– The figures show that we get more and bigger floods than the statistics would indicate in a stable climate. So says Kjersti Daae, associate professor in physical oceanography at the University of Bergen and the Bjerknes Center for Climate Research. Since 2012 she has been researching climate, and since 2011 she herself has lived in Voss. At the weekend, she could see through the window that the water level rose by around six metres. – We live in a time with much more rainfall. We really get climate change right in the face here, says Voss mayor Hans-Erik Ringkjøb. No one was injured in the storm, but the damage could cost up to NOK 100 million. Climate researcher: This is how temperature and floods are connected Daae has extracted figures from NVE. They have a measurement point at Bulken på Voss, near the outlet of Lake Vangsvatnet. The figures show that on Voss there have been five floods that exceeded the 20-year flood level in the last eight years. Floods on Voss This overview shows the five worst floods on Voss in the last eight years. The overview here taken from NVE’s measuring point Bulken (62.5) in their database sildre.nve.no. NVE measures floods in water flow, which shows how much water leaves the river Vosso from Vangsvatnet. This is given in cubic meters per second. One cubic meter of water is 1000 litres. A standard bathtub holds around 160 litres. Floods above the level for the 20-year flood on Voss in the last eight years: 28 October 2014: 813 m3/s 12 November 2022: 769 m3/s 15 October 2018: 644 m3/s 21 December 2015: 629 m3/s 19 November 2018: 603 m3/s NVE has calculated definitions of flooding at the point on Bulken. Normal highest water flow value during a year: 400 m3/s 5-year flood: 470 m3/s 10-year flood: 530 m3/s 20-year flood: 580 m3/s 50-year flood: 660 m3/s 100-year flood: 720 m3/s 200-year flood: 780 m3/s 500-year flood: 880 m3/s 1000-year flood: 960 m3/s In the future, NVE believes that there will be 40 percent more water as a result of climate change. This is partly because, with higher temperatures in autumn and winter, the risk of getting rain instead of snow high up in the mountains increases. Therefore, the flood values will change as follows: Normal highest water flow value during a year: 560 m3/s 5-year flood: 660 m3/s 10-year flood: 740 m3/s 20-year flood: 820 m3/s 50-year flood: 920 m3 /s 100-year flood: 1010 m3/s 200-year flood: 1100 m3/s 500-year flood: 1230 m3/s 1000-year flood: 1340 m3/s “Given this, what is calculated in today’s climate becomes a 200- annual flood in tomorrow’s climate (towards the year 2100) a 20 – 50-year flood”, writes NVE. On the night of Saturday, you approached the level of a 200-year flood, for the second time since 2014. – A 20-year flood can mean that within a year there is a one-twentieth chance of such a flood, or that it is likely that we will have one such a flood in 20 years. Now there have been five such in eight years, says Daae. RESEARCHER: Climate researcher Kjersti Daae at the University of Bergen and the Bjerknes Center. Photo: Oddgeir Øystese / news There are four main reasons why higher temperatures lead to more frequent and larger floods, Daae explains: Warmer air can hold more moisture. The low pressures can bring larger amounts of water with them. When the ocean gets warmer, evaporation happens faster. This makes more water vapor available to create precipitation. Due to more efficient evaporation in a warmer climate, storms gain more energy and become larger and more powerful. This means that we can expect several strong storm systems to hit the Norwegian coast. Winters are getting shorter. This makes the autumn seasons and flood seasons longer. In winter, the precipitation comes as snow in the mountains, and we thus avoid large rainfall floods. WATER: On the night of Saturday, the water flow was at its highest. Then it approached the level for the 200-year flood on Voss. Photo: Tim Tønnessen / Tim Tønnessen I think a 200-year flood can happen every twenty years – Voss has had another big flood, Erik Holmqvist, hydrologist at NVE. He is the one who created the reports that define the levels for flooding. In the calculation for the river Vosso written in 2015, Holmqvist writes that the floods will only increase in size in the future. For Voss, it is expected that flood water flows will increase by 40 per cent in the year 2100. – This means that what was a 200-year flood in the climate we have been used to will occur more frequently in the climate of the future. This is what we are now beginning to see. In the report, Holmqvist writes that what we have been used to as a 200-year flood will be a 20-50-year flood in 2100. FLOODS: – We live in a time with much more precipitation. We really get climate change right in the face here, says Voss mayor Hans-Erik Ringkjøb. Photo: Sjur Mikal Dolve / news – If it’s full, then it’s full Climate researcher Hans Olav Hygen at the Meteorological Institute says that the precipitation started on Voss on Thursday afternoon, and lasted until Friday afternoon. Then there was a steady amount of rain, with 4.9 millimeters around midnight on Friday as the highest hourly measurement. Since it had also been raining steadily for several days in advance, many ditches and streams were already well filled with water. Thus, the precipitation on Thursday and Friday had no other way to go than over the banks of Lake Vangsvatnet. – All magazines have their limits. When it’s full, it’s full, says Hygen.
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