precipitation and surface runoff may flush agricultural chemicals (e.g. pesticides) to rivers, resulting in massive fish kills (3).

Adaptation strategies

The consideration of floods caused by heavy rain is a great challenge in zoning and urban planning. From the point of view of municipal building regulations, it is important to know the flood risks. The means include surveying the routes of flood waters, proper design of stormwater drains, giving preference to permeable surfaces in construction, and the planning of basement rooms. More research on the impacts of rain-induced floods and changes in the intensity of rain will also be needed. Unbuilt flood areas, delay basins, impregnation areas and wetlands for the treatment of stormwater should be planned and utilised in the prevention of floods caused by heavy rains (4).

The fact that climate change may result in more frequent flooding and increase the risk of extreme flooding will lead to adjustments in the design of existing drainage arrangements on traffic routes and potential changes to the instructions concerning bridge openings and culverts, edge heights and other such issues (4).

A number of options for adaptations with respect to (urban) flash floods has been reported  (4):

  • Water drained from vehicle routes could be conducted into filtration basins so that emissions produced by traffic do not end up in water systems or groundwater.
  • Information on flood sensitive areas should be used as background information for the design of structures in risk areas.
  • The road traffic network has to be protected in different ways to endure extreme weather conditions.
  • In road construction, sufficient bridge openings, ditches and culvert structures must be taken into consideration with regard to heavy rains and floods. The design must be based on new research information on the impacts of climate change.
  • Material potentially carried by floods must be taken into consideration when renewing bridge structures.
  • The possibility of increased flooding must be taken into consideration in the design of underpasses in road structures, and, for example, new pumping stations must be added to underpasses to prevent overflows.
  • Railway beds have to be protected from floods and erosion.
  • Due to increased waves, mostly attributable to the shortening of the ice-covered period, harbour structures may need to be reinforced by using breakwaters, for example.
  • Securing the functionality of telecommunications in changing conditions must be taken into consideration in the design of structures. The replacement of overhead lines with underground cables will be considered increasingly.

At present, overflows of untreated wastewater following heavy rainfalls are a major source of pollution to the coastal receiving waters and there is a worry that increased rainfall could exacerbate the problem. Research on the potential impacts of climate change and continued urbanisation on waste and stormwater flows in the combined sewer of central Helsingborg, South Sweden, has shown that city growth and projected increases in precipitation, both together and alone, are set to worsen the current drainage problems. Conversely, system renovation and installation of sustainable urban drainage systems (SUDS) has a positive effect on the urban environment in general and can largely allay the adverse impacts of both urbanisation and climate change (5).


The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Finland.

  1. Ministry of the Environment of Finland (2006)
  2. Kirkinen et al. (2005)
  3. Kundzewicz (2009)
  4. Marttila et al.(2005)
  5. Semadeni-Davies et al. (2008a-b)