Time filter

Source Type

Dibike Y.,Environment Canada | Prowse T.,Environment Canada | Prowse T.,University of Victoria | Saloranta T.,Norwegian Water Resources and Energy Directorate NVE | Ahmed R.,University of Victoria
Hydrological Processes | Year: 2011

The formation and break-up of ice-cover are important seasonal events in mid- to high-latitude cold-region lakes. There is increasing concern regarding how climate change will affect lake-water thermal structure and lake-ice characteristics, particularly ice formation, duration, break-up, thickness, and composition. This study employs a one-dimensional process-based multi-year lake ice model, MyLake, to simulate the evolution of the Northern Hemisphere lake-ice and thermal structure patterns under a changing climate. After testing the model on Baker Lake located in Nunavut Canada, large-scale simulations were conducted over the major land masses of the Northern Hemisphere subarctic regions between 40° and 75°N using hypothetical lakes positioned at 2·5° latitude and longitude resolution. For the baseline period of 1960-1999, the lake-ice model was driven by gridded atmospheric forcings from the ERA-40 global reanalysis data set while atmospheric model forcings corresponding to future (2040-2079) climate were obtained by modifying the ERA-40 data according to the Canadian Global Climate Model projection based on the SRES A2 emissions scenario. Analysis of the modelling results indicates that lake-ice freeze-up timing will be delayed by 5-20 days and break-up will be advanced by approximately 10-30 days, thereby resulting in an overall decrease in lake-ice duration by about 15-50 days. Maximum lake-ice thickness will also be reduced by 10-50 cm. The change in maximum snow depth on the lake-ice ranges between - 15 to + 5 cm, while the change in white-ice thickness ranges between - 20 to + 10 cm depending on the geographic location and other climate parameters. The future warming will also result in an overall increase in lake-water temperature, with summer stratification starting earlier and extending later into the year. © 2011 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.

Engelhardt M.,University of Oslo | Schuler T.V.,University of Oslo | Andreassen L.M.,Norwegian Water Resources and Energy Directorate NVE
Geografiska Annaler, Series A: Physical Geography | Year: 2012

The service seNorge (http://senorge.no) provides gridded temperature and precipitation for mainland Norway. The products are provided as interpolated station measurements on a 1×1km grid. Precipitation gauges are predominantly located at lower elevations such as coastal areas and valleys. Therefore, there are large uncertainties in extrapolating precipitation data to higher altitudes, both due to sparsity of observations as well as the large spatial variability of precipitation in mountainous regions. Using gridded temperature and precipitation data from seNorge, surface mass balance was modeled for five Norwegian glaciers of different size and climate conditions. The model accounts for melting of snow and ice by applying a degree-day approach and considers refreezing assuming a snow depth depended storage. Calculated values are compared to point measurements of glacier winter mass balance. On average for each glacier, modeled and measured surface mass-balance evolutions agree well, but results at individual stake locations show large variability. Two types of problems were identified: first, grid data were not able to capture spatial mass balance variability at smaller glaciers. Second, a significant increase in the bias between model and observations with altitude for one glacier suggested that orographic enhancement of precipitation was not appropriately captured by the gridded interpolation. © 2012 Swedish Society for Anthropology and Geography.

Hamududu B.H.,Norwegian Water Resources and Energy Directorate NVE | Killingtveit A.,Norwegian University of Science and Technology
Energies | Year: 2016

Climate change is altering hydrological processes with varying degrees in various regions of the world and remains a threat to water resources projects in southern Africa. The likely negative impacts of changes in Africa may be worse than in most other regions of the world. This study is an evaluation of the possible impacts of climate change on water resources and hydropower production potential in Kwanza River Basin, Angola. The regional climate data, the basis for future climate scenarios, is used in the hydrological model HBV to assess climate change impacts on water resources in the Kwanza River Basin. Evaluation of changes in hydropower production potential is carried out using an energy model. The simulations show that annual rainfall in 2080 would increase by approximately 16% with increasing inter-annual variability of rainfall and dry season river flow and later onset of the rainy season. The simulation results show that for the Kwanza River Basin the effects as a result of changes in the future climate, in general, will be positive. Consequently, the increase in water resources will lead to increased hydropower production potential in the basin by up to 10%. © 2016 by the authors.

Paul F.,University of Zürich | Andreassen L.M.,Norwegian Water Resources and Energy Directorate NVE | Winsvold S.H.,Norwegian Water Resources and Energy Directorate NVE
Annals of Glaciology | Year: 2011

Pronounced changes in glacier mass and length were observed for the monitored glaciers in the Jostedalsbreen region, Norway, since the last glacier inventories were compiled in the 1960s and 1980s. However, the current overall extent of the glaciers in the region is not well known. To obtain this information, we have compiled a new inventory from two mosaicked Landsat Thematic Mapper (TM) scenes acquired in 2006 that have excellent snow conditions for glacier mapping, the first suitable scenes for this purpose after 22 years of imaging with TM. Drainage divides and topographic inventory parameters were derived from a 25m national digital elevation model for 1450 glaciers. By digitizing glacier outlines from 1 : 50 000 scale topographic maps of 1966, we calculated changes in glacier area for ~300 glaciers. Cumulative length changes for the 1997-2006 period were derived from an additional TM scene and compared with field measurements for nine glaciers. Overall, we find a 9% area loss since 1966, with a clear dependence on glacier size; however, seasonal snow in 1966 in some regions made area determination challenging. The satellite-derived length changes confirmed the observed high spatial variability and were in good agreement with field data (±1 pixel), apart from glacier tongues in cast shadow. The new inventory will be freely available from the Global Land Ice Measurements from Space (GLIMS) glacier database.

Andreassen L.M.,Norwegian Water Resources and Energy Directorate NVE | KJollmoen B.,Norwegian Water Resources and Energy Directorate NVE | Rasmussen A.,University of Washington | Melvold K.,Norwegian Water Resources and Energy Directorate NVE | Nordli O.,Norwegian Meteorological Institute
Journal of Glaciology | Year: 2012

In this paper we document changes of Langfjordjoøkelen, a small ice cap in northern Norway. Surface mass-balance measurements have been carried out on an east-facing part (3.2 km2) of the ice cap since 1989. Measurements reveal a strong thinning; the balance year 2008/09 was the 13th successive year with significant negative annual balance (≤0.30mw.e.). The average annual deficit was 0.9mw.e. over 1989-2009. The recent thinning of Langfjordjkelen is stronger than observed for any other glacier in mainland Norway. Maps from 1966, 1994 and 2008 show that the whole ice cap is shrinking. The total volume loss over 1966-2008 was 0.264km 3. The east-facing part has been greatly reduced in volume (46%), area (38%) and length (20%). For this part over 1994-2008, the cumulative direct mass balance (-14.5mw.e.) is less negative than the geodetic mass balance (-17.7mw.e.). A surface mass-balance model using upper-air meteorological data was used to reconstruct annual balances back to 1948 and to reconstruct unmeasured years 1994 and 1995. Sensitivity of annual balance to 18C warming is -0.76mw.e. and to 10% increase in precipitation is +0.20mw.e.

Skarbovik E.,Norwegian Institute for Agricultural And Environmental Research Bioforsk | Stalnacke P.,Norwegian Institute for Agricultural And Environmental Research Bioforsk | Bogen J.,Norwegian Water Resources and Energy Directorate NVE | Bonsnes T.E.,Norwegian Water Resources and Energy Directorate NVE
Science of the Total Environment | Year: 2012

Reliable estimates of mean concentrations and loads of pollutants in rivers have become increasingly important for management purposes, particularly with the implementation of the European Union Water Framework Directive (WFD). Here, the Numedalslågen River (5500km2) in southern Norway was used as a case study to evaluate the effects of sampling frequency on mean concentrations and estimated loads of suspended particulate matter (SPM). Daily monitoring data from five seasons (April/June-October/November 2001-2005) were analyzed, and three different load estimation techniques were tested: rating curves, linear interpolation, and the ratio method. The reliability of mean SPM concentrations improved with increasing sampling frequency, but even weekly sampling gave error rates as high as 70% in seasons with elevated sediment loads. Load estimates varied considerably depending on both the sampling frequency and the calculation method used. None of the methods provided consistently good results, but the lowest error rate was achieved when using the rating curve on data from fortnightly sampling and additional sampling during floods. Sampling at monthly intervals gave the highest error rates and cannot be recommended for any of the calculation methods applied here. SPM concentrations were correlated (r2>0.5) with arsenic, lead, nickel, orthophosphate, and total phosphorus in the Numedalslågen River. Therefore, the current findings may also have implications for substances other than SPM. The discussion considers examples from actual use of infrequently collected data, and it is advised that managers account for uncertainties in both concentration means and load estimates when assessing the state of a water body or planning mitigation measures. © 2012 Elsevier B.V.

Wilson D.,Norwegian Water Resources and Energy Directorate NVE | Hisdal H.,Norwegian Water Resources and Energy Directorate NVE | Lawrence D.,Norwegian Water Resources and Energy Directorate NVE
Journal of Hydrology | Year: 2010

A pan-Nordic dataset of 151 streamflow records was analysed to detect spatial and temporal changes in streamflow. Prior to undertaking analyses, all streamflow records with significant levels of autocorrelation were pre-whitened to remove the adverse effect of temporal autocorrelation on the test results. The Mann-Kendall trend test was applied to study changes in annual and seasonal streamflow as well as floods and droughts for three periods: 1920-2005, 1941-2005 and 1961-2000. Field significance was evaluated to determine the percentage of stations that are expected to show a trend due to the effect of cross-correlation. The period analysed and the selection of stations influenced the regional patterns found, but the overall picture was that trends of increased streamflow dominate annual values and the winter and spring seasons. Trends identified in summer flows differed between the three periods analysed, whereas no trend was found for the autumn season. In all three periods, a signal towards earlier snowmelt floods was clear, as was the tendency towards more severe summer droughts in southern and eastern Norway. These trends in streamflow result from changes in both temperature and precipitation, but the temperature induced signal is stronger than precipitation influences. This is evident because the observed trends in winter and spring, where snowmelt is the dominant process, are greater than the annual trends. A qualitative comparison of the findings with available streamflow projections for the region showed that the strongest trends found are generally consistent with future changes expected in the projection periods, for example increased winter discharge and earlier snowmelt floods. However, there are predicted changes that are not reflected in past trends, such as the expected increase in autumn discharge in Norway. Hence, the changes expected because of increased temperatures are reflected in the observed trends, whereas changes anticipated due to increases in precipitation are not. © 2010 Elsevier B.V.

Skaugen T.,Norwegian Water Resources and Energy Directorate NVE | Andersen J.,Norwegian Water Resources and Energy Directorate NVE
Hydrological Sciences Journal | Year: 2010

Gridded meteorological data are available for all of Norway as time series dating from 1961. A new way of interpolating precipitation in space from observed values is proposed. Based on the criteria that interpolated precipitation fields in space should be consistent with observed spatial statistics, such as spatial mean, variance and intermittency, spatial fields of precipitation are simulated from a gamma distribution with parameters determined from observed data, adjusted for intermittency. The simulated data are distributed in space, using the spatial pattern derived from kriging. The proposed method is compared to indicator kriging and to the current methodology used for producing gridded precipitation data. Cross-validation gave similar results for the three methods with respect to RMSE, temporal mean and standard deviation, whereas a comparison on estimated spatial variance showed that the new method has a near perfect agreement with observations. Indicator kriging underestimated the spatial variance by 60-80% and the current method produced a significant scatter in its estimates. © 2010 IAHS Press.

Lind A.,Institute for Energy Technology of Norway | Rosenberg E.,Institute for Energy Technology of Norway | Seljom P.,Institute for Energy Technology of Norway | Espegren K.,Institute for Energy Technology of Norway | And 2 more authors.
Energy Policy | Year: 2013

The EU renewable energy (RES) directive sets a target of increasing the share of renewable energy used in the EU to 20% by 2020. The Norwegian goal for the share of renewable energy in 2020 is 67.5%, an increase from 60.1% in 2005. The Norwegian power production is almost solely based on renewable resources and the possibility to change from fossil power plants to renewable power production is almost non-existing. Therefore other measures have to be taken to fulfil the RES directive. Possible ways for Norway to reach its target for 2020 are analysed with a technology-rich, bottom-up energy system model (TIMES-Norway). This new model is developed with a high time resolution among others to be able to analyse intermittent power production. Model results indicate that the RES target can be achieved with a diversity of options including investments in hydropower, wind power, high-voltage power lines for export, various heat pump technologies, energy efficiency measures and increased use of biodiesel in the transportation sector. Hence, it is optimal to invest in a portfolio of technology choices in order to satisfy the RES directive, and not one single technology in one energy sector. © 2013 Elsevier Ltd.

Melvold K.,Norwegian Water Resources and Energy Directorate NVE | Skaugen T.,Norwegian Water Resources and Energy Directorate NVE
Annals of Glaciology | Year: 2013

This study presents results from an Airborne Laser Scanning (ALS) mapping survey of snow depth on the mountain plateau Hardangervidda, Norway, in 2008 and 2009 at the approximate time of maximum snow accumulation during the winter. The spatial extent of the survey area is >240km2. Large variability is found for snow depth at a local scale (2 m2), and similar spatial patterns in accumulation are found between 2008 and 2009. The local snow-depth measurements were aggregated by averaging to produce new datasets at 10, 50, 100, 250 and 500 m2 and 1 km2 resolution. The measured values at 1 km2 were compared with simulated snow depth from the seNorge snow model (www.senorge.no), which is run on a 1 km2 grid resolution. Results show that the spatial variability decreases as the scale increases. At a scale of about 500 m2 to 1 km2 the variability of snow depth is somewhat larger than that modeled by seNorge. This analysis shows that (1) the regional-scale spatial pattern of snow distribution is well captured by the seNorge model and (2) relatively large differences in snow depth between the measured and modeled values are present.

Loading Norwegian Water Resources and Energy Directorate NVE collaborators
Loading Norwegian Water Resources and Energy Directorate NVE collaborators