Geographic variation and temporal trends in ice phenology in Norwegian lakes over a century

Observations from 1890 to 2020 of ice phenology for 101 Norwegian lakes were used to detect variation in ice phenology. The average date of ice break-up occurred later in spring with increasing altitude, latitude and longitude. The average date of freeze-up and the length of the ice-free period decreased with altitude and longitude. Lakes were completely frozen later recently later in autumn. A significant trend for earlier break-up, later freeze-up and completely frozen lakes after 1991

Naturfareforum : årsrapport 2019

I denne rapporten er aktivitetene og ressursbruken i Naturfareforum 2019 oppsummer

Uncertainty introduced by flood frequency analysis in projections for changes in flood magnitudes under a future climate in Norway

Study region: The study considers 115 unregulated catchments in Norway, with areas from 6 to 15,449 km2 and flood generation regimes ranging from snowmelt-dominated to ‘mixed’ (snow-melt and rainfall) to fully rainfall-driven. Study focus: Bias-corrected EURO-CORDEX RCM output for RCP 8.5 is used to generate an ensemble of 500 hydrological simulations for assessing changes in flood magnitudes under a future climate. Flood estimates are based on three extreme value distributions (EVDs), Gumbel, Generalised Extreme Value and Generalised Pareto, with confidence intervals calculated using parametric bootstrapping, and uncertainty introduced into the ensemble by the flood estimation is evaluated using variance decomposition. Changes in EVD parameters under future conditions are also assessed. New hydrologic insight for the region: There are large differences in projected changes between catchments, with median estimates ranging from −48 % to +99 % for the 200 year flood. Flood magnitudes in all catchments with rainfall-dominant or mixed flood regimes are expected to increase. EVDs with a shape parameter (GEV and GPD) indicate larger increases in higher flood quantiles than the Gumbel distribution (e.g. by 5–8 percentage points for the 200 year flood). Flood frequency estimation contributes 30–52 % of the total ensemble range in individual catchments. Location and scale parameters generally increase in catchments with increasing flood magnitudes, and some catchments with mixed flood regimes also exhibit increases in the shape parameter under future conditions

Glaciological investigations in Norway 2019

Results of glaciological investigations performed at Norwegian glaciers in 2019 are presented in this report. The main part concerns mass balance investigations. Results from investigations of glacier length changes are discussed in a separate chapter

Styringssystem for omløpsventilar

Med grunnlagsdata frå drift av fire små kraftverk er det laga eit generelt styringsverktøy for alle kraftverk med omløpsventil. Kravet er at vasstanden nedstraums kraftverket ikkje skal være raskare enn 10 cm/t. Denne rapporten presenterer valideringsforsøk på fire kraftverk av den teoretiske modellen. Resultata er gode der programmeringa er gjort korrekt og nytta grunnlagsdata er av god kvalitet

Present and future changes in winter climate indices relevant for access disruptions in Troms, northern Norway

A number of seaside communities in Troms, northern Norway, are vulnerable to sudden weather-induced access disruptions due to high-impact weather and dependency on one or few roads. In this paper we study changes in winter weather known to potentially cause access disruptions in Troms, for the present climate (1958–2017) and two future periods (2041–2070; 2071–2100). We focus on climate indices associated with snow avalanches and weather that may lead to for example slippery road conditions. In two focus areas, the most important results show larger snow amounts now compared to 50 years ago, and heavy snowfall has become more intense and frequent. This trend is expected to turn in the future, particularly at low elevations where snow cover during winter might become a rarity by 2100. Strong snow drift, due to a combination of snowfall and wind speed, has slightly increased in the two focus areas, but a strong decrease is expected in the future due to less snow. Events of heavy rain during winter are rather infrequent in the present winter climate of Troms, but we show that these events are likely to occur much more often in all regions in the future

Test av styringssystem for omløpsventilar

NVE ønsket å få undersøkt om omløpsventiler blir driftet i henhold til intensjonene. To småkraftverk på hver side av Hardangerfjorden, Vestland, ble valg ut for å teste et nyutviklet styringssystem. SWECO Norge AS gjennomførte denne testen av styringssystemet som de har utviklet på bakgrunn av erfaring med ni andre småkraftverk. Resultatene fra testen med de to kraftverkene viser at styringssystemet er klar for bruk. Denne rapporten må sees i sammenheng med tidligere publiserte rapporter fra prosjektet og spesielt NVE Ekstern rapport 2019-63

Glacier change in Norway since the 1960s – an overview of mass balance, area, length and surface elevation changes

In this paper, we give an overview of changes in area, length, surface elevation and mass balance of glaciers in mainland Norway since the 1960s. Frontal advances have been recorded in all regions except the northernmost glaciers in Troms and Finnmark (Storsteinsfjellbreen, Lyngen and Langfjordjøkelen). More than half of the observed glaciers, 27 of 49, had marked advances in the 1990s. The glaciological mass-balance values for the period 1962–2018, where 43 glaciers have been measured, show great inter-annual variability. The results reveal accelerated deficit since 2000, the most negative decade being 2001–2010. Some years with a positive mass balance (or less negative) after 2010s can be attributed to variations in large-scale atmospheric circulation. A surface elevation change and geodetic mass balance were calculated for a sample of 131 glaciers covering 817 km2 in the ‘1960s’ and 734 km2 in the ‘2010s’, giving an area reduction of 84 km2, or 10%. The sample covers many of the largest glaciers in Norway, and they had an overall change in surface elevation of −15.5 m for the ~50 year period. Converted to a geodetic mass balance this gives a mean mass balance of −0.27 ± 0.05 m w.e. a−1

An Event-Based Approach to Explore Selected Present and Future Atmospheric River–Induced Floods in Western Norway

The aim of this study is to investigate extreme precipitation events caused by atmospheric rivers and compare their flood impact in a warmer climate to current climate using an event-based storyline approach. The study was set up by selecting four high-precipitation events from 30 years of present and future climate simulations of the high-resolution global climate model EC-Earth. The two most extreme precipitation events within the selection area for the present and future climate were identified, and EC-Earth was rerun creating 10 perturbed realizations for each event. All realizations were further downscaled with the regional weather prediction model, AROME-MetCoOp. The events were thereafter used as input to the operational Norwegian flood-forecasting model for 37 selected catchments in western Norway, and the magnitude and the spatial pattern of floods were analyzed. The role of the hydrological initial conditions, which are important for the total flooding, were analyzed with a special emphasis on snow and soil moisture excess. The results show that the selected future extreme precipitation events affected more catchments with larger floods, compared to the events from present climate. In addition, multiple realizations of the meteorological forcing and four different hydrological initial conditions, for example, soil saturation and snow storage, were important for the estimation of the maximum flood level. The meteorological forcing (e.g., the internal variability/perturbed output) accounts for the highest contribution to the spread in flood magnitude; however, for some events and catchments the hydrological initial conditions affected the magnitudes of floods more than the meteorological forcing

Impacts of hydrological model calibration on projected hydrological changes under climate change – a multi-model assessment in three large river basins

This study aimed to investigate the influence of hydrological model calibration/validation on discharge projections for three large river basins (the Rhine, Upper Mississippi and Upper Yellow). Three hydrological models (HMs), which have been firstly calibrated against the monthly discharge at the outlet of each basin (simple calibration), were re-calibrated against the daily discharge at the outlet and intermediate gauges under contrast climate conditions simultaneously (enhanced calibration). In addition, the models were validated in terms of hydrological indicators of interest (median, low and high flows) as well as actual evapotranspiration in the historical period. The models calibrated using both calibration methods were then driven by the same bias corrected climate projections from five global circulation models (GCMs) under four Representative Concentration Pathway scenarios (RCPs). The hydrological changes of the indicators were represented by the ensemble median, ensemble mean and ensemble weighted means of all combinations of HMs and GCMs under each RCP. The results showed moderate (5–10%) to strong influence (> 10%) of the calibration methods on the ensemble medians/means for the Mississippi, minor to moderate (up to 10%) influence for the Yellow and minor (< 5%) influence for the Rhine. In addition, the enhanced calibration/validation method reduced the shares of uncertainty related to HMs for three indicators in all basins when the strict weighting method was used. It also showed that the successful enhanced calibration had the potential to reduce the uncertainty of hydrological projections, especially when the HM uncertainty was significant after the simple calibration