Assessing the relationship between short-term meteorological variability and the timing of GLOFs in Norway based on 83 documented events

While the influence of long-term climatic warming on glacier lake outburst floods (GLOF) occurrence is well-documented, the role of short-term meteorological conditions in influencing the precise timing of individual outburst events remains poorly understood. This gap is particularly evident in the Scandinavian region, where only few studies have examined how variability in temperature, precipitation, and melt conditions during days and weeks prior to an outburst flood may influence the timing of GLOF events. Therefore, this study aims to systematically investigate the relationship between the short-term variability in key meteorological variables and the timing of mostly ice-dammed GLOF events in Norway. Of the 112 documented GLOF events in Norway between 1979 and 2025, only 83 were selected for further analysis, as precise event dates were not available for all documented outburst floods. Meteorological variables for all individual GLOF events were extracted using the NORA3 dataset, a reanalysis product provided by the Norwegian Meteorological Institute. Time windows of 60, 30, 15, 7, and 3 days prior to each event were defined to assess short-term changes in meteorological conditions leading up to the outburst floods. The analysis shows no clear general relationship between precipitation and timing of GLOF events. However, in a few cases, intense precipitation immediately prior to the outburst may have acted as a triggering factor. Regarding temperature development prior to the outburst events across different time windows, the analysis revealed an inverse relationship: Significant warming trends are more prevalent over longer periods preceding an outburst, whereas shorter-term windows are dominated by non-significant or negative temperature trends. A quite similar pattern was observed regarding the change of the mean average temperatures across the different time windows. Comparing the 7 days immediately prior to an outburst with the preceding 60 days, mean temperatures were higher in 66.3 % of events. In contrast, when considering the 3 days prior compared to the preceding 30 days, only 49.4 % of events were warmer. These findings suggest that short-term warming immediately before GLOFs does not follow a consistent pattern. Regarding total water input (melt and precipitation), the analysis shows no evidence of a systematic short-term increase immediately prior to outbursts. While longer periods (e.g., 15 days) preceding events often had higher cumulative input compared to earlier intervals, the proportion of events with higher input decreased for shorter time windows. Furthermore, snow cover at the glacier margins was analyzed using satellite data, revealing that the majority (54%) of glaciers remained snow-covered both before and after the outburst events. The analysis shows that no single trigger can be identified in most cases, but that a minimum amount of meltwater input combined with short-term cooling may be a combination of conditions that frequently precedes outburst floods at ice-dammed lakes in Norway.