Climate change projections clearly indicate that heavy precipitation events will increase particularly in higher northern latitudes. Large-scale dynamical processes, such as atmospheric rivers that evolve from extra-tropical cyclones and cause anomalous strong orographic rainfall, are characteristic for flood events at the west coast of Norway. Recent high-impact flood events in Norway have emphasized the need for more proactive climate change adaptation. This requires local, actionable and reliable climate information to support the decision making as well as awareness and consideration of barriers to adaptation.
The project started with a kick-off meeting in Oslo in September 2016, where we selected extreme weather events (the October flood in Bergen 2005 and Flåm 2014) for which we applied the "Tales of Future Weather" approach. We arranged so far two stakeholder workshops (November 2016 and April 2018, see https://www.cicero.oslo.no/en/TWEX/publications-and-events_twex) to get feedback on relevant extreme events and needs for decision making. In the second stakeholder workshop, we presented TWEX results and discussed how to communicate the outcomes of our climate and hydrological model simulations.
From April 24th-26th 2019, we held an international workshop on physical modelling supporting a ?storyline approach? at the Oslo Science Park. Around 40 international researchers gathered to discuss current approaches to generate event-based storylines using physical modelling and explore how they can be most effectively integrated into the wider climate information landscape in a way that helps climate communication and policies (reported in CICERO policy note 2019:1).
We have done a literature review of barriers to adapt to extreme events, with a focus on general barriers to adaptation and municipal barriers to adapt to extreme events. The literature review provided background for field work preparation. The field work took place in Western Norway in October 2017 and the purpose was to gain a deeper understanding of adaptation measures to extreme events in selected localities, learn from recent events and identify barriers to adaptation.
One part of the project was dedicated to understanding the large-scale circulation the leads to heavy precipitation events in the West Coast of Norway, the so-called ?atmospheric rivers?. We found that more than 80% of flood events in Norway are caused by these atmospheric rivers, which are narrow corridors of large water vapour amounts in the atmosphere. The most important insight is that the heavy precipitation that falls over the West Coast of Norway in the cold season will increasingly fall as rain rather than snow with increasing global warming. Using a higher resolution regional atmospheric model captures the fact that with the passage of an atmospheric river, some valleys receive high amounts of precipitation and others not, while the coarser resolution global model shows uniform precipitation in the whole region. Translating the event into the future leads to similar results: while in some catchments, a future flood might be 50% larger than a present one (e.g. in Røykenes), in others no event occurs as the atmospheric river simply does not hit that catchment (e.g. in Flåm).
Using the operational flood forecasting system of NVE, we found that the future atmospheric river events affect larger areas compared to the present events, meaning the future events caused floods in more catchments at the same time, and the floods were at a higher magnitude. As each event is unique, the landfall of the atmospheric rivers is difficult to determine beforehand. Hence, applying hydrological modelling to several catchments within a larger area was important to capture the total spatial flood impact of each event. Furthermore, hydrological initial conditions, e.g. soil saturation and snow storage, affected the flood magnitude for most of the catchments and for all events.
The benefit of the event-based approach is that the events are easier to visualize and to communicate, than for example multi-model ensemble probabilities. The event-based approach is therefore useful to raise the awareness of possible future flood impacts. Floods, often accompanied by landslides, are demanding situations for rescue and emergency preparedness. By providing information that implies that future events most likely will affect more catchments at the same time, and hence involve more municipalities simultaneously, can reveal some future challenges for e.g. municipalities, railway- and road authorities. We find that a key barrier to proactive adaptation is the perceived need (or lack thereof) to adapt. For instance, the municipality hit by a very severe flood assume not to be hit by such an extreme event again in the near future. Other municipalities feel already sufficiently protected, because either their areas were not directly affected, or have been secured after the event.
Recent high-impact flood events in Norway have emphasized the need for more proactive climate change adaptation. This requires local, actionable and reliable climate information to support the decision making as well as awareness and consideration of barriers to adaptation. Thus, a seamless chain from global climate system modelling over high resolution hydrological modelling to impact assessments is needed. TWEX-Future.no will address these challenges by taking a novel "Tales of future weather" approach. This approach suggests that scenarios tailored to a specific region and stakeholder in combination with numerical weather prediction models will offer a more realistic picture of what future weather might look like, hence facilitating adaptation planning and implementation.
Climate change projections clearly indicate that heavy precipitation events will increase particularly in higher northern latitudes. Large-scale dynamical processes, such as atmospheric rivers that evolve from extra-tropical cyclones and cause anomalous strong orographic rainfall are characteristic for flood events at the west coast of Norway. To capture such events in realistic details, the current approach of downscaling coarse-resolution global climate model simulations has critical shortcomings.
In TWEX-Future.no, we will use case studies of high-impact flood events selected jointly with Norwegian stakeholders, such as Statkraft, and perform a holistic autopsy of the events (physical hazard, vulnerability, and barriers to adaptation). Selected events will then be simulated in the present and future using a combination of high-resolution global Earth system models and regional Numerical Weather Prediction models, while maintaining the stakeholder's operational chain for analyzing the impacts of the event in the future. This will provide a valuable basis to explore, in a Norwegian context, whether the "Tales of Future Weather" approach offers added-value to current practice.