Heavy rainfall events in Svalbard

Top image: Ola Aashamar has written a master’s thesis in connection with the Alertness project. Here he is on fieldwork at the precipitation station in Tempelfjorden. Photo: Eirik Aasmo Finne.

In a master’s thesis recently completed at the University of Oslo and the University Center in Svalbard (UNIS), Ola Aashamar has studied how well strong precipitation events at Svalbard are represented in the weather model AROME-Arctic.

23 October 2019
Text: Anna Kathinka Dalland Evans/ The Norwegian Meteorological Institute

In the study, Aashamar has used both measurements from the Meteorological Institute and measurements he himself collected during the summer of 2018. Aashamar has worked on the thesis in collaboration with the research project Alertness, which is managed by the Meteorological Institute.

– Alertness is a good example of a successful interaction between the academic university environment and weather forecasting services, says UNIS associate professor Marius Jonassen, who has been Aashamar’s main supervisor during the master’s thesis.
– As part of this interaction, we involve and support researchers in Alertness master students with relevant projects. Ola’s project is a good example of this, he continues.

The title of the thesis is Heavy Rain Events in Svalbard Summer and Autumn of 2016 to 2018.

Heavy rainfall in the summer (June-November) has the potential to affect both nature and infrastructure in Svalbard. A good example of this is the heavy rainfall events that occurred in Svalbard in the fall of 2016, where roads in Longyearbyen were blocked by landslides and residents were evacuated due to mudslide hazards. The Svalbard 2100 report from the Norwegian Climate Services Center states that heavy rainfall events on Svalbard are likely to occur more frequently and become more intense in a changing climate in the coming century.

A weather forecasting model that manages to predict such incidents in Svalbard will therefore only become more important in the years to come. – In my master thesis, I have therefore looked into how well the weather forecast model AROME-Arctic has managed to predict the strongest precipitation episodes in Svalbard in the summer. I have studied the years the model has been operational (June-November, 2016-2018), explains Ola Aashamar.

He has compared precipitation forecasts from AROME-Arctic with the observed rainfall from the Meteorological Institute’s weather stations in Svalbard.

When south westerly winds bring moist and warm air northward and hit the mountains on the west coast of Spitsbergen, precipitation is often enhanced. This is not unlike the type of weather that people in western Norway often experience.

– For such precipitation cases, my results show that the model often reports too little rainfall at the stations on the west coast of Svalbard (Hornsund, Isfjord Radio and Ny-Ålesund), while it generally reports too much in the central areas around Longyearbyen. However, in cases of heavy rainfall with wind from the east or southeast, the model generally reports too little rain in Longyearbyen and too much on the west coast stations, Aashamar says.

Thanks to support from, among others, the Alertness project, a field work was also carried out in connection with the project, where he measured rainfall in the area around Longyearbyen and in Tempelfjorden, where few meteorological observations have been made in the past. The fieldwork resulted in several interesting measurements; relatively strong showers (up to 5 mm per hour), a link between large-scale wind fields and over- or underestimation of precipitation in the model, and observation of increased precipitation with terrain height (~ 10% increase per 100 m).

The results from the fieldwork show that even simple field campaigns in the summer season on Svalbard can provide a better understanding of both rainfall in Svalbard in general and the characteristics of weather models in areas with few measurements and observations.

Facts about the Alertness project
Alertness  (Advanced models and weather prediction in the Arctic) is a 4-year research project about Arctic weather prediction, financed by the Research Council of Norway.
Alertness is led by the Norwegian Meteorological Institute (MET Norway) and is a cooperation between MET Norway, University of Bergen, NORCE, University of Tromsø , the Royal Netherlands Meteorological Institute, the Nansen Environmental and Remote Sensing Center (NERSC) and the University Centre in Svalbard (UNIS).

Alertness is endorsed by the Year of Polar Prediction (YOPP).