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Disputation: Trine Jahr Hegdahl

Doctoral candidate Trine Jahr Hegdahl at the Department of Geosciences, Faculty of Mathematics and Natural Sciences, is defending the thesis Hydrological ensemble prediction systems: from evaluating daily streamflow forecasts to exploring the impact of selected flood events in a future climate for the degree of Philosophiae Doctor.

Trine Jahr Hegdahl. Photo: Private

Trine Jahr Hegdahl. Photo: Private

The PhD defence and trial lecture are fully digital and streamed using Zoom. The host of the session will moderate the technicalities while the chair of the defence will moderate the disputation.

Ex auditorio questions: the chair of the defence will invite the audience to ask ex auditorio questions either written or oral. This can be requested by clicking 'Participants -> Raise hand'. 

Trial lecture

As a recording:

How can we predict the future of rivers? Challenges and opportunities to address societal needs

Conferral summary (in Norwegian)

I denne avhandlingen er et rammeverk, tilsvarende systemet for operasjonell flomvarsling i Norge, brukt til å bedre prognoser for flomvarsling, samt å evaluere omfanget av ekstreme flomhendelser i et fremtidsklima. Ved å benytte ensembler og statistiske teknikker ble det laget alternative flomprognoser for 145 nedbørfelt. Disse ble så analysert. Hvor godt flomprognosene traff viste seg å være avhengig av region, sesong og hvilken teknikk som var benyttet for å optimalisere prognosene. Regnflommer om høsten var totalt sett mest utfordrende å varsle. Beregninger av flommer forårsaket av ekstreme nedbørhendelser (her: atmosfæriske elver) viste at enkelthendelsene i et fremtidscenario medførte flom i flere elver samtidig, og at flommene økte i størrelse sammenlignet med dagens flomhendelser.

Main research findings

Popular scientific article about Hegdahl’s dissertation:

Hydrological ensemble prediction systems: from evaluating daily streamflow forecasts to exploring the impact of selected flood events in a future climate

Worldwide, floods are the natural disaster causing the highest economic losses and casualties. Flood warnings are issued to inform of potential threats, and allow flood managing authorities time to take appropriate actions to prevent and reduce the impact. Flood forecasts are often uncertain, and statistical techniques are used to improve the forecasts. Climate studies indicate that flood magnitude and frequency will change. More knowledge to improve flood forecasts and to assess the outcome of future floods is needed.

Image may contain: Water, Water resources, Fluvial landforms of streams, Tree, Plant.
Flooding in Flåm (Aurland, Norway) caused by an atmospheric river in October 2014. Photo: Svein Arne Vågane, NVE


The aim of this thesis is to provide improved operational flood forecasts and raise awareness of future floods. An experimental setup of the Norwegian flood forecasting systems was used and included 145 river catchments. First, techniques to improve flood forecasts were applied and revealed seasonal and regional patterns in flood forecast performance. By exposing areas with low forecast performance, targeted and tailored corrections can be applied. Secondly, extreme flood events caused by atmospheric rivers in a future climate were compared to the most extreme events of the present climate. The future extreme events showed an increase in both flood magnitude and more rivers flooded concurrently.

Photo and other information:

Press photo: Trine Jahr Hegdahl, portrait; 500px. Photo: Private

Other photo material: Figure with description and credit as specified in the article above, size 1000px.

Published Mar. 4, 2021 9:49 AM - Last modified Mar. 16, 2021 3:28 PM