With increasing temperatures in Norway, the possibility of heat waves are assumed to increase. The Norwegian Meteorological Institute (MET Norway) is testing ways to monitor heat waves and possibly implement an operational warning system for heat waves in the future. For this work, it was necessary to assess the development of observed heat waves in Norway.
Heat waves were computed from daily minimum and maximum temperatures for the period 1961-2020, for three example stations and maps. For the stations, time series were assessed. For the maps, an observation-based dataset on a 1×1 km grid was used. The two different normal periods 1961-1990 and 1991-2020 were also compared.
The method to qualify a heat wave determines the number of heat waves in a given summer. There are different methods used internationally. MET Norway wants to find a method that works for Norway, and maybe in cooperation with surrounding countries. The last couple of years we have had the same criterias as used in Denmark; the mean value of maximum temperature of three consecutive days ≥ 28 degrees. In this study we have looked at different methods to qualify a heat wave in Norway, since the Danish method indicated heat waves too frequently, also during the spring. The method for heat waves is based on the maximum and minimum temperature combined. We have looked at different temperature limits and different number of days. For other weather warnings, a 2 years return period is used for a yellow warning. When testing different methods, we found that the mean value of maximum temperature for 5 days ≥ 28 degrees combined with the mean value of minimum temperature for 5 days ≥ 16 degrees were likely to occur seldom enough and also give some heat stress to people and nature.
Climate services has worked together with the forecasting group at MET Norway to propose a method to use for both forecasting and climatology. This summer (2022) the heat wave monitoring system will be tested operationally, and an evaluation is due in the autumn.
How to cite: Tilley Tajet, H. T., Sagen, S., Agersten, S., Hygen, H. O., Gangstø Skaland, R., Lussana, C., Brox Nilsen, I., and Smits, J.: Climatological Heat Waves in Norway - a base for Operational Warning System, EMS Annual Meeting 2022, Bonn, Germany, 5–9 Sep 2022, EMS2022-344, https://doi.org/10.5194/ems2022-344, 2022.
