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  • 1. Akselsson, Cecilia
    et al.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Belyazid, Salim
    Capell, Réne
    SMHI, Research Department, Hydrology.
    Can increased weathering rates due to future warming compensate for base cation losses following whole-tree harvesting in spruce forests?2016In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 128, no 1-2, p. 89-105Article in journal (Refereed)
  • 2. Amaguchi, H.
    et al.
    Kawamura, A.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Takasaki, T.
    Development and testing of a distributed urban storm runoff event model with a vector-based catchment delineation2012In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 420, p. 205-215Article in journal (Refereed)
    Abstract [en]

    The recent advances in GIS technology as well as data availability open up new possibilities concerning urban storm runoff modeling. In this paper, a vector-based distributed storm event runoff model - the Tokyo Storm Runoff (TSR) model - is developed and tested for urban runoff analysis using two historical storm events. The set-up of this model is based on urban landscape GIS delineation that faithfully describes the complicated urban land use features in detail. The flow between single spatial elements is based on established hydraulic and hydrological models with equations that describe all aspects of storm runoff generation in an urban environment. The model was set up and evaluated for the small urban lower Ekota catchment in Tokyo Metropolis, Japan. No calibration or tuning was performed, but the general model formulation was used with standard parameter values obtained from the literature. The runoff response to two storm events were simulated; one minor event resulting only in a small-scale flood wave and one major event which inundated parts of the catchment. For both events, the simulated water levels closely reproduced the observed ones. For the major event, also the reported inundation area was well described by the model. It was also demonstrated how the model can be used to evaluate the flow conditions in specific components of the urban hydrological system, which facilitates e.g. evaluation of flood-preventive measures. (C) 2011 Elsevier B.V. All rights reserved.

  • 3.
    Andersson, Lotta
    et al.
    SMHI, Core Services.
    Rosberg, Jörgen
    SMHI, Research Department, Hydrology.
    Pers, Charlotta
    SMHI, Research Department, Hydrology.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Estimating catchment nutrient flow with the HBV-NP model: Sensitivity to input data2005In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 34, no 7, p. 521-532Article in journal (Refereed)
    Abstract [en]

    The dynamic catchment model HBV-N has been further developed by adding routines for phosphorus transport and is now called the HBV-NP model. The model was shown to satisfactorily simulate nutrient dynamics in the Ronnea catchment (1 900 km(2)). Its sensitivity to input data was tested, and results demonstrated the increased sensitivity to the selection of input data on a subcatchment scale when compared with the catchment scale. Selection of soil and land use databases was found to be critical in some subcatchments but did not have a significant impact on a catchment scale. Although acceptable on a catchment scale, using templates and generalization, with regards to emissions from point sources and rural households, significantly decreased model performance in certain subcatchments when compared with using more detailed local information. A division into 64 subcatchments resulted in similar model performance at the catchment outlet when compared with a lumped approach. Adjusting the imported matrixes of the regional leaching of nitrogen, from agricultural land, against mean subcatchment water percolation did not have a significant impact on the model performance.

  • 4.
    Arheimer, Berit
    et al.
    SMHI, Research Department, Hydrology.
    Andersson, Lotta
    SMHI, Core Services.
    Larsson, M
    Lindström, Göran
    SMHI, Research Department, Hydrology.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Pers, Charlotta
    SMHI, Research Department, Hydrology.
    Modelling diffuse nutrient flow in eutrophication control scenarios2004In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 49, no 3, p. 37-45Article in journal (Refereed)
    Abstract [en]

    The Swedish Water Management Research Programme (VASTRA) focuses on the development and demonstration of tools for more efficient eutrophication control when implementing the EU water framework directive in Sweden. During the first half of the programme, models for nitrogen flow were developed, and at present, similar models for phosphorus are under construction (e.g. HBV-P). The programme is interdisciplinary, and scientists are collaborating in actor-games and focus group evaluations including scenario analysis. The scenarios modelled in VASTRA phase 1, show that (i) changed agricultural practices can be the most effective and-least expensive way to reduce nitrogen transport from land to, the sea; (ii) constructed agricultural wetlands may only have small impact on riverine nitrogen transport in some regions, due to natural hydrometeorological dynamics; (iii) removing planktivorous fish may be an efficient way of reducing the algal concentrations in lakes without the undesired side-effect of increased nutrient load to the down-stream river system. In VASTRA phase 11, one of the highlights will be interdisciplinary scenario-modelling of different measure strategies in a pilot catchment of southern Sweden (Ronne a).

  • 5.
    Arheimer, Berit
    et al.
    SMHI, Research Department, Hydrology.
    Lindström, Göran
    SMHI, Research Department, Hydrology.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    A systematic review of sensitivities in the Swedish flood-forecasting system2011In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 100, no 2-3, p. 275-284Article, review/survey (Refereed)
    Abstract [en]

    Since the early 1970s operational flood forecasts in Sweden have been based on the hydrological HBV model. However, the model is only one component in a chain of processes for production of hydrological forecasts. During the last 35 years there has been considerable work on improving different parts of the forecast procedure and results from specific studies have been reported frequently. Yet, the results have not been compared in any overall assessment of potential for improvements. Therefore we formulated and applied a method for translating results from different studies to a common criterion of error reduction. The aim was to quantify potential improvements in a systems perspective and to identify in which part of the production chain efforts would result in significantly better forecasts. The most sensitive (> 20% error reduction) components were identified for three different operational-forecast types. From the analyses of historical efforts to minimise the errors in the Swedish flood-forecasting system, it was concluded that 1) general runoff simulations and predictions could be significantly improved by model structure and calibration, model equations (e.g. evapotranspiration expression), and new precipitation input using radar data as a complement to station gauges; 2) annual spring-flood forecasts could be significantly improved by better seasonal meteorological forecast, fresh re-calibration of the hydrological model based on long time-series, and data assimilation of snow-pack measurements using georadar or gamma-ray technique; 3) short-term (2 days) forecasts could be significantly improved by up-dating using an auto-regressive method for discharge, and by ensembles of meteorological forecasts using the median at occasions when the deterministic forecast is out of the ensemble range. The study emphasises the importance of continuously evaluating the entire production chain to search for potential improvements of hydrological forecasts in the operational environment. (C) 2010 Elsevier B.V. All rights reserved.

  • 6. Arnbjerg-Nielsen, K.
    et al.
    Willems, P.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Beecham, S.
    Pathirana, A.
    Gregersen, I. Bulow
    Madsen, H.
    Nguyen, V. -T-V
    Impacts of climate change on rainfall extremes and urban drainage systems: a review2013In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 68, no 1, p. 16-28Article, review/survey (Refereed)
    Abstract [en]

    A review is made of current methods for assessing future changes in urban rainfall extremes and their effects on urban drainage systems, due to anthropogenic-induced climate change. The review concludes that in spite of significant advances there are still many limitations in our understanding of how to describe precipitation patterns in a changing climate in order to design and operate urban drainage infrastructure. Climate change may well be the driver that ensures that changes in urban drainage paradigms are identified and suitable solutions implemented. Design and optimization of urban drainage infrastructure considering climate change impacts and co-optimizing these with other objectives will become ever more important to keep our cities habitable into the future.

  • 7. Bengtsson, L.
    et al.
    Grahn, L
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Hydrological function of a thin extensive green roof in southern Sweden2005In: Nordic Hydrology, ISSN 0029-1277, E-ISSN 1996-9694, Vol. 36, no 3, p. 259-268Article in journal (Refereed)
    Abstract [en]

    The runoff from and the water balance of a thin extensive green roof with sedum-moss have been studied. The soil cover is about 3 cm underlain by a thin drainage layer. The water balance is determined on a monthly basis. The runoff from the green roof is much reduced compared to runoff from hard roofs because of evapotranspiration. The annual runoff is rather close to that of natural river basins. Although most rainy days there is no or little runoff from the roof, the highest observed daily runoff values are close to the daily rainfall. Runoff is initiated when the soil is at field capacity, which for the studied roof corresponds to 9 mm storage. After that, on a not very short time basis, the runoff equals the precipitation. The reduction of the daily runoff can be described in a simple way knowing the daily precipitation, potential evaporation and storage capacity of the green roof.

  • 8.
    Berg, Peter
    et al.
    SMHI, Research Department, Hydrology.
    Norin, Lars
    SMHI, Research Department, Atmospheric remote sensing.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Creation of a high resolution precipitation data set by merging gridded gauge data and radar observations for Sweden2016In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 541, p. 6-13Article in journal (Refereed)
  • 9. Bruen, M.
    et al.
    Krahe, P.
    Zappa, M.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Vehvilainen, B.
    Kok, K.
    Daamen, K.
    Visualizing flood forecasting uncertainty: some current European EPS platforms-COST731 working group 32010In: Atmospheric Science Letters, ISSN 1530-261X, E-ISSN 1530-261X, Vol. 11, no 2, p. 92-99Article in journal (Refereed)
    Abstract [en]

    Cooperation in Science and Technology (COST) funding allows European scientists to establish international links, communicate their work to colleagues, and promote international research cooperation. COST731 was established to study the propagation of uncertainty from hydrometeorological observations through meteorological and hydrological models to the final flood forecast. Our focus is on how information about uncertainty is presented to the end user and how it is used. COST731 has assembled a number of demonstrations/case studies that illustrate a variety of practical approaches and these are presented here. While there is yet no consensus on how such information is presented, many end users do find it useful. Copyright (C) 2010 Royal Meteorological Society

  • 10.
    Eklund, Anna
    et al.
    SMHI, Core Services.
    Axén Mårtensson, Jenny
    SMHI, Core Services.
    Bergström, Sten
    SMHI, Research Department, Hydrology.
    Björck, Emil
    SMHI, Professional Services.
    Dahné, Joel
    SMHI, Professional Services.
    Lindström, Lena
    SMHI, Core Services.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Simonsson, Lennart
    SMHI, Research Department, Hydrology.
    Sjökvist, Elin
    SMHI, Professional Services.
    Sveriges framtida klimat: Underlag till Dricksvattenutredningen2015Report (Other academic)
    Abstract [en]

    The latest results from climate research have been used to produce detailed analyses of Sweden’s future climate. The results build on the climate scenarios that have been used by the UN’s climate panel in its Fifth Assessment Report (AR5). Two scenarios have been used in this analysis: RCP4.5, which significantly limits future emissions, and RCP8.5, which is a more conservative “business as usual” scenario. Calculations of the future climate and water availability are based on new material and some new conditions compared to analyses previously presented by SMHI. The calculated changes in precipitation, temperature, water availability and flooding are broadly the same as earlier reports. The use of the RCP8.5 scenario, with its high future concentration of greenhouse gases, strengthens the effects compared to previous analyses. Since the results of the UNs climate panel (AR5) were presented as late as 2013, the material produced by SMHI has involved intensive development. The results have required new methodologies and will continue to be evaluated by SMHI. Analyses have been made for a number of parameters that are relevant to the supply of drinking water. The table below summarises the results. Parameter Change Airtemperature Increasing in the whole country, in particular in northern Sweden, mainly during winter. Average precipitation Increasing in the whole country, in particular inland Norrland, mainly during winter and spring. Extreme short-term precipitation Increasing in the whole country, mainly for short-term heavy showers. Water availability Increasing in the whole country except for eastern Götaland. The increase is greatest during the winter. Decreasing during summer, in particular in eastern Götaland. 100-year floods and 200-year floods Increasing in large areas of the country. Decreasing in inland Norrland and the northern coast as well as north west Svealand. Low river flows Becoming more common in Götaland and Svealand, particularly in eastern Götaland. Sea levels Raised sea levels, with the greatest net rise in southern Sweden. Temperature Climate calculations show an increase in the mean annual temperature during the current century, but with a large spread of the result. The largest increase is calculated for the north, which is in agreement with earlier results from both SMHI and IPCC. The difference between the two emission scenarios is small for the period 2021-2050 but increases towards the end of the century. The RCP4.5 scenario implies an increase of around 3 degrees on average by 2100, compared to the period 1961-1990. The increase is greater for RCP8.5, giving an average of around 6 degrees by 2100. Precipitation Average precipitation is calculated to increase for the whole country in the future. The greatest increase is expected for inland Norrland. The difference between the two emission scenarios is small for the period 2021-2050 but increases by the end of the century. An increase is expected during all seasons, but mostly for winter and spring. Extreme short-term precipitation is calculated to become more intensive in a future climate. This applies particularly to short torrential showers. Water availability and flow In the future, an increase in water availability is expected in large parts of the country, particularly in northern Sweden and along the West Coast. Southern Sweden can instead expect a reduction which is due to increased evaporation. For large parts of the country the spring floods are expected to be lower and the winter floods will increase. The change in water availability differs between the seasons. During summer a decreasing in water availability is expected in large parts of the country, in particular in eastern Götaland. Extreme floods are expected to occur less often in inland Norrland, the northern coastal areas and for north western Svealand. In the rest of the country, extreme floods are expected to be more common. New calculations show that a larger part of Sweden’s area could be susceptible to stronger extreme floods compared to earlier calculations. In the future, more days with low river flows are expected in Götaland and large parts of Svealand. The greatest change is expected in eastern Götaland. This is a result of increased evaporation due to the rise in temperature. Sea level The global sea level is expected to rise in the future. A calculated upper limit for the increase has been put at about 1 m by the year 2100 according to the latest evaluation from IPCC. The land rise counteracts the rise in sea level, in particular for northern Sweden. Precipitation Average precipitation is calculated to increase for the whole country in the future. The greatest increase is expected for inland Norrland. The difference between the two emission scenarios is small for the period 2021-2050 but increases by the end of the century. An increase is expected during all seasons, but mostly for winter and spring. Extreme short-term precipitation is calculated to become more intensive in a future climate. This applies particularly to short torrential showers. Water availability and flow In the future, an increase in water availability is expected in large parts of the country, particularly in northern Sweden and along the West Coast. Southern Sweden can instead expect a reduction which is due to increased evaporation. For large parts of the country the spring floods are expected to be lower and the winter floods will increase. The change in water availability differs between the seasons. During summer a decreasing in water availability is expected in large parts of the country, in particular in eastern Götaland. Extreme floods are expected to occur less often in inland Norrland, the northern coastal areas and for north western Svealand. In the rest of the country, extreme floods are expected to be more common. New calculations show that a larger part of Sweden’s area could be susceptible to stronger extreme floods compared to earlier calculations. In the future, more days with low river flows are expected in Götaland and large parts of Svealand. The greatest change is expected in eastern Götaland. This is a result of increased evaporation due to the rise in temperature. Sea level The global sea level is expected to rise in the future. A calculated upper limit for the increase has been put at about 1 m by the year 2100 according to the latest evaluation from IPCC. The land rise counteracts the rise in sea level, in particular for northern Sweden.

  • 11.
    Foster, Kean
    et al.
    SMHI, Research Department, Hydrology.
    Uvo, Cintia Bertacchi
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    The development and evaluation of a hydrological seasonal forecast system prototype for predicting spring flood volumes in Swedish rivers2018In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 22, no 5, p. 2953-2970Article in journal (Refereed)
  • 12.
    Graham, Phil
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Rosberg, Jörgen
    SMHI, Research Department, Hydrology.
    Hellström, Sara-Sofia
    SMHI, Research Department, Hydrology.
    Berndtsson, Ronny
    Simulating river flow to the Baltic Sea from climate simulations over the past millennium2009In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 14, no 1, p. 173-182Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to reconstruct river flow to the Baltic Sea using data from different periods during the past thousand years. A hydrological model coupled to simulations from climate models was used to estimate river flow. A "millennium" simulation of past climate from the ECHO-G coupled atmosphere-ocean global climate model provided climatological inputs. Results from this global model were downscaled with the RCA3 regional climate model over northern Europe. Temperature and precipitation from the downscaled simulation results were then used in the HBV hydrological model to simulate river flows to the Baltic Sea for the periods 1000-1199 and 1551-1929. These were compared with observations for the period 1921-2002. A general conclusion from this work is that although climate has varied during the past millennium, variability in annual river flow to the Baltic Sea does not appear more pronounced in recent years than during the previous millennium, or vice versa.

  • 13.
    Johansson, Barbro
    et al.
    SMHI, Professional Services.
    Lindström, Göran
    SMHI, Research Department, Hydrology.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Yacoub, Tahsin
    SMHI, Core Services.
    Haase, Günther
    SMHI, Research Department, Atmospheric remote sensing.
    Jacobsson, Karin
    SMHI, Professional Services.
    Sanner, Håkan
    SMHI, Core Services.
    Översvämningsprognoser i områden med ofullständiga data: Metodutveckling och utvärdering2007Report (Other academic)
    Abstract [sv]

    Rapporten redovisar slutresultat från projektet ”Översvämningsprognoser Utveckling av metoder för ett rikstäckande system för vattenförings- och vattenståndsprognoser”. Projektet har i huvudsak varit finansierat av Räddningsverket, numera MSB, (Myndigheten för Samhällsskydd och Beredskap), men har även utnyttjat resultat från näraliggande projekt finansierade av Elforsk, SMHI och EU.I ett rikstäckande system måste prognoser göras för vattendrag där det saknas detaljerad information om avrinningsområdets och älvfårans egenskaper. Modeller kan inte tillämpas och verifieras på samma sätt som i områden med god datatillgång och tillgång till tidsserier med observerad vattenföring. Eftersom beräkningarna inte kan verifieras mot observationer blir det extra viktigt med bra nederbördsinformation och att kunna ge ett mått på osäkerheten i prognosen. Projektet har dels arbetat med metodutveckling, dels med en omfattande utvärdering av data och beräkningsresultat. En pilotstudie gjordes för flödet sommaren 2004 i Lagan/Ljungby. Fokus har varit på följande områden:- Utveckling och utvärdering av en metodik för att utnyttja meteorologiska och hydrologiska sannolikhetsprognoser- Utvärdering och minimering av osäkerheten i hydrologiska (vattenföring) och hydrauliska (vattenstånd) prognosmodeller.- Utveckling och utvärdering av metoder för att utnyttja radarobservationer av nederbörd.Projektet har visat att det är möjligt att göra vattenståndsprognoser med rimlig noggrannhet, utgående från data som finns tillgängliga i ett rikstäckande system. Tillgång till bra nederbördsinformation för dagarna före prognosen är viktig, speciellt i sjörika system med ett långsamt förlopp. För att kunna göra sannolikhetsprognoser räcker det inte att ta hänsyn till osäkerheten i den meteorologiska prognosen genom att direkt utnyttja meteorologiska ensembleprognoser. Spridningen i de meteorologiska nederbördsprognoserna är inte tillräcklig och osäkerheten i den hydrologiska modellen måste beaktas.De projektresultat som inom det närmaste året kommer att utnyttjas i ett rikstäckande system är de som är relaterade till hydrologisk modellering och sannolikhetsprognoser. Arbetet med att utveckla metoder för att utnyttja radarinformation i operationell skattning av arealnederbörd fortgår. Fallstudier har visat att vattenståndsprognoser kan göras med modeller baserad på översiktlig information om topografi och tvärsektioner i vattendragen. Däremot är det tidsödande att sätta upp en hydraulisk modell för en godtycklig älvsträcka. Tills vidare är det realistiskt att anta att vattenståndsprognoser främst kommer att göras i vattendrag som ingått i den översiktliga översvämningskarteringen.

  • 14.
    Johnell, Anna
    et al.
    SMHI, Professional Services.
    Lindström, Göran
    SMHI, Research Department, Hydrology.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Deterministic evaluation of ensemble streamflow predictions in Sweden2007In: Nordic Hydrology, ISSN 0029-1277, E-ISSN 1996-9694, Vol. 38, no 4-5, p. 441-450Article in journal (Refereed)
    Abstract [en]

    A system for ensemble streamflow prediction, ESP, has been operational at SMHI since July 2004, based on 50 meteorological ensemble forecasts from ECMWF. Hydrological ensemble forecasts are produced daily for 51 basins in Sweden. All ensemble members, as well as statistics (minimum, 25% quartile, median, 75% quartile and maximum), are stored in a database. This paper presents an evaluation of the first 18 months of ESP median forecasts from this system, and in particular their performance in comparison with today's categorical forecast. The evaluation was made in terms of three statistical measures: bias B, root mean square error RMSE and absolute peak flow error PE. For ESP forecasts the bias ranged between -20% and 80% with a systematic overestimation for Sweden as a whole. A comparison between bias in input precipitation and ESP output, respectively, revealed only a weak relationship, but streamflow overestimation is likely related mainly to model properties. The results from the streamflow forecast comparison showed that the ESP median in deterministic terms performs overall as well as the presently used categorical forecast. Further, ESP has the advantage of providing at least a qualitative measure of the uncertainty in the forecasts, with probability forecasts being the ultimate goal.

  • 15. Nishiyama, Koji
    et al.
    Endo, Shinichi
    Jinno, Kenji
    Uvo, Cintia Bertacchi
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Berndtsson, Ronny
    Identification of typical synoptic patterns causing heavy rainfall in the rainy season in Japan by a Self-Organizing Map2007In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 83, no 2-4, p. 185-200Article in journal (Refereed)
    Abstract [en]

    In order to systematically and visually understand well-known but qualitative and complex relationships between synoptic fields and heavy rainfall events in Kyushu Islands, southwestern Japan, during the BAIU season, these synoptic fields were classified using the Self-Organizing Map (SOM), which can convert complex non-linear features into simple two-dimensional relationships. It was assumed that the synoptic field patterns could be simply expressed by the spatial distribution of (1) wind components at the 850 hPa level and (2) precipitable water (PW) defined by the water vapor amount contained in a vertical column of the atmosphere. By the SOM algorithm and the clustering techniques of the U-matrix and the K-means, the synoptic fields could be divided into eight kinds of patterns (clusters). One of the clusters has the notable spatial features represented by a large PW content accompanied by strong wind components known as low-level jet (LLJ). The features of this cluster indicate a typical synoptic field pattern that frequently causes heavy rainfall in Kyushu during the rainy season. In addition, an independent data set was used for validating the performance of the trained SOM. The results indicated that the SOM could successfully extract heavy rainfall events related to typical synoptic field patterns of the BAIU season. Interestingly, one specific SOM unit was closely related to the occurrence of disastrous heavy rainfall events observed during both training and validation periods. From these results, the trained SOM showed good performance for identifying synoptic fields causing heavy rainfall also in the validation period. We conclude that the SOM technique may be an effective tool for classifying complicated non-linear synoptic fields and identifying heavy rainfall events to some degree. (c) 2006 Elsevier B.V. All rights reserved.

  • 16.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Spatio-temporal precipitation error propagation in runoff modelling: a case study in central Sweden2006In: Natural hazards and earth system sciences, ISSN 1561-8633, E-ISSN 1684-9981, Vol. 6, no 4, p. 597-609Article in journal (Refereed)
    Abstract [en]

    The propagation of spatio-temporal errors in precipitation estimates to runoff errors in the output from the conceptual hydrological HBV model was investigated. The study region was the Giman catchment in central Sweden, and the period year 2002. Five precipitation sources were considered: NWP model (H22), weather radar (RAD), precipitation gauges (PTH), and two versions of a mesoscale analysis system (M11, M22). To define the baseline estimates of precipitation and runoff, used to define seasonal precipitation and runoff biases, the mesoscale climate analysis M11 was used. The main precipitation biases were a systematic overestimation of precipitation by H22, in particular during winter and early spring, and a pronounced local overestimation by RAD during autumn, in the western part of the catchment. These overestimations in some cases exceeded 50% in terms of seasonal subcatchment relative accumulated volume bias, but generally the bias was within +/- 20%. The precipitation data from the different sources were used to drive the HBV model, set up and calibrated for two stations in Giman, both for continuous simulation during 2002 and for forecasting of the spring flood peak. In summer, autumn and winter all sources agreed well. In spring H22 overestimated the accumulated runoff volume by similar to 50% and peak discharge by almost 100%, owing to both overestimated snow depth and precipitation during the spring flood. PTH overestimated spring runoff volumes by similar to 15% owing to overestimated winter precipitation. The results demonstrate how biases in precipitation estimates may exhibit a substantial space-time variability, and may further become either magnified or reduced when applied for hydrological purposes, depending on both temporal and spatial variations in the catchment. Thus, the uncertainty in precipitation estimates should preferably be specified as a function of both time and space.

  • 17.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Amaguchi, Hideo
    Alsterhag, Elin
    Daverhog, Maria
    Adrian, Per-Erik
    Kawamura, Akira
    Adaptation to climate change impacts on urban storm water: a case study in Arvika, Sweden2013In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 116, no 2, p. 231-247Article in journal (Refereed)
    Abstract [en]

    Already today, the functionality of many sewer and storm water systems are not up to the required standards and consequently flooding problems are experienced in case of heavy storms. System upgrades are required, which are however complicated by the expected future increase in short-term rainfall intensities as a result of climate change. In this case study, focusing on the town of Arvika, Sweden, this issue is investigated in three main steps. In the first, extreme value analyses of 30-min rainfall from an ensemble of climate projections are carried out to estimate the future increase and generate a future design storm. In the second, the existing system's response to both today's and future design storms are simulated by a coarse sewer model setup (MOUSE) and a detailed coupled surface-sewer model setup (TSR). In the third and final step, system upgrades are designed and evaluated by both models. The results indicate an increase by 10-30 % of today's short-term rainfall extremes by the end of the century. Upgrading the system to achieve a satisfactory performance for the future design storm would cost approximately twice as much as an upgrade based on today's design storm.

  • 18.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Borris, Matthias
    Donnelly, Chantal
    SMHI, Research Department, Hydrology.
    Foster, Kean
    SMHI, Research Department, Hydrology.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Persson, Magnus
    SMHI.
    Perttu, Anna-Maria
    Uvo, Cintia B.
    Viklander, Maria
    Yang, Wei
    SMHI, Research Department, Hydrology.
    Hydrological Climate Change Impact Assessment at Small and Large Scales: Key Messages from Recent Progress in Sweden2016In: CLIMATE, ISSN 2225-1154, Vol. 4, no 3, article id 39Article in journal (Refereed)
  • 19.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Borris, Matthias
    Donnelly, Chantal
    SMHI, Research Department, Hydrology.
    Foster, Kean
    SMHI, Research Department, Hydrology.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Persson, Magnus
    Perttu, Anna-Maria
    Uvo, Cintia B.
    Viklander, Maria
    Yang, Wei
    SMHI, Research Department, Hydrology.
    Hydrological Climate Change Impact Assessment at Small and Large Scales: Recent Progress and Current Issues.2016In: Climate, ISSN 2225-1154, Vol. 4(3), no 39Article in journal (Refereed)
  • 20.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Berg, Peter
    SMHI, Research Department, Hydrology.
    Eronn, Anna
    SMHI, Research Department, Climate research - Rossby Centre.
    Simonsson, Lennart
    SMHI, Research Department, Hydrology.
    Södling, Johan
    SMHI, Professional Services.
    Wern, Lennart
    SMHI, Core Services.
    Yang, Wei
    SMHI, Research Department, Hydrology.
    Extremregn i nuvarande och framtida klimat Analyser av observationer och framtidsscenarier2018Report (Other academic)
    Abstract [sv]

    Studien har främst omfattat analyser av extrem korttidsnederbörd i observationer från SMHIs nät av automatiska meteorologiska stationer. Även analyser av korttidsnederbörd från kommunala mätare, manuella meteorologiska stationer, väderradar och klimatmodeller har genomförts. De huvudsakliga slutsatserna från detta uppdrag kan sammanfattas enligt följande.

    • En regionalisering av extrem korttidsnederbörd (skyfall) i Sverige gav fyra regioner: sydvästra (SV), sydöstra (SÖ), mellersta (M) och norra (N) Sverige. Ytterligare indelning kan göras men i denna studie prioriterades att ha regioner av denna storleksordning för att få ett ordentligt underlag för regional statistik. Regionaliseringen gäller enbart korttidsnederbörd, upp till maximalt 12 tim varaktighet.
    • Den regionala statistiken uppvisar tämligen distinkta geografiska skillnader, med högst värden i region SV och lägst i region N. Det är inte förvånande att vårt avlånga land uppvisar regionala skillnader då varmare och fuktigare luftmassor förekommer mer i söder än i norr, och därmed ökar förutsättningarna för intensiv nederbörd. Den regionala statistiken överensstämmer överlag väl med motsvarande statistik i våra grannländer.
    • Under perioden 1996-2017 finns inga tydliga tidsmässiga tendenser vad gäller skyfallens storlek och frekvens i de olika regionerna, utan dessa ligger överlag på en konstant nivå. Inte heller extrem dygnsnederbörd sedan 1900 uppvisar några tydliga tendenser på regional nivå. På nationell nivå indikeras en svag ökning av dels landets högsta årliga nederbörd sedan 1881, dels förekomsten av stora, utbredda 2-dygnsregn sedan 1961.
    • Skyfallsstatistik baserad på nederbördsobservationer från väderradar som justerats mot interpolerade stationsdata (HIPRAD) överensstämmer väl med stationsbaserad statistik för korta varaktigheter (upp till 2 tim) i södra Sverige. För längre varaktigheter och i mellersta och norra Sverige överskattar HIPRAD regnvolymerna.
    • Analyser av de senaste klimatmodellerna (Euro-CORDEX) indikerar en underskattning av extrema regnvolymer för korta varaktigheter (1 tim) men överlag en realistisk beskrivning av observerad skyfallsstatistik. Den framtida ökningen av volymerna beräknas ligga mellan 10% och 40% beroende på tidshorisont och koncentration av växthusgaser, vilket överlag ligger nära tidigare bedömningar.

    Både för bedömningen av regionala skillnader och historiska klimateffekter är det av största vikt att bibehålla, eller ännu hellre utöka, observationerna av korttidsnederbörd i Sverige. Nederbördsmätning via alternativa tekniker bör kunna användas i allt högre utsträckning framöver för förbättrad kunskap och statistik. Väderradar är redan etablerat och den digitala utvecklingen öppnar även möjligheter till insamling av nederbördsdata och relaterad information via mobilmaster, uppkopplade privata väderstationer, sociala medier, etc. Denna utveckling måste bevakas, utvärderas och i största möjliga utsträckning utnyttjas.

  • 21.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Berg, Peter
    SMHI, Research Department, Hydrology.
    Kawamura, Akira
    Impact of RCM Spatial Resolution on the Reproduction of Local, Subdaily Precipitation2015In: Journal of Hydrometeorology, ISSN 1525-755X, E-ISSN 1525-7541, Vol. 16, no 2, p. 534-547Article in journal (Refereed)
    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.

  • 22.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Berggren, K.
    Olofsson, M.
    Viklander, M.
    Applying climate model precipitation scenarios for urban hydrological assessment: A case study in Kalmar City, Sweden2009In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 92, no 3, p. 364-375Article in journal (Refereed)
    Abstract [en]

    There is growing interest in the impact of climate change on urban hydrological processes. Such assessment may be based on the precipitation output from climate models. To date, the model resolution in both time and space has been too low for proper assessment, but at least in time the resolution of available model output is approaching urban scales. In this paper, 30-min precipitation from a model grid box covering Kalmar City, Sweden, is compared with high-resolution (tipping-bucket) observations from a gauge in Kalmar. The model is found to overestimate the frequency of low rainfall intensities, and therefore the total volume, but reasonably well reproduce the highest intensities. Adapting climate model data to urban drainage applications can be done in several ways but a popular way is the so-called Delta Change (DC) method. In this method, relative changes in rainfall characteristics estimated from climate model output are transferred to an observed rainfall time series, generally by multiplicative factors. In this paper, a version of the method is proposed in which these DC factors (DCFs) are related to the rainfall intensity level. This is achieved by calculating changes in the probability distribution of rainfall intensities and modelling the DCFs as a function of percentile. Applying this method in Kalmar indicated that in summer and autumn, high intensities will increase by 20-60% by year 2100, whereas low intensities remain stable or decrease. In winter and spring, generally all intensity levels increase similarly. The results were transferred to the observed time series by varying the volume of the tipping bucket to reflect the estimated intensity changes on a 30-min time scale. In an evaluation of the transformed data at a higher 5-min resolution, effects on the intensity distribution as well as single precipitation events were demonstrated. In particular, qualitatively different changes in peak intensity and total volume are attainable, which is required in light of expected future changes of the precipitation process and a step forward as compared with simpler DC approaches. Using the DC transformed data as input in urban drainage simulations for a catchment in Kalmar indicated an increase of the number of surface floods by 20-45% during this century. (C) 2009 Elsevier B.V. All rights reserved.

  • 23.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Burlando, P
    Reproduction of temporal scaling by a rectangular pulses rainfall model2002In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 16, no 3, p. 611-630Article in journal (Refereed)
    Abstract [en]

    The presence of scaling statistical properties in temporal rainfall has been well established in many empirical investigations during the latest decade. These properties have more and more come to be regarded as a fundamental feature of the rainfall process. How to best use the scaling properties for applied modelling remains to be assessed, however, particularly in the case of continuous rainfall time-series. One therefore is forced to use conventional time-series modelling, e.g. based on point process theory, which does not explicitly take scaling into account. In light of this, there is a need to investigate the degree to which point-process models are able to unintentionally reproduce the empirical scaling properties. In the present study, four 25-year series of 20-min rainfall intensities observed in Arno River basin, Italy, were investigated. A Neyman-Scott rectangular pulses (NSRP) model was fitted to these series, so enabling the generation of synthetic time-series suitable for investigation. A multifractal scaling behaviour was found to characterize the raw data within a range of time-scales between approximately 20 min and 1 week. The main features of this behaviour were surprisingly well reproduced in the simulated data, although some differences were observed, particularly at small scales below the typical duration of a rain cell. This suggests the possibility of a combined use of the NSRP model and a scaling approach, in order to extend the NSRP range of applicability for simulation purposes, Copyright (C) 2002 John Wiley Sons, Ltd.

  • 24.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Dahné, Joel
    SMHI, Professional Services.
    German, Jonas
    SMHI.
    Westergren, Bo
    Stockholm Vatten AB.
    von Scherling, Mathias
    Stockholm Vatten AB.
    Kjellson, Lena
    Stockholm Vatten AB.
    Olsson, Alf
    Sweco AB.
    En studie av framtida flödesbelastning på Stockholms huvudavloppssystem2011Report (Other academic)
    Abstract [en]

    This study was performed within the SWEdish research programme on Climate, Impacts and Adaptation (SWECIA), funded by the Foundation for Strategic Environmental Research (MISTRA), with additional funding from Stockholm Vatten AB. The aim of the study was to assess the discharge load on Stockholm's main sewer system during the rest of this century in light of both climate change and population increase. For this assessment, flow simulations with MIKE Urban were performed. Reference simulations for today's climate were done both for a representative year (1984) and for some 200 selected rainfall events between 1983 and 2007. In future simulations the climate effect was taken into account by rescaling input data (temperature, precipitation, evaporation) in line with climate model scenarios and the population effect by an increase in line with official estimations. The results indicate in particular that the spill volumes to Lake Mälaren and Saltsjön will increase substantially, but also an increased inflow to the treatment plant, and thus an increased need for treatment, and an increased flood risk.

  • 25.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Foster, Kean
    SMHI, Research Department, Hydrology.
    Extrem korttidsnederbörd i klimatprojektioner för Sverige2013Report (Other academic)
    Abstract [en]

    Climate change is expected to generate higher short-term precipitation intensities, which may have negative consequences for e.g. urban hydrology. In this study, extreme short-term precipitation in simulations with the RCA3 regional climate model for Sweden are analysed. An observed weak increase in the 10-year daily precipitation from 1961-1990 to 1981-2010 is qualitatively reproduced in RCA3 simulations forced with both meteorological re-analyses and an ensemble of six global climate projections. This does not guarantee that estimated future changes are correct, but indicates an ability of the model to describe changes in daily extremes when appropriate boundary conditions are used. In the ensemble of future projections, from 1981-2010 the 10-year 30-min precipitation will increase by 6% until 2011-2040, 15% until 2041-2070 and 23% until 2071-2100. The increase decreases with increasing duration and at the daily scale the percentage values are approximately halved. Assessment of the impacts on the results of both the specific RCM used (RCA3) and its spatial resolution (50 km) suggested possibilities of both lower and higher future changes.A synthesis of the work on future short-term precipitation extremes performed in Sweden to date suggests an expected 10% increase of the intensity related to very short durations (≤ 1 h) until 2050 and a 25% increase until 2100. Low and high estimates are suggested to be ±10 percentage points from the expected values but also larger deviations are possible. For duration 1 day, the increase is estimated to become five percentage points lower.

  • 26.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Foster, Kean
    SMHI, Research Department, Hydrology.
    Short-term precipitation extremes in regional climate simulations for Sweden2014In: HYDROLOGY RESEARCH, ISSN 1998-9563, Vol. 45, no 3, p. 479-489Article in journal (Refereed)
    Abstract [en]

    Climate change is expected to generate higher short-term precipitation intensities, which may have negative consequences in terms of, for example, increased risk of flooding and sewer overflow. In this study, extreme precipitation for durations between 30 min and 1 day in simulations with the RCA3 regional climate model (RCM) for Sweden are analysed. As compared with daily observations in the period 1961-2010, the simulated extremes are found to be overall realistic with respect to magnitude, spatial homogeneity and temporal variability. In the ensemble of future projections, from 1981 to 2010 the 10-year 30-min precipitation will increase by 6% until 2011-2040, 15% until 2041-2070 and 23% until 2071-2100. The increase decreases with increasing duration and at the daily scale the percentage values are approximately halved. The values are largely consistent with earlier estimates. Assessment of the impacts on the results of the spatial resolution and the specific RCM used indicated possibilities of both smaller and larger future increases.

  • 27.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Gidhagen, Lars
    SMHI, Research Department, Air quality.
    Gamerith, Valentin
    Gruber, Gunter
    Hoppe, Holger
    Kutschera, Peter
    Downscaling of Short-Term Precipitation from Regional Climate Models for Sustainable Urban Planning2012In: Sustainability, ISSN 2071-1050, E-ISSN 2071-1050, Vol. 4, no 5, p. 866-887Article in journal (Refereed)
    Abstract [en]

    A framework for downscaling precipitation from RCM projections to the high resolutions in time and space required in the urban hydrological climate change impact assessment is outlined and demonstrated. The basic approach is that of Delta Change, developed for both continuous and event-based applications. In both cases, Delta Change Factors (DCFs) are calculated which represent the expected future change of some key precipitation statistics. In the continuous case, short-term precipitation from climate projections are analysed in order to estimate DCFs associated with different percentiles in the frequency distribution of non-zero intensities. The DCFs may then be applied to an observed time series, producing a realisation of a future time series. The event-based case involves downscaling of Intensity-Duration-Frequency (IDF) curves based on extreme value analysis of annual maxima using the Gumbel distribution. The resulting DCFs are expressed as a function of duration and frequency (i.e., return period) and may be used to estimate future design storms. The applications are demonstrated in case studies focusing on the expected changes in short-term precipitation statistics until 2100 in the cities of Linz (Austria) and Wuppertal (Germany). The downscaling framework is implemented in the climate service developed within the EU-project SUDPLAN.

  • 28.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Graham, Phil
    SMHI, Professional Services.
    Rosberg, Jörgen
    SMHI, Research Department, Hydrology.
    Hellström, Sara-Sofia
    SMHI, Research Department, Hydrology.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Berndtsson, Ronny
    Lund University, Department of Water Resources Engineering, .
    Simulation of Runoff in the Baltic Sea Drainage Basin During the Past Millennium2007Conference paper (Other academic)
  • 29.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Josefsson, Weine
    SMHI, Core Services.
    Skyfallsuppdraget ett regeringsuppdrag till SMHI2015Report (Other academic)
    Abstract [en]

    Arbetet har sammanfattats i en rapport, som kan betraktas som en lägesrapport, inkluderar en omvärldsanalys; vad som gjorts i Sverige och i andra länder, delvis inhämtat vid en expertworkshop. Rapporten innehåller också en bearbetning av SMHIs nederbördsobservationer avseende korttidsnederbörd (skyfall) och en diskussion kring olika statistiska metoder att analysera dessa observationer. Dessutom har SMHIs nuvarande system för att prognosera skyfall uppgraderats och i rapporten diskuteras även vilka möjligheter som finns att ytterligare förbättra prognoserna i framtiden. Den pågående klimatförändringen påverkar vädret och därmed skyfallen. Rapporten tar upp de senaste rönen inom forskningen och även de negativa effekter som skyfall ger på samhället. Vilka behov finns i samhället och vad kan vi göra för att minimera de negativa effekterna var något som diskuterades vid en användarworkshop.

  • 30.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Lindström, Göran
    SMHI, Research Department, Hydrology.
    Evaluation and calibration of operational hydrological ensemble forecasts in Sweden2008In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 350, no 1-2, p. 14-24Article in journal (Refereed)
    Abstract [en]

    Daily operational hydrological 9-day ensemble forecasts during 18 months in 45 catchments were evaluated in probabilistic terms. The forecasts were generated by using ECMWF meteorological ensemble forecasts as input to the HBV model, set up and calibrated for each catchment. Two kinds of reference discharges were used in the evaluation, "perfect forecasts" and actual discharge observations. A percentile-based evaluation indicated that the ensemble spread is underestimated, with a degree that decreases with increasing lead time. The share of this error related to hydrological model uncertainty was found to be similar in magnitude to the share related to underdispersivity in the ECMWF meteorological forecasts. A threshold-based evaluation indicated that the probability of exceeding a high discharge threshold is generally overestimated in the ensemble forecasts, with a degree that increases with probability level. In this case the contribution to the error from the meteorological forecasts is larger than the contribution from the hydrological model. A simple calibration method to adjust the ensemble spread by bias correction of ensemble percentiles was formulated and tested in five catchments. The method substantially improved the ensemble spread in all tested catchments, and the adjustment parameters were found to be reasonably well estimated as simple functions of the mean catchment discharge. (c) 2007 Elsevier B.V. All rights reserved.

  • 31.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Lindström, Göran
    SMHI, Research Department, Hydrology.
    Johnell, Anna
    SMHI, Professional Services.
    Jacobsson, Karin
    SMHI, Professional Services.
    Hydrologiska ensembleprognoser2006Report (Other academic)
    Abstract [en]

    Since July 2004, a system for hydrological ensemble forecasting has been operational at SMHI. The system uses meteorological ensemble forecasts of precipitation and temperature from ECMWF as input to the hydrological HBV model, which generates an ensemble of discharge forecasts. In this report, the hydrological ensemble prediction system (EPS) is firstly described, along with some general features of the forecasts. Some preparatory analyses of the ECMWF meteorological forecasts and spring flood EPS forecasts are made. The main part of the report is an evaluation of 18 months of 9-day hydrological ensemble forecasts in 45 Swedish catchments. In the deterministic evaluation, the EPS median forecast is compared with the categorical PMP forecast. The results indicate an overall similar performance of the two forecast types. It is also shown that the spread of the EPS forecasts is related to the forecast error. In the probabilistic evaluation, the accuracy of probabilities calculated from the EPS spread is investigated. A percentile-based evaluation shows that the spread is underestimated. A threshold-based evaluation shows that the probability of exceeding some high discharge threshold level is overestimated. Finally, a simple method to correct the EPS spread is developed and tested, and different ways to present EPS forecasts are discussed.

  • 32.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Pers, Charlotta
    SMHI, Research Department, Hydrology.
    Bengtsson, Lisa
    SMHI, Research Department, Meteorology.
    Pechlivanidis, Ilias
    SMHI, Research Department, Hydrology.
    Berg, Peter
    Körnich, Heiner
    SMHI, Research Department, Meteorology.
    Distance-dependent depth-duration analysis in high-resolution hydro-meteorological ensemble forecasting: A case study in Malmo City, Sweden2017In: Environmental Modelling & Software, ISSN 1364-8152, E-ISSN 1873-6726, Vol. 93, p. 381-397Article in journal (Refereed)
  • 33.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Persson, M
    Albergel, J
    Berndtsson, R
    Zante, P
    Ohrstrom, P
    Nasri, S
    Multiscaling analysis and random cascade modeling of dye infiltration2002In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 38, no 11, article id 1263Article in journal (Refereed)
    Abstract [en]

    [1] We aimed at investigating whether the spatial variability of infiltration in field soils, as visualized through dye infiltration experiments, is characterized by a multiscaling behavior. Digitized high-resolution dye images from three sites in an experimental catchment in Tunisia were analyzed using three indicators of scaling: empirical probability distribution functions, power spectra, and raw statistical moments. The two former indicators suggested a general scaling behavior of the data, which through the moments' analysis was found to be of multiscaling type. Random cascade processes are frequently used to model multiscaling processes, and we fitted the "universal multifractal'' (UM) model of Schertzer and Lovejoy [1987] to our data. The UM model closely reproduced the empirical K(q) functions, and simulated fields reproduced key features in the observed ones. The results indicate that multiscaling random cascade modeling is useful for statistically describing flow processes and solute transport under field conditions.

  • 34.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Persson, Magnus
    Jinno, Kenji
    Analysis and modeling of solute transport dynamics by breakdown coefficients and random cascades2007In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 43, no 3, article id W03417Article in journal (Refereed)
    Abstract [en]

    The small-scale variability and scaling properties of solute transport dynamics were investigated by laboratory experiments. Dye-stained water was applied at a constant flux in a Plexiglas Hele-Shaw cell filled with soil material, and the transport process was registered by digital photographs of the cell front, producing a very high resolution in both time (minutes) and space (millimeters). The experiments comprised different cell materials (uniform and natural sand) and different water fluxes. Scaling properties of vertically integrated dye mass distributions were analyzed and modeled using so-called breakdown coefficients (BDCs), which represent the multiplicative weights in a microcanonical random cascade process. The pdfs of BDCs varied with scale, indicating self-affine scaling, and were accurately approximated by beta distributions with a scaling parameter. Two versions of BDC-based random cascade models were used to simulate mass distributions at different time steps. The results support the applicability of random cascade models to subsurface transport processes.

  • 35.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Simonsson, Lennart
    SMHI, Research Department, Hydrology.
    Ridal, Martin
    SMHI, Research Department, Meteorology.
    Rainfall nowcasting: predictability of short-term extremes in Sweden2015In: Urban Water Journal, ISSN 1573-062X, Vol. 12, no 1, p. 3-13Article in journal (Refereed)
    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.

  • 36.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Simonsson, Lennart
    SMHI, Research Department, Hydrology.
    Ridal, Martin
    SMHI, Research Department, Meteorology.
    Rainfall nowcasting: predictability of short-term extremes in Sweden2014In: Urban Water Journal, ISSN 1573-062X, Vol. 11, no 7, p. 605-615Article in journal (Refereed)
    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,,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.

  • 37.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Södling, Johan
    SMHI, Professional Services.
    Wetterhall, Fredrik
    SMHI, Research Department, Hydrology.
    Högupplösta nederbördsdata för hydrologisk modellering: en förstudie2013Report (Other academic)
    Abstract [en]

    Hydrological modeling at SMHI is generally done with a daily time step. However, today simulation and forecasting with a shorter time step is possible, through a spatially highly resolved hydrological model (S-HYPE) as well as high-resolution input data. In this preliminary study, different types of observation-based, high-resolution input data (mainly precipitation) have been invented, compiled and evaluated at different temporal and spatial scales: automatic stations, PTHBV, MESAN, radar data. A new product called PTHBV-radar has been developed by distributing the daily precipitation in PTHBV over the day using radar observations. The different types of data were tested in hydrological simulation by the HYPE model in a small catchment.For long accumulation times (year, month) PTHBV gives higher values than MESAN. Radar data have distinct artifacts, e.g. in the border between radars, but regional mean values agree with other sources. Concerning 1-h precipitation, the overall agreement with automatic station data is best in MESAN, followed by PTHBV-radar and radar. The spatial smoothing in MESAN however generates lower values of maximum intensities, in this respect PTHBV-radar and radar are closer to the station data.The hydrological 1-h simulations with MESAN and PTHBV-radar as input data improved performance evaluated on a daily basis, as compared with a reference simulation with PTHBV as input data. Using radar precipitation as input generated an overestimated discharge. The differences between 1-d and 1-h simulations were illustrated for single high flows and in terms of maximum daily values.

  • 38.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Uvo, C. B.
    Foster, Kean
    SMHI, Research Department, Hydrology.
    Yang, Wei
    SMHI, Research Department, Hydrology.
    Technical Note: Initial assessment of a multi-method approach to spring-flood forecasting in Sweden2016In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 20, no 2, p. 659-667Article in journal (Refereed)
    Abstract [en]

    Hydropower is a major energy source in Sweden, and proper reservoir management prior to the spring-flood onset is crucial for optimal production. This requires accurate forecasts of the accumulated discharge in the spring-flood period (i.e. the spring-flood volume, SFV). Today's SFV forecasts are generated using a model-based climatological ensemble approach, where time series of precipitation and temperature from historical years are used to force a calibrated and initialized set-up of the HBV model. In this study, a number of new approaches to spring-flood forecasting that reflect the latest developments with respect to analysis and modelling on seasonal timescales are presented and evaluated. Three main approaches, represented by specific methods, are evaluated in SFV hindcasts for the Swedish river Vindelalven over a 10-year period with lead times between 0 and 4 months. In the first approach, historically analogue years with respect to the climate in the period preceding the spring flood are identified and used to compose a reduced ensemble. In the second, seasonal meteorological ensemble forecasts are used to drive the HBV model over the spring-flood period. In the third approach, statistical relationships between SFV and the large-sale atmospheric circulation are used to build forecast models. None of the new approaches consistently outperform the climatological ensemble approach, but for early forecasts improvements of up to 25% are found. This potential is reasonably well realized in a multi-method system, which over all forecast dates reduced the error in SFV by similar to 4 %. This improvement is limited but potentially significant for e.g. energy trading.

  • 39.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Uvo, C B
    Jinno, K
    Kawamura, A
    Nishiyama, K
    Koreeda, N
    Nakashima, T
    Morita, O
    Neural networks for rainfall forecasting by atmospheric downscaling2004In: Journal of hydrologic engineering, ISSN 1084-0699, E-ISSN 1943-5584, Vol. 9, no 1, p. 1-12Article in journal (Refereed)
    Abstract [en]

    Several studies have used artificial neural networks (NNs) to estimate local or regional precipitation/rainfall on the basis of relationships with coarse-resolution atmospheric variables. None of these experiments satisfactorily reproduced temporal intermittency and variability in rainfall. We attempt to improve performance by using two approaches: (1) couple two NNs in series, the first to determine rainfall occurrence, and the second to determine rainfall intensity during rainy periods; and (2) categorize rainfall into intensity categories and train the NN to reproduce these rather than the actual intensities. The experiments focused on estimating 12-h mean rainfall in the Chikugo River basin, Kyushu Island, southern Japan, from large-scale values of wind speeds at 850 hPa and precipitable water. The results indicated that (1) two NNs in series may greatly improve the reproduction of intermittency; (2) longer data series are required to reproduce variability; (3) intensity categorization may be useful for probabilistic forecasting; and (4) overall performance in this region is better during winter and spring than during summer and autumn.

  • 40. Pechlivanidis, Ilias G.
    et al.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Bosshard, Thomas
    SMHI, Research Department, Hydrology.
    Sharma, Devesh
    Sharma, K. C.
    Multi-Basin Modelling of Future Hydrological Fluxes in the Indian Subcontinent2016In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 8, no 5, article id 177Article in journal (Refereed)
    Abstract [en]

    The impact of climate change on the hydro-climatology of the Indian subcontinent is investigated by comparing statistics of current and projected future fluxes resulting from three RCP scenarios (RCP2.6, RCP4.5, and RCP8.5). Climate projections from the CORDEX-South Asia framework have been bias-corrected using the Distribution-Based Scaling (DBS) method and used to force the HYPE hydrological model to generate projections of evapotranspiration, runoff, soil moisture deficit, snow depth, and applied irrigation water to soil. We also assess the changes in the annual cycles in three major rivers located in different hydro-climatic regions. Results show that conclusions can be influenced by uncertainty in the RCP scenarios. Future scenarios project a gradual increase in temperature (up to 7 degrees C on average), whilst changes (both increase and decrease) in the long-term average precipitation and evapotranspiration are more severe at the end of the century. The potential change (increase and decrease) in runoff could reach 100% depending on the region and time horizon. Analysis of annual cycles for three selected regions showed that changes in discharge and evapotranspiration due to climate change vary between seasons, whereas the magnitude of change is dependent on the region's hydro-climatic gradient. Irrigation needs and the snow depth in the Himalayas are also affected.

  • 41. Pechlivanidis, Ilias G.
    et al.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Bosshard, Thomas
    SMHI, Research Department, Hydrology.
    Sharma, Devesh
    Sharma, K. C.
    Multi-Basin Modelling of Future Hydrological Fluxes in the Indian Subcontinent2016In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 8, no 5, p. 177-177Article in journal (Refereed)
    Abstract [en]

    The impact of climate change on the hydro-climatology of the Indian subcontinent is investigated by comparing statistics of current and projected future fluxes resulting from three RCP scenarios (RCP2.6, RCP4.5, and RCP8.5). Climate projections from the CORDEX-South Asia framework have been bias-corrected using the Distribution-Based Scaling (DBS) method and used to force the HYPE hydrological model to generate projections of evapotranspiration, runoff, soil moisture deficit, snow depth, and applied irrigation water to soil. We also assess the changes in the annual cycles in three major rivers located in different hydro-climatic regions. Results show that conclusions can be influenced by uncertainty in the RCP scenarios. Future scenarios project a gradual increase in temperature (up to 7 degrees C on average), whilst changes (both increase and decrease) in the long-term average precipitation and evapotranspiration are more severe at the end of the century. The potential change (increase and decrease) in runoff could reach 100% depending on the region and time horizon. Analysis of annual cycles for three selected regions showed that changes in discharge and evapotranspiration due to climate change vary between seasons, whereas the magnitude of change is dependent on the region's hydro-climatic gradient. Irrigation needs and the snow depth in the Himalayas are also affected.

  • 42.
    Pechlivanidis, Ilias
    et al.
    SMHI, Research Department, Hydrology.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Sharma, D.
    Bosshard, Thomas
    SMHI, Research Department, Hydrology.
    Sharma, K. C.
    ASSESSMENT OF THE CLIMATE CHANGE IMPACTS ON THE WATER RESOURCES OF THE LUNI REGION, INDIA2015In: GLOBAL NEST JOURNAL, ISSN 1790-7632, Vol. 17, no 1, p. 29-40Article in journal (Refereed)
    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.

  • 43. Persson, M
    et al.
    Haridy, S
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Wendt, J
    Solute transport dynamics by high-resolution dye tracer experiments - Image analysis and time moments2005In: Vadose Zone Journal, ISSN 1539-1663, E-ISSN 1539-1663, Vol. 4, no 3, p. 856-865Article in journal (Refereed)
    Abstract [en]

    Accurate measurements of solute concentration are needed to conduct studies of solute transport process in unsaturated soil. In this paper we present a method of obtaining accurate measurements in and space using dye infiltration and image analysis. The soil color was related to the dye concentration in the soil (C-s) using 74 small calibration samples. The overall root mean square error (RMSE) 0.057 g dm(-3), however, for C-s < 0.75 g dm(-3), the RMSE was only 0.032 g dm(-3). Variability of the concentration estimates at the pixel scale could be reduced by using an average filter. We used the calibration relationship during four infiltration experiments in a 0.95 by 0.975 m large Plexiglas Hele-Shaw cell to calculate dye concentration patterns. Using the first and second order time moments, the dispersivity lambda was calculated for nine different artificial column widths, from 0.0014 (local-scale) to 0.72 m (meso-scale). The horizontally averaged lambda proved to be identical for column widths from 0.0014 to 0.045 m. For larger scales, lambda gradually increased. We noticed that the two experiments with higher flow (1 and 2) and the two experiments with lower flow (3 and 4) showed an almost identical variation of meso-scale lambda with depth. We concluded that above a specific critical value of theta (similar to 0.22 m(3) m(-3)), solute mixing is enhanced, leading to a lower lambda, and that solute transport can be described as a convective-dispersive process. When theta is lower than this critical level, part of the porosity is deactivated and mixing between individual stream tubes decreases, which implies that transport then occurs as a stochastic-convective process.

  • 44. Persson, Magnus
    et al.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Scaling analyses of high-resolution dye tracer experiments2008In: Hydrological Sciences Journal, ISSN 0262-6667, E-ISSN 2150-3435, Vol. 53, no 6, p. 1286-1299Article in journal (Refereed)
    Abstract [en]

    Four unsaturated solute transport experiments with different water fluxes were conducted in a Hele-Shaw cell filled with uniform sand. The transport of the dye tracer used was recorded with a camera and the dye concentration was calculated using image analysis. The concentrations fields were analysed in terms of time moments and converted into vertical solute transport velocity V. Both mean value and standard deviation of V increased with water flux. The autocorrelation function exhibited a linear decrease for short lags. The pronounced variability of V suggested a description in terms of scaling properties, and a scaling regime was indeed found from the resolution 1.8 mm up to almost 0.1 m. The upper limit corresponds roughly to a characteristic scale of fingering structures seen in the dye concentration images. Indications of a second scaling regime at larger scales were found. In the small-scale scaling regime, the power spectrum exponent beta was generally slightly below 1 and the intermittency parameter C(1) was on average 0.00025. The moment scaling K(q) functions were convex, implying a multiscaling process.

  • 45. Selim, Tarek
    et al.
    Persson, Magnus
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Impact of spatial rainfall resolution on point-source solute transport modelling2017In: Hydrological Sciences Journal, ISSN 0262-6667, E-ISSN 2150-3435, Vol. 62, no 16, p. 2587-2596Article in journal (Refereed)
  • 46. Willems, P.
    et al.
    Arnbjerg-Nielsen, K.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Nguyen, V. T. V.
    Climate change impact assessment on urban rainfall extremes and urban drainage: Methods and shortcomings2012In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 103, p. 106-118Article in journal (Refereed)
    Abstract [en]

    Cities are becoming increasingly vulnerable to flooding because of rapid urbanization, installation of complex infrastructure, and changes in the precipitation patterns caused by anthropogenic climate change. The present paper provides a critical review of the current state-of-the-art methods for assessing the impacts of climate change on precipitation at the urban catchment scale. Downscaling of results from global circulation models or regional climate models to urban catchment scales are needed because these models are not able to describe accurately the rainfall process at suitable high temporal and spatial resolution for urban drainage studies. The downscaled rainfall results are however highly uncertain, depending on the models and downscaling methods considered. This uncertainty becomes more challenging for rainfall extremes since the properties of these extremes do not automatically reflect those of average precipitation. In this paper, following an overview of some recent advances in the development of innovative methods for assessing the impacts of climate change on urban rainfall extremes as well as on urban hydrology and hydraulics, several existing difficulties and remaining challenges in dealing with this assessment are discussed and further research needs are described. (C) 2011 Elsevier B.V. All rights reserved.

  • 47.
    Yang, Wei
    et al.
    SMHI, Research Department, Hydrology.
    Andreasson, Johan
    SMHI, Professional Services.
    Graham, Phil
    SMHI, Research Department, Climate research - Rossby Centre.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Rosberg, Jörgen
    SMHI, Research Department, Hydrology.
    Wetterhall, Fredrik
    SMHI, Research Department, Hydrology.
    Distribution-based scaling to improve usability of regional climate model projections for hydrological climate change impacts studies2010In: HYDROLOGY RESEARCH, ISSN 1998-9563, Vol. 41, no 3-4, p. 211-229Article in journal (Refereed)
    Abstract [en]

    As climate change could have considerable influence on hydrology and corresponding water management, appropriate climate change inputs should be used for assessing future impacts. Although the performance of regional climate models (RCMs) has improved over time, systematic model biases still constrain the direct use of RCM output for hydrological impact studies. To address this, a distribution-based scaling (DBS) approach was developed that adjusts precipitation and temperature from RCMs to better reflect observations. Statistical properties, such as daily mean, standard deviation, distribution and frequency of precipitation days, were much improved for control periods compared to direct RCM output. DBS-adjusted precipitation and temperature from two IPCC Special Report on Emissions Scenarios (SRESA1B) transient climate projections were used as inputs to the HBV hydrological model for several river basins in Sweden for the period 1961-2100. Hydrological results using DBS were compared to results with the widely-used delta change (DC) approach for impact studies. The general signal of a warmer and wetter climate was obtained using both approaches, but use of DBS identified differences between the two projections that were not seen with DC. The DBS approach is thought to better preserve the future variability produced by the RCM, improving usability for climate change impact studies.

  • 48.
    Yang, Wei
    et al.
    SMHI, Research Department, Hydrology.
    Gardelin, Marie
    SMHI, Professional Services.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Bosshard, Thomas
    SMHI, Research Department, Hydrology.
    Multi-variable bias correction: application of forest fire risk in present and future climate in Sweden2015In: Natural hazards and earth system sciences, ISSN 1561-8633, E-ISSN 1684-9981, Vol. 15, no 9, p. 2037-2057Article in journal (Refereed)
    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.

1 - 48 of 48
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