Abstract
We apply a physical climate storyline approach to an autumn flood event in the West Coast of Norway caused by an atmospheric river to demonstrate the value and challenges of higher spatial and temporal resolution in simulating flood impacts. We use a modelling chain whose outputs are familiar and used operationally, for example to issue flood warnings. With two different versions of a hydrological model, we show that (1) the higher spatial resolution between the global and regional climate model is necessary to realistically simulate the high spatial variability of precipitation in this mountainous region and (2) only with hourly data are we able to capture the fast flood-generating processes leading to the peak streamflow. The 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 much larger than a present one, in others no event occurs as the atmospheric river simply does not hit that catchment. The use of an operational flood warning system for future events is expected to facilitate stakeholder engagement.
Highlights
Between the 27th and 29th of October 2014, large amounts of pre cipitation - up to 300 mm in less than 5 days in some areas - fell over the West Coast of Norway, causing floods and damages in several valleys (Lussana et al, 2018)
After consulting a range of users and stakeholders, the autumn floods of September 2005 and October 2014, both caused by an atmospheric river hitting the West Coast of Norway, were chosen as a typical event for this physical climate storyline study
We investigate the impact of having higher spatial and temporal resolution for the simulation of peak flows in two catchments
Summary
Between the 27th and 29th of October 2014, large amounts of pre cipitation - up to 300 mm in less than 5 days in some areas - fell over the West Coast of Norway, causing floods and damages in several valleys (Lussana et al, 2018). The large amounts of rain in October 2014 were caused by the passage of such an atmospheric river (Lussana et al, 2018 and SI Fig. 2a). Atmospheric rivers are long and narrow regions of intense water vapour transport in the lower atmo sphere and Sodemann and Stohl (2013) and Azad and Sorteberg (2017) have shown how important they are to transport sub- and extratropical moisture to the West Coast of Norway. Atmospheric rivers are long and narrow regions of intense water vapour transport in the lower atmo sphere and Sodemann and Stohl (2013) and Azad and Sorteberg (2017) have shown how important they are to transport sub- and extratropical moisture to the West Coast of Norway. Benedict et al (2019a) further showed that atmospheric rivers are associated with more than 85% of extreme precipitation in this region for the period September–March from 1979 to 2014
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