User:Iveerik/2023 Norway floods

In August 2023, large flooding occurred in Eastern Norway following Storm Hans.

Metheorologically, Southern Norway is divided between a western

Topographically, Southern Norway is split along a near-continuous mountainous area from Setesdal in the south, through Jotunheimen over Hardangervidda, Dovrefjell and Rondane into Kjølen at the border with Sweden (part of the Scandinavian Mountains). The mountains also cause orographic precipitation, with the western (windward) side prone to heavy rainfalls stemming from low-pressure areas moving in from the North Sea. The eastern (leeward) side tends to have much less precipitation. For instance, the city of Bergen on the west coast has an annual mean precipitation of 2250 mm, while Elverum near the border to Sweden respectively has 670 mm.

On both sides of the mountains the terrain slopes downwards, but on the eastern side the slopes are longer. Further south, the terrain becomes more or less flat, for example near the base of Østerdalen or Hadeland north of Oslo. As these areas near the end of the drainage basin, they are at risk from flooding at much lower levels of rain than on the western side.

In 1995, the previous major flooding in Eastern Norway occurred. The flooding was caused by an unusually long winter, then followed by heavy rainfalls in early June. This resulted in the Gudbrandsdalslågen and Glomma rivers reaching 100-year-highs, causing widespread damage in the lower parts of Gudbrandsdalen and Østerdalen. The damage caused by the 1995 flooding was estimated to 1,8 billion NOK (over 3 billion NOK adjusted for inflation, eq. €300 million).

In early August, two windstorms coming from different directions coalesced in the Baltic Sea south of the Swedish coast. One of the storms, (named Petar), had caused large-scale flooding in Slovenia and Austria, while the other had travelled over United Kingdom from the Atlantic. The path of the combined windstorm was unusual, travelling westwards over the Scandinavian mountain range and thus reaching Norway from the east.

The Norwegian Metheorological Institute forecasted heavy rains, and on 6 August declared an extreme weather event with precipitation expected at between 80 and 100 mm in 24 hours. The Governor of Innlandet (where most of the rain was forecast to fall) set up a crisis management organisation, and all rail traffic on the Dovre, Røros and Rauma lines were pre-emptively cancelled on 7 and 8 August.

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