Improved warning thresholds
Klima 2050 has performed a global study of early warning systems (EWS) for debris slides and debris flows, in order to determine weak and strong aspects of the systems in use today, including those in Norway. The Norwegian systems are generally good, but have weaknesses in particular in two fields: improved threshold values for precipitation that trigger slides are needed, and better training of decision makers is needed in relation to how alerts should be handled.
Precipitation thresholds can be estimated by using a number of parameters. Analysis of such parameters calibrated against real historical events provide better insight into which parameters are important. Furthermore, the results also show how extremes, such as e.g. the flooding events in Kvam in 2011 and 2013 strongly affect the estimated threshold values. In order to improve the local warning systems, which is what Norwegian municipalities and owners of critical infrastructure want, the project shows the value of connecting regional, threshold value-based alert with local data. We have shown that e.g. the use of pore pressure data from the same drainage area greatly improves the hit rate of the alerts, even when the instruments are not located close to the landslide path. These results are of great value to the NVE and provide them with important input for improving the early warning service.