Site specific avalanche warning for settlements in Northern Norway: Twenty years of the Northern Norway Avalanche Surveillance Program

Abstract

Northern Norway experienced an intensely snow rich winter in 1997 when settled snow heights reached a record 240 cm at the weather station in Tromsø on April 29th. Numerous avalanches, settlement evacuations, and two fatalities in a destroyed house in the settlement of Breivikeidet left the public exhausted at the end of the winter. The chaotic response to avalanche events during the season demonstrated the need for local and regional authorities to adopt a more proactive and coordinated approach to manage avalanche risk. Hazard mapping was initialized to gain an overview over the exposed settlements and to pinpoint the buildings at risk. At the same time, an avalanche warning service (Northern Norway Avalanche Surveillance; ‘Nordnorsk skredovervåkning’, NNSO) was established in the winter 2002/2003 by initiative of Tromsø municipality, the Norwegian Geotechnical Institute (NGI) in cooperation with Tromsø police office and the County Governor in Troms. Several other municipalities joined the initiative, and an inter-municipal organization led by Tromsø municipality was formed. At maximum, 16 municipalities encompassing 41 settlements from North Cape to Lofoten, a distance of 600 km, were covered by the warning system. The Meteorological Institute in Tromsø provided weather surveillance and NGI in Oslo supplied avalanche expertise. Meteorologists in Tromsø used threshold criteria in snowfall and winds to alert the avalanche forecasters in Oslo to provide an avalanche hazard assessment. The expert assessment relied heavily on local observers who assisted with daily snow height and new snow measurements and supply of profound knowledge of each settlement’s avalanche history and local climate. If necessary, evacuations were enforced by the police, assisted by the municipalities. The system provided systematic risk management and a sense of safety for over 20 years. The simple setup of the system showed excellent performance over many years at minimal costs. In recent years, new methods, updated hazard maps, dataflow and establishment of regional avalanche warning have warranted revisions to the established system. After the resignation of Tromsø municipality as the project coordinator (2022), today only six municipalities remain in the system under the lead of Kåfjord municipality. They have applied for a regional research project to support the further development of the NNSO as they consider the system vital for the safety of their inhabitants. This project exemplifies how remote, resource-limited communities can develop simple and cost-efficient site-specific avalanche warning services.