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  • 121.
    Koenigk, Torben
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Berg, Peter
    SMHI, Forskningsavdelningen, Hydrologi.
    Doescher, Ralf
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Arctic climate change in an ensemble of regional CORDEX simulations2015Ingår i: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 34, artikel-id 24603Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fifth phase Climate Model Intercomparison Project historical and scenario simulations from four global climate models (GCMs) using the Representative Concentration Pathways greenhouse gas concentration trajectories RCP4.5 and RCP8.5 are downscaled over the Arctic with the regional Rossby Centre Atmosphere model (RCA). The regional model simulations largely reflect the circulation bias patterns of the driving global models in the historical period, indicating the importance of lateral and lower boundary conditions. However, local differences occur as a reduced winter 2-m air temperature bias over the Arctic Ocean and increased cold biases over land areas in RCA. The projected changes are dominated by a strong warming in the Arctic, exceeding 15 degrees K in autumn and winter over the Arctic Ocean in RCP8.5, strongly increased precipitation and reduced sea-level pressure. Near-surface temperature and precipitation are linearly related in the Arctic. The wintertime inversion strength is reduced, leading to a less stable stratification of the Arctic atmosphere. The diurnal temperature range is reduced in all seasons. The large-scale change patterns are dominated by the surface and lateral boundary conditions so future response is similar in RCA and the driving global models. However, the warming over the Arctic Ocean is smaller in RCA; the warming over land is larger in winter and spring but smaller in summer. The future response of winter cloud cover is opposite in RCA and the GCMs. Precipitation changes in RCA are much larger during summer than in the global models and more small-scale change patterns occur.

  • 122.
    Pechlivanidis, Ilias
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Olsson, Jonas
    SMHI, Forskningsavdelningen, Hydrologi.
    Sharma, D.
    Bosshard, Thomas
    SMHI, Forskningsavdelningen, Hydrologi.
    Sharma, K. C.
    ASSESSMENT OF THE CLIMATE CHANGE IMPACTS ON THE WATER RESOURCES OF THE LUNI REGION, INDIA2015Ingår i: GLOBAL NEST JOURNAL, ISSN 1790-7632, Vol. 17, nr 1, s. 29-40Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate change is expected to have a strong impact on water resources at the local, regional and global scales. In this study, the impact of climate change on the hydro-climatology of the Luni region, India, is investigated by comparing statistics of current and projected future fluxes resulting from three representative concentration pathways (RCP2.6, RCP4.5, and RCP8.5). The use of different scenarios allows for the estimation of uncertainty of future impacts. The projections are based on the CORDEX-South Asia framework and are bias-corrected using the DBS method before being entered into the HYPE (HYdrological Predictions for the Environment) hydrological model to generate predictions of runoff, evapotranspiration, soil moisture deficit, and applied irrigation water to soil. Overall, the high uncertainty in the climate projections is propagated in the impact model, and as a result the spatiotemporal distribution of change is subject to the climate change scenario. In general, for all scenarios, results show a -20 to +20% change in the long-term average precipitation and evapotranspiration, whereas more pronounced impacts are expected for runoff (-40 to +40% change). Climate change can also affect other hydro-climatic components, however, at a lower impact. Finally, the flow dynamics in the Luni River are substantially affected in terms of shape and magnitude.

  • 123. Fosser, G.
    et al.
    Khodayar, S.
    Berg, Peter
    SMHI, Forskningsavdelningen, Hydrologi.
    Benefit of convection permitting climate model simulations in the representation of convective precipitation2015Ingår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 44, nr 1-2, s. 45-60Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A major source of uncertainty in regional climate model (RCM) simulations arises from the parameterisation of sub-grid scale convection. With increasing model resolution, approaching the so-called convection permitting scale, it is possible to switch off most of the convection parameterisations. A set of simulations using COSMO-CLM model has been carried out at different resolutions in order to investigate possible improvements and limitations resulting from increased horizontal resolution. For our analysis, 30 years were simulated in a triple nesting setup with 50, 7 and 2.8 km resolutions, with ERA40 reanalysis data at the lateral boundaries of the coarsest nest. The investigation area covers the state of Baden-Wurttemberg in southwestern Germany, which is a region known for abundant orographically induced convective precipitation. A very dense network of high temporal resolution rain gauges is used for evaluation of the model simulations. The purpose of this study is to examine the differences between the 7 and 2.8 km resolutions in the representation of precipitation at sub-daily timescales, and the atmospheric conditions leading to convection. Our results show that the highest resolution of RCM simulations significantly improves the representation of both hourly intensity distribution and diurnal cycle of precipitation. In addition, at convection permitting scale the atmospheric fields related to convective precipitation show a better agreement with each other. The results imply that higher spatial resolution partially improves the representation of the precipitation field, which must be the way forward for regional climate modelling.

  • 124.
    Arheimer, Berit
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Lindström, Göran
    SMHI, Forskningsavdelningen, Hydrologi.
    Climate impact on floods: changes in high flows in Sweden in the past and the future (1911-2100)2015Ingår i: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 19, nr 2, s. 771-784Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    There is an ongoing discussion whether floods occur more frequently today than in the past, and whether they will increase in number and magnitude in the future. To explore this issue in Sweden, we merged observed time series for the past century from 69 gauging sites throughout the country (450 000 km(2)) with high-resolution dynamic model projections of the upcoming century. The results show that the changes in annual maximum daily flows in Sweden oscillate between dry and wet periods but exhibit no significant trend over the past 100 years. Temperature was found to be the strongest climate driver of changes in river high flows, which are related primarily to snowmelt in Sweden. Annual daily high flows may decrease by on average -1% per decade in the future, mainly due to lower peaks from snowmelt in the spring (-2% per decade) as a result of higher temperatures and a shorter snow season. In contrast, autumn flows may increase by + 3% per decade due to more intense rainfall. This indicates a shift in floodgenerating processes in the future, with greater influence of rain-fed floods. Changes in climate may have a more significant impact on some specific rivers than on the average for the whole country. Our results suggest that the temporal pattern in future daily high flow in some catchments will shift in time, with spring floods in the northern-central part of Sweden occurring about 1 month earlier than today. High flows in the southern part of the country may become more frequent. Moreover, the current boundary between snow-driven floods in northern-central Sweden and rain-driven floods in the south may move toward higher latitudes due to less snow accumulation in the south and at low altitudes. The findings also indicate a tendency in observations toward the modeled projections for timing of daily high flows over the last 25 years. Uncertainties related to both the observed data and the complex model chain of climate impact assessments in hydrology are discussed.

  • 125. Aich, Valentin
    et al.
    Liersch, Stefan
    Vetter, Tobias
    Andersson, Jafet
    SMHI, Forskningsavdelningen, Hydrologi.
    Mueller, Eva N.
    Hattermann, Fred F.
    Climate or Land Use?-Attribution of Changes in River Flooding in the Sahel Zone2015Ingår i: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 7, nr 6, s. 2796-2820Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study intends to contribute to the ongoing discussion on whether land use and land cover changes (LULC) or climate trends have the major influence on the observed increase of flood magnitudes in the Sahel. A simulation-based approach is used for attributing the observed trends to the postulated drivers. For this purpose, the ecohydrological model SWIM (Soil and Water Integrated Model) with a new, dynamic LULC module was set up for the Sahelian part of the Niger River until Niamey, including the main tributaries Sirba and Goroul. The model was driven with observed, reanalyzed climate and LULC data for the years 1950-2009. In order to quantify the shares of influence, one simulation was carried out with constant land cover as of 1950, and one including LULC. As quantitative measure, the gradients of the simulated trends were compared to the observed trend. The modeling studies showed that for the Sirba River only the simulation which included LULC was able to reproduce the observed trend. The simulation without LULC showed a positive trend for flood magnitudes, but underestimated the trend significantly. For the Goroul River and the local flood of the Niger River at Niamey, the simulations were only partly able to reproduce the observed trend. In conclusion, the new LULC module enabled some first quantitative insights into the relative influence of LULC and climatic changes. For the Sirba catchment, the results imply that LULC and climatic changes contribute in roughly equal shares to the observed increase in flooding. For the other parts of the subcatchment, the results are less clear but show, that climatic changes and LULC are drivers for the flood increase; however their shares cannot be quantified. Based on these modeling results, we argue for a two-pillar adaptation strategy to reduce current and future flood risk: Flood mitigation for reducing LULC-induced flood increase, and flood adaptation for a general reduction of flood vulnerability.

  • 126. van Vliet, Michelle T. H.
    et al.
    Donnelly, Chantal
    SMHI, Forskningsavdelningen, Hydrologi.
    Strombäck, Lena
    SMHI, Forskningsavdelningen, Hydrologi.
    Capell, Réne
    SMHI, Forskningsavdelningen, Hydrologi.
    Ludwig, Fulco
    European scale climate information services for water use sectors2015Ingår i: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 528, s. 503-513Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study demonstrates a climate information service for pan-European water use sectors that are vulnerable to climate change induced hydrological changes, including risk and safety (disaster preparedness), agriculture, energy (hydropower and cooling water use for thermoelectric power) and environment (water quality). To study the climate change impacts we used two different hydrological models forced with an ensemble of bias-corrected general circulation model (GCM) output for both the lowest (2.6) and highest (8.5) representative concentration pathways (RCP). Selected indicators of water related vulnerability for each sector were then calculated from the hydrological model results. Our results show a distinct north-south divide in terms of climate change impacts; in the south the water availability will reduce while in the north water availability will increase. Across different climate models precipitation and streamflow increase in northern Europe and decrease in southern Europe, but the latitude at which this change occurs varies depending on the GCM. Hydrological extremes are increasing over large parts of Europe. The agricultural sector will be affected by reduced water availability (in the south) and increased drought. Both streamflow and soil moistures droughts are projected to increase in most parts of Europe except in northern Scandinavia and the Alps. The energy sector will be affected by lower hydropower potential in most European countries and reduced cooling water availability due to higher water temperatures and reduced summer river flows. Our results show that in particular in the Mediterranean the pressures are high because of increasing drought which will have large impacts on both the agriculture and energy sectors. In France and Italy this is combined with increased flood hazards. Our results show important impacts of climate change on European water use sectors indicating a clear need for adaptation. (C) 2015 Published by Elsevier B.V.

  • 127.
    Arheimer, Berit
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Nilsson, Johanna
    Lindström, Göran
    SMHI, Forskningsavdelningen, Hydrologi.
    Experimenting with Coupled Hydro-Ecological Models to Explore Measure Plans and Water Quality Goals in a Semi-Enclosed Swedish Bay2015Ingår i: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 7, nr 7, s. 3906-3924Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Measure plans are currently being developed for the Water Framework Directive (WFD) by European water authorities. In Sweden, such plans include measures for good ecological status in the coastal ecosystem. However, the effect of suggested measures is not yet known. We therefore experimented with different nutrient reduction measures on land and in the sea, using a model system of two coupled dynamic models for a semi-enclosed bay and its catchment. The science question was whether it is worthwhile to implement measures in the local catchment area to reach local environmental goals, or if the status of the Bay is more governed by the water exchange with the Sea. The results indicate that by combining several measures in the catchment, the nutrient load can be reduced by 15%-20%. To reach the same effect on nutrient concentrations in the Bay, the concentrations of the sea must be reduced by 80%. Hence, in this case, local measures have a stronger impact on coastal water quality. The experiment also show that the present targets for good ecological status set up by the Swedish water authorities may be unrealistic for this Bay. Finally, we discuss when and how to use hydro-ecological models for societal needs.

  • 128. Wilk, Julie
    et al.
    Hjerpe, Mattias
    Yang, Wei
    SMHI, Forskningsavdelningen, Hydrologi.
    Fan, Hua
    Farm-scale adaptation under extreme climate and rapid economic transition2015Ingår i: Environment, Development and Sustainability, ISSN 1387-585X, E-ISSN 1573-2975, Vol. 17, nr 3, s. 393-407Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper aims to analyse what shapes farmers' vulnerability and adaptation strategies in the context of rapid change. Xinjiang is semi-arid, with extremes of temperature, growing seasons and winds. Favourable socioeconomic conditions have boosted the wellbeing of farmers in the past decades. Interviews with forty-seven farmers led to the categorization of five groups according to the predominant type of farming activity: animal farmers, government farmers (leasing land from the Xinjiang Production and Construction Group), crop farmers, agri-tourism operators and entrepreneurs. High government support has aided farmers to deal with climate challenges, through advanced technology, subsidies and loans. Farmers, however, greatly contribute to their own high adaptive capacity through inventiveness, flexibility and a high knowledge base. Although the future climate will entail hotter temperatures, farmers can be seen as generally well equipped to deal with these challenges because of the high adaptive capacity they currently have and utilize. Those that are most vulnerable are those that have difficulty to access credit e.g. animal farmers and those that do not want to change their agricultural systems e.g. from pastoral lifestyles to include tourism-based operations.

  • 129. Thirel, G.
    et al.
    Andreassian, V.
    Perrin, C.
    Audouy, J. -N
    Berthet, L.
    Edwards, P.
    Folton, N.
    Furusho, C.
    Kuentz, A.
    Lerat, J.
    Lindström, Göran
    SMHI, Forskningsavdelningen, Hydrologi.
    Martin, E.
    Mathevet, T.
    Merz, R.
    Parajka, J.
    Ruelland, D.
    Vaze, J.
    Hydrology under change: an evaluation protocol to investigate how hydrological models deal with changing catchments2015Ingår i: Hydrological Sciences Journal, ISSN 0262-6667, E-ISSN 2150-3435, Vol. 60, nr 7-8, s. 1184-1199Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Testing hydrological models under changing conditions is essential to evaluate their ability to cope with changing catchments and their suitability for impact studies. With this perspective in mind, a workshop dedicated to this issue was held at the 2013 General Assembly of the International Association of Hydrological Sciences (IAHS) in Goteborg, Sweden, in July 2013, during which the results of a common testing experiment were presented. Prior to the workshop, the participants had been invited to test their own models on a common set of basins showing varying conditions specifically set up for the workshop. All these basins experienced changes, either in physical characteristics (e.g. changes in land cover) or climate conditions (e.g. gradual temperature increase). This article presents the motivations and organization of this experimentthat isthe testing (calibration and evaluation) protocol and the common framework of statistical procedures and graphical tools used to assess the model performances. The basins datasets are also briefly introduced (a detailed description is provided in the associated Supplementary material).

  • 130.
    Olsson, Jonas
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Berg, Peter
    SMHI, Forskningsavdelningen, Hydrologi.
    Kawamura, Akira
    Impact of RCM Spatial Resolution on the Reproduction of Local, Subdaily Precipitation2015Ingår i: Journal of Hydrometeorology, ISSN 1525-755X, E-ISSN 1525-7541, Vol. 16, nr 2, s. 534-547Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Many hydrological hazards are closely connected to local precipitation (extremes), especially in small and urban catchments. The use of regional climate model (RCM) data for small-scale hydrological climate change impact assessment has long been nearly unfeasible because of the low spatial resolution. The RCM resolution is, however, rapidly increasing, approaching the size of small catchments and thus potentially increasing the applicability of RCM data for this purpose. The objective of this study is to explore to what degree subhourly temporal precipitation statistics in an RCM converge to observed point statistics when gradually increasing the resolution from 50 to 6 km. This study uses precipitation simulated by RCA3 at seven locations in southern Sweden during 1995-2008. A positive impact of higher resolution was most clearly manifested in 10-yr intensity-duration-frequency (IDF) curves. At 50 km the intensities are underestimated by 50%-90%, but at 6 km they are nearly unbiased, when averaged over all locations and durations. Thus, at 6 km, RCA3 apparently generates low-frequency subdaily extremes that resemble the values found in point observations. Also, the reproduction of short-term variability and less extreme maxima were overall improved with increasing resolution. For monthly totals, a slightly increased overestimation with increasing resolution was found. The bias in terms of wet fraction and wet spell characteristics was overall not strongly dependent on resolution. These metrics are, however, influenced by the cutoff threshold used to separate between wet and dry time steps as well as the wet spell definition.

  • 131.
    Bergström, Sten
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Lindström, Göran
    SMHI, Samhälle och säkerhet.
    Interpretation of runoff processes in hydrological modelling experience from the HBV approach2015Ingår i: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 29, nr 16, s. 3535-3545Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The process of development and application of the Hydrologiska Byrans Vattenbalansavdelning hydrological model over a time period of more than 40years is reviewed and discussed. Emphasis is on the early modelling strategy and physical considerations based on contemporary research on runoff formation processes in the drainage basin. This includes areal considerations on the catchment scale, soil moisture and evapotranspiration and storages and discharge as represented by the response function of the model. The introduction of the concept of dynamic recharge and discharge areas is also addressed as well as the modelling of snow accumulation and melt. Some operational international experiences are also addressed. Copyright (c) 2015 John Wiley & Sons, Ltd.

  • 132.
    Andersson, Jafet
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Pechlivanidis, Ilias
    SMHI, Forskningsavdelningen, Hydrologi.
    Gustafsson, David
    SMHI, Forskningsavdelningen, Hydrologi.
    Donnelly, Chantal
    SMHI, Forskningsavdelningen, Hydrologi.
    Arheimer, Berit
    SMHI, Forskningsavdelningen, Hydrologi.
    Key factors for improving large-scale hydrological model performance2015Ingår i: European Water, ISSN 1792-085X, Vol. 49, s. 77-88Artikel i tidskrift (Refereegranskat)
  • 133.
    Pechlivanidis, Ilias
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Arheimer, Berit
    SMHI, Forskningsavdelningen, Hydrologi.
    Large-scale hydrological modelling by using modified PUB recommendations: the India-HYPE case2015Ingår i: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 19, nr 11, s. 4559-4579Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The scientific initiative Prediction in Ungauged Basins (PUB) (2003-2012 by the IAHS) put considerable effort into improving the reliability of hydrological models to predict flow response in ungauged rivers. PUB's collective experience advanced hydrologic science and defined guidelines to make predictions in catchments without observed runoff data. At present, there is a raised interest in applying catchment models to large domains and large data samples in a multi-basin manner, to explore emerging spatial patterns or learn from comparative hydrology. However, such modelling involves additional sources of uncertainties caused by the inconsistency between input data sets, i.e. particularly regional and global databases. This may lead to inaccurate model parameterisation and erroneous process understanding. In order to bridge the gap between the best practices for flow predictions in single catchments and multi-basins at the large scale, we present a further developed and slightly modified version of the recommended best practices for PUB by Takeuchi et al. (2013). By using examples from a recent HYPE (Hydrological Predictions for the Environment) hydrological model set-up across 6000 subbasins for the Indian subcontinent, named India-HYPE v1.0, we explore the PUB recommendations, identify challenges and recommend ways to overcome them. We describe the work process related to (a) errors and inconsistencies in global databases, unknown human impacts, and poor data quality; (b) robust approaches to identify model parameters using a stepwise calibration approach, remote sensing data, expert knowledge, and catchment similarities; and (c) evaluation based on flow signatures and performance metrics, using both multiple criteria and multiple variables, and independent gauges for "blind tests". The results show that despite the strong physiographical gradient over the subcontinent, a single model can describe the spatial variability in dominant hydrological processes at the catchment scale. In addition, spatial model deficiencies are used to identify potential improvements of the model concept. Eventually, through simultaneous calibration using numerous gauges, the median Kling-Gupta efficiency for river flow increased from 0.14 to 0.64. We finally demonstrate the potential of multi-basin modelling for comparative hydrology using PUB, by grouping the 6000 subbasins based on similarities in flow signatures to gain insights into the spatial patterns of flow generating processes at the large scale.

  • 134.
    Berg, Peter
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Bosshard, Thomas
    SMHI, Forskningsavdelningen, Hydrologi.
    Yang, Wei
    SMHI, Forskningsavdelningen, Hydrologi.
    Model Consistent Pseudo-Observations of Precipitation and Their Use for Bias Correcting Regional Climate Models2015Ingår i: CLIMATE, ISSN 2225-1154, Vol. 3, nr 1, s. 118-132Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lack of suitable observational data makes bias correction of high space and time resolution regional climate models (RCM) problematic. We present a method to construct pseudo-observational precipitation data by merging a large scale constrained RCM reanalysis downscaling simulation with coarse time and space resolution observations. The large scale constraint synchronizes the inner domain solution to the driving reanalysis model, such that the simulated weather is similar to observations on a monthly time scale. Monthly biases for each single month are corrected to the corresponding month of the observational data, and applied to the finer temporal resolution of the RCM. A low-pass filter is applied to the correction factors to retain the small spatial scale information of the RCM. The method is applied to a 12.5 km RCM simulation and proven successful in producing a reliable pseudo-observational data set. Furthermore, the constructed data set is applied as reference in a quantile mapping bias correction, and is proven skillful in retaining small scale information of the RCM, while still correcting the large scale spatial bias. The proposed method allows bias correction of high resolution model simulations without changing the fine scale spatial features, i.e., retaining the very information required by many impact models.

  • 135.
    Yang, Wei
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Gardelin, Marie
    SMHI, Affärsverksamhet.
    Olsson, Jonas
    SMHI, Forskningsavdelningen, Hydrologi.
    Bosshard, Thomas
    SMHI, Forskningsavdelningen, Hydrologi.
    Multi-variable bias correction: application of forest fire risk in present and future climate in Sweden2015Ingår i: Natural hazards and earth system sciences, ISSN 1561-8633, E-ISSN 1684-9981, Vol. 15, nr 9, s. 2037-2057Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As the risk of a forest fire is largely influenced by weather, evaluating its tendency under a changing climate becomes important for management and decision making. Currently, biases in climate models make it difficult to realistically estimate the future climate and consequent impact on fire risk. A distribution-based scaling (DBS) approach was developed as a post-processing tool that intends to correct systematic biases in climate modelling outputs. In this study, we used two projections, one driven by historical reanalysis (ERA40) and one from a global climate model (ECHAM5) for future projection, both having been dynamically down-scaled by a regional climate model (RCA3). The effects of the post-processing tool on relative humidity and wind speed were studied in addition to the primary variables precipitation and temperature. Finally, the Canadian Fire Weather Index system was used to evaluate the influence of changing meteorological conditions on the moisture content in fuel layers and the fire-spread risk. The forest fire risk results using DBS are proven to better reflect risk using observations than that using raw climate outputs. For future periods, southern Sweden is likely to have a higher fire risk than today, whereas northern Sweden will have a lower risk of forest fire.

  • 136. Hytteborn, Julia K.
    et al.
    Temnerud, Johan
    SMHI, Forskningsavdelningen, Hydrologi.
    Alexander, Richard B.
    Boyer, Elizabeth W.
    Futter, Martyn N.
    Froberg, Mats
    Dahne, Joel
    SMHI, Affärsverksamhet.
    Bishop, Kevin H.
    Patterns and predictability in the intra-annual organic carbon variability across the boreal and hemiboreal landscape2015Ingår i: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 520, s. 260-269Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Factors affecting total organic carbon (TOC) concentrations in 215 watercourses across Sweden were investigated using parameter parsimonious regression approaches to explain spatial and temporal variabilities of the TOC water quality responses. We systematically quantified the effects of discharge, seasonality, and long-term trend as factors controlling intra-annual (among year) and inter-annual (within year) variabilities of TOC by evaluating the spatial variability in model coefficients and catchment characteristics (e.g. land cover, retention time, soil type). Catchment area (0.18-47,000 km(2)) and land cover types (forests, agriculture and alpine terrain) are typical for the boreal and hemiboreal zones across Fennoscandia. Watercourses had at least 6 years of monthly water quality observations between 1990 and 2010. Statistically significant models (p < 0.05) describing variation of TOC in streamflow were identified in 209 of 215 watercourses with a mean Nash-Sutcliffe efficiency index of 0.44. Increasing long-term trends were observed in 149 (70%) of the watercourses, and intra-annual variation in TOC far exceeded inter-annual variation. The average influences of the discharge and seasonality terms on intra-annual variations in daily TOC concentration were 1.4 and 1.3 mg l(-1) (13 and 12% of the mean annual TOC), respectively. The average increase in TOC was 0.17 mg l(-1) year(-1) (1.6% year(-1)). Multivariate regression with over 90 different catchment characteristics explained 21% of the spatial variation in the linear trend coefficient, less than 20% of the variation in the discharge coefficient and 73% of the spatial variation in mean TOC. Specific discharge, water residence time, the variance of daily precipitation, and lake area, explained 45% of the spatial variation in the amplitude of the TOC seasonality. Because the main drivers of temporal variability in TOC are seasonality and discharge, first-order estimates of the influences of climatic variability and change on TOC concentration should be predictable if the studied catchments continue to respond similarly. (C) 2015 Elsevier B.V. All rights reserved.

  • 137.
    Olsson, Jonas
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Simonsson, Lennart
    SMHI, Forskningsavdelningen, Hydrologi.
    Ridal, Martin
    SMHI, Forskningsavdelningen, Meteorologi.
    Rainfall nowcasting: predictability of short-term extremes in Sweden2015Ingår i: Urban Water Journal, ISSN 1573-062X, Vol. 12, nr 1, s. 3-13Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Our current knowledge of the character of rainfall events in Sweden associated with extreme short-term accumulations and their predictability by forecasting, is very limited. In this study, observations from automatic stations and weather radars in Sweden were analysed to identify and characterise extreme short-term events. Often shorter-duration (1-6 h) extreme events were associated with small-scale structures, dominated by single cells, and longer-duration (12-24 h) events with less variable, larger-scale fields. For lead time 3 h, similar to 20% of the events were forecasted at the correct place with an error of <25% by the operational Swedish nowcasting system. If allowing for a 25 km displacement of the forecasted events, the hit rate increased by 10-15 percentage points. Some predictability was found for lead time 8 h but not for 24 h. The results suggest a potential added gain of increasing the temporal resolution of the Swedish flood forecasting system to sub-daily steps.

  • 138. Kayhko, Jukka
    et al.
    Apsite, Elga
    Bolek, Anna
    Filatov, Nikolai
    Kondratyev, Sergey
    Korhonen, Johanna
    Kriauciuniene, Jurate
    Lindström, Göran
    SMHI, Forskningsavdelningen, Hydrologi.
    Nazarova, Larisa
    Pyrh, Anna
    Sztobryn, Marzenna
    Recent Change-River Run-off and Ice Cover2015Kapitel i bok, del av antologi (Övrigt vetenskapligt)
    Abstract [en]

    This chapter compiles and assesses information on run-off and discharge from rivers within the Baltic Sea drainage basin. Some information is also available on ice duration on inland waterways. Although decadal and regional variability is large, no significant long-term change has been detected in total river run-off to the Baltic Sea over the past 500 years. A change in the timing of the spring flood has been observed due to changes in the timing of snowmelt. Change in temperature seems to explain change in run-off better than does precipitation. Later start dates for ice formation on waterways, and earlier ice break-up dates have resulted in shorter periods of ice cover.

  • 139.
    Andersson, Lotta
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Persson, Gunn
    SMHI, Affärsverksamhet.
    Bergström, Sten
    SMHI, Samhälle och säkerhet.
    Ohlsson, Alexandra
    SMHI, Affärsverksamhet.
    Risker, konsekvenser och sårbarhet för samhället av förändrat klimat – en kunskapsöversikt: Flertalet av de i rapporten refererade myndigheterna och organisationerna har varit aktiva i framtagandet av texterna: Materialet har sammanställts av:2015Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Regeringen gav år 2014 SMHI i uppdrag att utarbeta underlag till Kontrollstation2015 för anpassning till ett förändrat klimat. Som en del av uppdraget ingick att göra en uppdaterad sammanställning av kunskapen om nuvarande och framtida risker och konsekvenser, främst med utgångspunkt från Klimat- och sårbarhetsutredningens slutbetänkande (SOU 2007:60). I föreliggande rapport beskrivs kunskapsläget kring det svenska samhällets sårbarhet för ett förändrat klimat. Klimatförändringarna påverkar hela samhället. Generellt kan sägas att medvetenheten om klimatförändringarnas påverkan har ökat, men det saknas en del kunskap och verktyg, främst på den lokala nivån. Översvämningsriskerna kring sjöar och längs vattendrag ökar, vilket kan påverka bebyggelse och infrastruktur. Risken för ras och skred tros också öka, främst i landets västra och sydvästra delar samt områden längs östra kusten. Erosion längs vattendrag, sjöar och kuster kan komma att öka i delar av landet. Vattentillgång och -kvalitet kommer att påverkas av förändrade nederbördsmönster, ökad spridning av föroreningar samt ökade mikrobiologiskarisker. Energisystemet kommer att utsättas för större påfrestningar, särskilt av extrema väderhändelser. Kunskapen har ökat kring klimatförändringarnas effekter på energisystemet, men det kvarstår kunskapsluckor relaterade till extremväder och anpassningsåtgärder. Kunskap och medvetenhet om klimatförändringarnas påverkan på kommunikationerna i samhället har ökat, men det finns fortfarande behov av mer utredning och verktyg. Förutsättningarna för jordbruket förbättras i huvudsak, med möjlighet till ökade skördar och nya grödor. Samtidigt kommer fler skadegörare och ogräs in. Nya behov av bevattning kan uppstå och markavvattningen kan behöva en översyn. Eventuellt minskat utbud av livsmedel på världsmarknaden, kan innebära ökad efterfrågan på svenska livsmedel. Samtidigt går Sverige idag mot ökat importberoende. Även djurhållningen står inför stora utmaningar. Å ena sidan kan djuren gå ute under en längre del av året och möjligheterna att vara självförsörjande med foder ökar. Men det varmare klimatet medför också risk för att nya djursjukdomar uppträder. Konsekvenserna för den svenska skogen och skogsbruket kommer att bli betydande. Ökad tillväxt ger större virkesproduktion, men ökad frekvens och omfattning av skador från främst insekter, svampar och storm samt blötare skogsmark kan föra med sig stora kostnader. Stora regionala skillnader i utbudet av kommersiellt virke kan påverka svensk skogsindustri. Förändrade förutsättningar är också att vänta för fiskbestånden. Nya fiskarter i svenska vatten kan föra med sig nya smittor och konkurrera ut befintliga arter i känsliga ekosystem. Renskötseln i Sverige kommer att allvarligt påverkas av klimatförändringarna och effekterna utgör stora utmaningar. Klimatförändringarna ger både positiva och negativa effekter för turismen. Det finns hinder för anpassningskapaciteten, bland annat bristande organisering av besöksnäringen. Människors och djurs hälsa kan påverkas direkt av extrema väderhändelser. Ett varmare klimat ger även upphov till förändrade smittspridningsmönster och nya sjukdomar kan nå Sverige. Förändringar i luft, vatten och mark, orsakade av klimatförändringar, kan också påverka hälsotillståndet för djur och människor. På nationell nivå är kunskaperna om risker för bebyggelse tillräckliga för att rekommendera åtgärder, men det saknas lokala beslutsunderlag. För kulturarvet behöver kunskapen öka. Klimatförändringarna förväntas leda till förändringar för den biologiska mångfalden och ekosystemen. Det påverkar förmågan att nå flera av Sveriges miljömål och behöver ses i samband med andra miljöhot. Det finns bland annat behov av regionala kartläggningar av hur arter, ekosystem, naturtyper och biologisk mångfald kan påverkas. Risk- och säkerhetsperspektivet har växt fram under senare år, men präglas av utmaningar avseende metoder. Mycket få studier behandlar förhållanden i Sverige.

  • 140. Pechlivanidis, G. I.
    et al.
    Keramaris, E.
    Pechlivanidis, Ilias
    SMHI, Forskningsavdelningen, Hydrologi.
    Samaras, G. A.
    Shear stress estimation in the linear zone over impermeable and permeable beds in open channels2015Ingår i: Desalination and Water Treatment, ISSN 1944-3994, E-ISSN 1944-3986, Vol. 54, nr 8, s. 2181-2189Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper investigates the shear stresses in the linear zone of open channel flows with permeable and impermeable bed. The permeable bed is simulated using a flexible vegetation of 2 cm thickness. Laboratory experiments were used for the calculation of the turbulent velocity profiles. The measurements were obtained using a two-dimensional (2D) particle image velocimetry (PIV). This optical method of fluid visualization is used to obtain instantaneous velocity measurements related properties in the fluids. The PIV method assumes that the particles of a fluid faithfully follow the flow dynamics; hence the motion of these seeding particles is used to calculate the dynamic characteristics of the flow. The measurements were conducted at a 12 x 10 cm(2) region located 4 m away from the channel's entrance, where the flow is considered fully developed. The uniformity of the flow was checked measuring the flow depth at two cross-sections (2 m distance between the two regions). The total discharge was estimated using a calibrated venture apparatus. Measurements of velocity were taken for the horizontal channel slope. Results showed that the type of bed can significantly influence the shear stress definition in the linear zone.

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