Floods occur when peak discharge exceeds channel capacity, and this may be brought about naturally by intense precipitation (Wilson and Rashid (2005) Canad. Geogr./Géog. canad. 49, 1), snow- and ice-melt (Kaczmarek (2003) Risk Analys. 23, 3), the rifting of barriers, such as ice dams; the failure of man-made structures (Cioffi and Gallerana (2003) Rivers Res. & Applications 19, 1); deforestation and urbanization, which reduces infiltration and interception (Boardman (2003) TIBG 28); and by land drainage and the straightening and embankment of rivers (Gilvear and Black (1999) Hydrol. Scis J. 44, 3). Macklin and Rumsby (2007, TIBG 32, 2) show that the incidence and size of extreme floods have markedly decreased over the last 50 years. Extreme upland flooding appears to be associated with negative North Atlantic Oscillation index values.

Flood prevention and flood control measures include afforestation, the construction of relief channels and reservoirs, water meadow areas in which to divert flood water, and a ban on building in flood-prone environments, such as flood plains. These measures may increase with per capita income, individual preparedness, and/or experience with flooding, but may decrease with distance from a river, acceptability of flood risk, and provision of environmental information (Zhai et al. (2006) J. Am. Water Resources Ass. 42, 4). In more economically developed countries, there is a move for flood costs to be borne by the private citizen (Salthouse (2002) Insurance Res. & Practices 17, 1; Penning-Rowsell and Wilson (2006) TIBG 31). See Ono (2002) Australian Geogr. Studs 40, 2 on problems and conflicts arising from flood control in Hokkaido. Chen and Hou (2004) J. Am. Water Resources Ass. 40, 1 develop a multi-criterion, fuzzy recognition model for flood control.