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  • 201.
    Marklund, Lars
    et al.
    SMHI, Research Department, Hydrology.
    Worman, Anders
    The use of spectral analysis-based exact solutions to characterize topography-controlled groundwater flow2011In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 19, no 8, p. 1531-1543Article in journal (Refereed)
    Abstract [en]

    Spectral analysis enhances the ability to analyze groundwater flow at a steady state by separating the top boundary condition into its periodic forms. Specifically, spectral analysis enables comparisons of the impact of individual spatial scales on the total flow field. New exact spectral solutions are presented for analyzing 3D groundwater flow with an arbitrarily shaped top boundary. These solutions account for depth-decaying, anisotropic and layered permeability while utilizing groundwater flux or the phreatic surface as a top boundary condition. Under certain conditions, groundwater flow is controlled by topography. In areas where the groundwater flow is controlled by the topography, the unknown water table is often approximated by the topography. This approximation induces a systematic error. Here, the optimal resolution of digital elevation models (DEMs) is assessed for use as a top boundary in groundwater flow models. According to the analysis, the water-table undulation is smoother than the topography; therefore, there is an upper limit to the resolution of DEMs that should be used to represent the groundwater surface. The ability to represent DEMs of various spectral solutions was compared and the results indicate that the fit is strongly dependent on the number of harmonics in the spectral solution.

  • 202.
    Marmefelt, Eleonor
    et al.
    SMHI, Professional Services.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Langner, Joakim
    SMHI, Research Department, Air quality.
    An integrated biogeochemical model system for the Baltic Sea1999In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 393, p. 45-56Article in journal (Refereed)
    Abstract [en]

    The Swedish Meteorological and Hydrological Institute (SMHI) is developing an integrated biogeochemical model system for the Baltic Sea. It consists of three coupled models; a marine biogeochemical-hydrodynamical model (SCOBI), a continuous riverine nitrogen transport model (HBV-N) and an atmospheric transport and chemical model (MATCH). It is supplied with a tool for presentation and analysis. The SCOBI model is a coupled one-dimensional model with high vertical resolution. Horizontal variations are taken into account by dividing the area into smaller boxes. The model includes primary phytoplankton production, nitrogen fixation and secondary zooplankton production. Nitrogen load from land is obtained through the HBV-N model, which simulates organic and inorganic nitrogen separately in catchments. The model is based on the hydrological model HBV, and the subbasin runoff is simulated on a daily basis. The HBV-N model is calibrated and validated against measured concentrations and water flow in rivers. The atmospheric input of oxidised and reduced nitrogen is taken from the annual assessments carried out with the MATCH-Sweden modelling system. MATCH-Sweden combines model calculations, using an atmospheric transport and chemical model, with observations of air- and precipitation chemistry data to give a detailed mapping of concentrations and deposition of nitrogen compounds over Sweden. Supplemented with monitoring data for the specific area of interest, the integrated biogeochemical model system makes a useful tool for environmental protection analyses; e.g. for interpretation of monitoring data as well as creating scenarios for studies of effects in changes of the nutrient loads.

  • 203.
    Meier, Markus
    et al.
    SMHI, Research Department, Oceanography.
    Andersson, Helén
    SMHI, Research Department, Oceanography.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Blenckner, Thorsten
    Chubarenko, Boris
    Donnelly, Chantal
    SMHI, Research Department, Hydrology.
    Eilola, Kari
    SMHI, Research Department, Oceanography.
    Gustafsson, Bo G.
    Hansson, Anders
    Havenhand, Jonathan
    Höglund, Anders
    SMHI, Research Department, Oceanography.
    Kuznetsov, Ivan
    MacKenzie, Brian R.
    Muller-Karulis, Barbel
    Neumann, Thomas
    Niiranen, Susa
    Piwowarczyk, Joanna
    Raudsepp, Urmas
    Reckermann, Marcus
    Ruoho-Airola, Tuija
    Savchuk, Oleg P.
    Schenk, Frederik
    Schimanke, Semjon
    SMHI, Research Department, Oceanography.
    Vali, Germo
    Weslawski, Jan-Marcin
    Zorita, Eduardo
    Comparing reconstructed past variations and future projections of the Baltic Sea ecosystem-first results from multi-model ensemble simulations2012In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 7, no 3, article id 034005Article in journal (Refereed)
    Abstract [en]

    Multi-model ensemble simulations for the marine biogeochemistry and food web of the Baltic Sea were performed for the period 1850-2098, and projected changes in the future climate were compared with the past climate environment. For the past period 1850-2006, atmospheric, hydrological and nutrient forcings were reconstructed, based on historical measurements. For the future period 1961-2098, scenario simulations were driven by regionalized global general circulation model (GCM) data and forced by various future greenhouse gas emission and air-and riverborne nutrient load scenarios (ranging from a pessimistic 'business-as-usual' to the most optimistic case). To estimate uncertainties, different models for the various parts of the Earth system were applied. Assuming the IPCC greenhouse gas emission scenarios A1B or A2, we found that water temperatures at the end of this century may be higher and salinities and oxygen concentrations may be lower than ever measured since 1850. There is also a tendency of increased eutrophication in the future, depending on the nutrient load scenario. Although cod biomass is mainly controlled by fishing mortality, climate change together with eutrophication may result in a biomass decline during the latter part of this century, even when combined with lower fishing pressure. Despite considerable shortcomings of state-of-the-art models, this study suggests that the future Baltic Sea ecosystem may unprecedentedly change compared to the past 150 yr. As stakeholders today pay only little attention to adaptation and mitigation strategies, more information is needed to raise public awareness of the possible impacts of climate change on marine ecosystems.

  • 204.
    Meier, Markus
    et al.
    SMHI, Research Department, Oceanography.
    Andersson, Helén
    SMHI, Research Department, Oceanography.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Donnelly, Chantal
    SMHI, Research Department, Hydrology.
    Eilola, Kari
    SMHI, Research Department, Oceanography.
    Gustafsson, Bo G.
    Kotwicki, Lech
    Neset, Tina-Simone
    Niiranen, Susa
    Piwowarczyk, Joanna
    Savchuk, Oleg P.
    Schenk, Frederik
    Weslawski, Jan Marcin
    Zorita, Eduardo
    Ensemble Modeling of the Baltic Sea Ecosystem to Provide Scenarios for Management2014In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 43, no 1, p. 37-48Article in journal (Refereed)
    Abstract [en]

    We present a multi-model ensemble study for the Baltic Sea, and investigate the combined impact of changing climate, external nutrient supply, and fisheries on the marine ecosystem. The applied regional climate system model contains state-of-the-art component models for the atmosphere, sea ice, ocean, land surface, terrestrial and marine biogeochemistry, and marine food-web. Time-dependent scenario simulations for the period 1960-2100 are performed and uncertainties of future projections are estimated. In addition, reconstructions since 1850 are carried out to evaluate the models sensitivity to external stressors on long time scales. Information from scenario simulations are used to support decision-makers and stakeholders and to raise awareness of climate change, environmental problems, and possible abatement strategies among the general public using geovisualization. It is concluded that the study results are relevant for the Baltic Sea Action Plan of the Helsinki Commission.

  • 205. Merz, Bruno
    et al.
    Apel, Heiko
    Nguyen, Dung
    Falter, Daniela
    Guse, Björn
    Hundecha, Yeshewatesfa
    SMHI, Research Department, Hydrology.
    Kreibich, Heidi
    Schröter, Kai
    Vorogushyn, Sergiy
    From Precipitation to Damage: A Coupled Model Chain for Spatially Coherent, Large‐Scale Flood Risk AssessmentChapter 102018In: Global Flood Hazard: Applications in Modeling, Mapping, and Forecasting: Geophysical Monograph 233. AGU Publication / [ed] Guy J-P. Schumann, Paul D. Bates, Heiko Apel, and Giuseppe T. Aronica., John Wiley & Sons, 2018, First Edition, p. 169-183Chapter in book (Other academic)
  • 206. Montanari, A.
    et al.
    Young, G.
    Savenije, H. H. G.
    Hughes, D.
    Wagener, T.
    Ren, L. L.
    Koutsoyiannis, D.
    Cudennec, C.
    Toth, E.
    Grimaldi, S.
    Bloeschl, G.
    Sivapalan, M.
    Beven, K.
    Gupta, H.
    Hipsey, M.
    Schaefli, B.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Boegh, E.
    Schymanski, S. J.
    Di Baldassarre, G.
    Yu, B.
    Hubert, P.
    Huang, Y.
    Schumann, A.
    Post, D. A.
    Srinivasan, V.
    Harman, C.
    Thompson, S.
    Rogger, M.
    Viglione, A.
    McMillan, H.
    Characklis, G.
    Pang, Z.
    Belyaev, V.
    "Panta Rhei-Everything Flows": Change in hydrology and society-The IAHS Scientific Decade 2013-20222013In: Hydrological Sciences Journal, ISSN 0262-6667, E-ISSN 2150-3435, Vol. 58, no 6, p. 1256-1275Article in journal (Refereed)
    Abstract [en]

    The new Scientific Decade 2013-2022 of IAHS, entitled Panta RheiEverything Flows, is dedicated to research activities on change in hydrology and society. The purpose of Panta Rhei is to reach an improved interpretation of the processes governing the water cycle by focusing on their changing dynamics in connection with rapidly changing human systems. The practical aim is to improve our capability to make predictions of water resources dynamics to support sustainable societal development in a changing environment. The concept implies a focus on hydrological systems as a changing interface between environment and society, whose dynamics are essential to determine water security, human safety and development, and to set priorities for environmental management. The Scientific Decade 2013-2022 will devise innovative theoretical blueprints for the representation of processes including change and will focus on advanced monitoring and data analysis techniques. Interdisciplinarity will be sought by increased efforts to connect with the socio-economic sciences and geosciences in general. This paper presents a summary of the Science Plan of Panta Rhei, its targets, research questions and expected outcomes.

  • 207. Moseley, Christopher
    et al.
    Hohenegger, Cathy
    Berg, Peter
    SMHI, Research Department, Hydrology.
    Haerter, Jan O.
    Intensification of convective extremes driven by cloud-cloud interaction2016In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, no 10, p. 748-+Article in journal (Refereed)
  • 208. Musselman, Keith N.
    et al.
    Molotch, Noah P.
    Margulis, Steven A.
    Lehning, Michael
    Gustafsson, David
    SMHI, Research Department, Hydrology.
    Improved snowmelt simulations with a canopy model forced with photo-derived direct beam canopy transmissivity2012In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 48, article id W10509Article in journal (Refereed)
    Abstract [en]

    The predictive capacity of a physically based snow model to simulate point-scale, subcanopy snowmelt dynamics is evaluated in a mixed conifer forest, southern Sierra Nevada, California. Three model scenarios each providing varying levels of canopy structure detail were tested. Simulations of three water years initialized at locations of 24 ultrasonic snow depth sensors were evaluated against observations of snow water equivalent (SWE), snow disappearance date, and volumetric soil water content. When canopy model parameters canopy openness and effective leaf area index were obtained from satellite and literature-based sources, respectively, the model was unable to resolve the variable subcanopy snowmelt dynamics. When canopy parameters were obtained from hemispherical photos, the improvements were not statistically significant. However, when the model was modified to accept photo-derived time-varying direct beam canopy transmissivity, the error in the snow disappearance date was reduced by as much as one week and positive and negative biases in melt-season SWE and snow cover duration were significantly reduced. Errors in the timing of soil meltwater fluxes were reduced by 11 days on average. The optimum aggregated temporal model resolution of direct beam canopy transmissivity was determined to be 30 min; hourly averages performed no better than the bulk canopy scenarios and finer time steps did not increase overall model accuracy. The improvements illustrate the important contribution of direct shortwave radiation to subcanopy snowmelt and confirm the known nonlinear melt behavior of snow cover.

  • 209. Nijzink, R.C.
    et al.
    Almeida, S.
    Pechlivanidis, Ilias
    SMHI, Research Department, Hydrology.
    Capell, Réne
    SMHI, Research Department, Hydrology.
    Gustafsson, David
    SMHI, Research Department, Hydrology.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Parajka, J.
    Freer, J.
    Han, D.
    Wagener, T.
    van Nooijen, R.R.P.
    Savenije, H.H.G.
    Hrachowitz, M.
    Constraining Conceptual Hydrological ModelsWith Multiple Information Sources2018In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 54, no 10, p. 8332-8362Article in journal (Refereed)
    Abstract [en]

    The calibration of hydrological models without streamflow observations is problematic, and the simultaneous, combined use of remotely sensed products for this purpose has not been exhaustively tested thus far. Our hypothesis is that the combined use of products can (1) reduce the parameter search space and (2) improve the representation of internal model dynamics and hydrological signatures. Five different conceptual hydrological models were applied to 27 catchments across Europe. A parameter selection process, similar to a likelihood weighting procedure, was applied for 1,023 possible combinations of 10 different data sources, ranging from using 1 to all 10 of these products. Distances between the two empirical distributions of model performance metrics with and without using a specific product were determined to assess the added value of a specific product. In a similar way, the performance of the models to reproduce 27 hydrological signatures was evaluated relative to the unconstrained model. Significant reductions in the parameter space were obtained when combinations included Advanced Microwave Scanning Radiometer ‐ Earth Observing System and Advanced Scatterometer soil moisture, Gravity Recovery and Climate Experiment total water storage anomalies, and, in snow‐dominated catchments, the Moderate Resolution Imaging Spectroradiometer snow cover products. The evaporation products of Land Surface Analysis ‐ Satellite Application Facility and MOD16 were less effective for deriving meaningful, well‐constrained posterior parameter distributions. The hydrological signature analysis indicated that most models profited from constraining with an increasing number of data sources. Concluding, constraining models with multiple data sources simultaneously was shown to be valuable for at least four of the five hydrological models to determine model parameters in absence of streamflow.

  • 210. Nijzink, Remko
    et al.
    Hutton, Christopher
    Pechlivanidis, Ilias
    SMHI, Research Department, Hydrology.
    Capell, Réne
    SMHI, Research Department, Hydrology.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Freer, Jim
    Han, Dawei
    Wagener, Thorsten
    McGuire, Kevin
    Savenije, Hubert
    Hrachowitz, Markus
    The evolution of root-zone moisture capacities after deforestation: a step towards hydrological predictions under change?2016In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 20, no 12, p. 4775-4799Article in journal (Refereed)
    Abstract [en]

    The core component of many hydrological systems, the moisture storage capacity available to vegetation, is impossible to observe directly at the catchment scale and is typically treated as a calibration parameter or obtained from a priori available soil characteristics combined with estimates of rooting depth. Often this parameter is considered to remain constant in time. Using long-term data (30–40 years) from three experimental catchments that underwent significant land cover change, we tested the hypotheses that: (1) the root-zone storage capacity significantly changes after deforestation, (2) changes in the root-zone storage capacity can to a large extent explain post-treatment changes to the hydrological regimes and that (3) a time-dynamic formulation of the root-zone storage can improve the performance of a hydrological model.A recently introduced method to estimate catchment-scale root-zone storage capacities based on climate data (i.e. observed rainfall and an estimate of transpiration) was used to reproduce the temporal evolution of root-zone storage capacity under change. Briefly, the maximum deficit that arises from the difference between cumulative daily precipitation and transpiration can be considered as a proxy for root-zone storage capacity. This value was compared to the value obtained from four different conceptual hydrological models that were calibrated for consecutive 2-year windows.It was found that water-balance-derived root-zone storage capacities were similar to the values obtained from calibration of the hydrological models. A sharp decline in root-zone storage capacity was observed after deforestation, followed by a gradual recovery, for two of the three catchments. Trend analysis suggested hydrological recovery periods between 5 and 13 years after deforestation. In a proof-of-concept analysis, one of the hydrological models was adapted to allow dynamically changing root-zone storage capacities, following the observed changes due to deforestation. Although the overall performance of the modified model did not considerably change, in 51 % of all the evaluated hydrological signatures, considering all three catchments, improvements were observed when adding a time-variant representation of the root-zone storage to the model.In summary, it is shown that root-zone moisture storage capacities can be highly affected by deforestation and climatic influences and that a simple method exclusively based on climate data can not only provide robust, catchment-scale estimates of this critical parameter, but also reflect its time-dynamic behaviour after deforestation.

  • 211. 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.

  • 212. Olsson, Johanna Alkan
    et al.
    Jonsson, Anna C.
    Andersson, Lotta
    SMHI, Core Services.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    A model-supported participatory process for nutrient management: a socio-legal analysis of a bottom-up implementation of the EU Water Framework Directive2011In: International Journal of Agricultural Sustainability, ISSN 1473-5903, E-ISSN 1747-762X, Vol. 9, no 2, p. 379-389Article in journal (Refereed)
    Abstract [en]

    A methodology for local stakeholders' involvement in water management using a catchment model as a platform for dialogue has been developed and tested in the Kaggebo Bay drainage area in the southeast of Sweden. The process involved farmers, rural households not connected to municipal wastewater treatment facilities, local and regional authorities as well as different water and agricultural experts. This paper aims to assess whether and how the methodology has succeeded in encouraging social learning and promoting action and which barriers can be identified. The assessment shows that the methodology is able to create confidence in the process and increase the willingness to act as the methodology was able to adapt the form and content of the dialogue to better fit the cognitive and relational needs of involved stakeholders. It is also shown that the process may lead to a probable improvement of the eutrophication situation. However, if these types of processes are to serve not only as a basis for social learning and action at the local level, but also as the basis for a broader process of societal learning, then a mechanism to confer local ideas to the regional and national levels has to be clarified.

  • 213.
    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.

  • 214.
    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.

  • 215.
    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)
  • 216.
    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)
  • 217.
    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.

  • 218.
    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.

  • 219.
    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.

  • 220.
    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.

  • 221.
    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.

  • 222.
    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.

  • 223.
    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.

  • 224.
    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.

  • 225.
    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)
  • 226.
    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.

  • 227.
    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.

  • 228.
    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.

  • 229.
    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)
  • 230.
    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.

  • 231.
    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.

  • 232.
    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.

  • 233.
    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.

  • 234.
    Olsson, Jonas
    et al.
    SMHI, Research Department, Hydrology.
    Södling, Johan
    SMHI, Professional Services.
    Berg, Peter
    SMHI, Research Department, Hydrology.
    Wern, Lennart
    SMHI, Core Services.
    Eronn, Anna
    SMHI, Research Department, Climate research - Rossby Centre.
    Short-duration rainfall extremes in Sweden: a regional analysis2019In: Nordic Hydrology, ISSN 0029-1277, E-ISSN 1996-9694, Vol. 50, no 3, p. 945-960Article in journal (Refereed)
  • 235.
    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.

  • 236.
    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.

  • 237.
    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.

  • 238. Ouarda, T. B. M. J.
    et al.
    Charron, C.
    Hundecha, Yeshewatesfa
    SMHI, Research Department, Hydrology.
    St-Hilaire, A.
    Chebana, F.
    Introduction of the GAM model for regional low-flow frequency analysis at ungauged basins and comparison with commonly used approaches2018In: Environmental Modelling & Software, ISSN 1364-8152, E-ISSN 1873-6726, Vol. 109, p. 256-271Article in journal (Refereed)
  • 239. Parajka, Juraj
    et al.
    Bezak, Nejc
    Burkhart, John
    Hauksson, Bjarki
    Holko, Ladislav
    Hundecha, Yeshewatesfa
    SMHI, Research Department, Hydrology.
    Jenicek, Michal
    Krajci, Pavel
    Mangini, Walter
    Molnar, Peter
    Riboust, Philippe
    Rizzi, Jonathan
    Sensoy, Aynur
    Thirel, Guillaume
    Viglione, Alberto
    MODIS snowline elevation changes during snowmelt runoff events in Europe2019In: Journal of Hydrology and Hydromechanics, ISSN 0042-790X, E-ISSN 1338-4333, Vol. 67, no 1, p. 101-109Article in journal (Refereed)
  • 240. Parkes, B. L.
    et al.
    Wetterhall, Fredrik
    SMHI, Research Department, Hydrology.
    Pappenberger, F.
    He, Y.
    Malamud, B. D.
    Cloke, H. L.
    Assessment of a 1-hour gridded precipitation dataset to drive a hydrological model: a case study of the summer 2007 floods in the Upper Severn, UK2013In: HYDROLOGY RESEARCH, ISSN 1998-9563, Vol. 44, no 1, p. 89-105Article in journal (Refereed)
    Abstract [en]

    In this study a gridded hourly 1-km precipitation dataset for a meso-scale catchment (4,062 km(2)) of the Upper Severn River, UK was constructed using rainfall radar data to disaggregate a daily precipitation (rain gauge) dataset. The dataset was compared to an hourly precipitation dataset created entirely from rainfall radar data. Results found that when assessed against gauge readings and as input to the Lisflood-RR hydrological model, the rain gauge/radar disaggregated dataset performed the best suggesting that this simple method of combining rainfall radar data with rain gauge readings can provide temporally detailed precipitation datasets for calibrating hydrological models.

  • 241. Pechlivanidis, G. I.
    et al.
    Keramaris, E.
    Pechlivanidis, Ilias
    SMHI, Research Department, Hydrology.
    Samaras, G. A.
    Shear stress estimation in the linear zone over impermeable and permeable beds in open channels2015In: Desalination and Water Treatment, ISSN 1944-3994, E-ISSN 1944-3986, Vol. 54, no 8, p. 2181-2189Article in journal (Refereed)
    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.

  • 242.
    Pechlivanidis, Ilias
    et al.
    SMHI, Research Department, Hydrology.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Large-scale hydrological modelling by using modified PUB recommendations: the India-HYPE case2015In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 19, no 11, p. 4559-4579Article in journal (Refereed)
    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.

  • 243.
    Pechlivanidis, Ilias
    et al.
    SMHI, Research Department, Hydrology.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Donnelly, Chantal
    SMHI, Research Department, Hydrology.
    Hundecha, Yeshewatesfa
    SMHI, Research Department, Hydrology.
    Huang, S.
    Aich, V.
    Samaniego, L.
    Eisner, S.
    Shi, P.
    Analysis of hydrological extremes at different hydro-climatic regimes under present and future conditions2017In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 141, no 3, p. 467-481Article in journal (Refereed)
  • 244.
    Pechlivanidis, Ilias
    et al.
    SMHI, Research Department, Hydrology.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Donnelly, Chantal
    SMHI, Research Department, Hydrology.
    Hundecha, Yeshewatesfa
    SMHI, Research Department, Hydrology.
    Huang, S.
    Aich, V.
    Samaniego, L.
    Eisner, S.
    Shi, P.
    Analysis of hydrological extremes at different hydro-climatic regimes under present and future conditions.2016In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480Article in journal (Refereed)
  • 245. 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.

  • 246. 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.

  • 247.
    Pechlivanidis, Ilias
    et al.
    SMHI, Research Department, Hydrology.
    Gupta, H.
    Bosshard, Thomas
    SMHI, Research Department, Hydrology.
    An Information Theory Approach to Identifying a Representative Subset of Hydro-Climatic Simulations for Impact Modeling Studies2018In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 54, no 8, p. 5422-5435Article in journal (Refereed)
  • 248.
    Pechlivanidis, Ilias
    et al.
    SMHI, Research Department, Hydrology.
    Jackson, B.
    McMillan, H.
    Gupta, H.
    Use of an entropy-based metric in multiobjective calibration to improve model performance2014In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 50, no 10, p. 8066-8083Article in journal (Refereed)
    Abstract [en]

    Parameter estimation for hydrological models is complicated for many reasons, one of which is the arbitrary emphasis placed, by most traditional measures of fit, on various magnitudes of the model residuals. Recent research has called for the development of robust diagnostic measures that provide insights into which model structural components and/or data may be inadequate. In this regard, the flow duration curve (FDC) represents the historical variability of flow and is considered to be an informative signature of catchment behavior. Here we investigate the potential of using the recently developed conditioned entropy difference metric (CED) in combination with the Kling-Gupta efficiency (KGE). The CED respects the static information contained in the flow frequency distribution (and hence the FDC), but does not explicitly characterize temporal dynamics. The KGE reweights the importance of various hydrograph components (correlation, bias, variability) in a way that has been demonstrated to provide better model calibrations than the commonly used Nash-Sutcliffe efficiency, while being explicitly time sensitive. We employ both measures within a multiobjective calibration framework and achieve better performance over the full range of flows than obtained by single-criteria approaches, or by the common multiobjective approach that uses log-transformed and untransformed data to balance fitting of low and high flow periods. The investigation highlights the potential of CED to complement KGE (and vice versa) during model identification. It is possible that some of the complementarity is due to CED representing more information from moments >2 than KGE or other common metrics. We therefore suggest that an interesting way forward would be to extend KGE to include higher moments, i.e., use different moments as multiple criteria. Key Points <list id="wrcr21161-list-0001" list-type="bulleted"> <list-item id="wrcr21161-li-0001">CED provides an appropriate quantitative measure of fit to the FDC <list-item id="wrcr21161-li-0002">Complements between CED and KGE extracted flow information <list-item id="wrcr21161-li-0003">CED-KGE achieves better performance than single or common multiobjectives <doi origin="wiley" registered="yes">10.1002/(ISSN)1944-7973</doi

  • 249.
    Pechlivanidis, Ilias
    et al.
    SMHI, Research Department, Hydrology.
    Jackson, Bethanna
    Mcmillan, Hilary
    Gupta, Hoshin V.
    Robust informational entropy-based descriptors of flow in catchment hydrology2016In: Hydrological Sciences Journal, ISSN 0262-6667, E-ISSN 2150-3435, Vol. 61, no 1, p. 1-18Article in journal (Refereed)
    Abstract [en]

    This paper explores the use of entropy-based measures in catchment hydrology, and provides an importance-weighted numerical descriptor of the flow-duration curve. Although entropy theory is being applied in a wide spectrum of areas (including environmental and water resources), artefacts arising from the discrete, under-sampled and uncertain nature of hydrological data are rarely acknowledged, and have not been adequately explored. Here, we examine challenges to extracting hydrologically meaningful entropy measures from a flow signal; the effect of binning resolution on calculation of entropy is investigated, along with artefacts caused by (1) emphasis of information theoretic measures towards flow ranges having more data (statistically dominant information), and (2) effects of discharge measurement truncation errors. We introduce an importance-weighted entropy-based measure to counter the tendency of common binning approaches to over-emphasise information contained in the low flows which dominate the record. The measure uses a novel binning method, and overcomes artefacts due to data resolution and under-sampling. Our analysis reveals a fundamental problem with the extraction of information at high flows, due to the lack of statistically significant samples in this range. By separating the flow-duration curve into segments, our approach constrains the computed entropy to better respect distributional properties over the data range. When used as an objective function for model calibration, this approach constrains high flow predictions, as well as the commonly used Nash-Sutcliffe efficiency, but provides much better predictions of low flow behaviour.

  • 250.
    Pechlivanidis, Ilias
    et al.
    SMHI, Research Department, Hydrology.
    McIntyre, N.
    Wheater, H. S.
    The significance of spatial variability of rainfall on simulated runoff: an evaluation based on the Upper Lee catchment, UK2017In: Hydrology Research, ISSN 1998-9563, E-ISSN 2224-7955, Vol. 48, no 4, p. 1118-1130Article in journal (Refereed)
234567 201 - 250 of 332
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