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  • 1. Aggarwal, Pradeep K.
    et al.
    Romatschke, Ulrike
    Araguas-Araguas, Luis
    Belachew, Dagnachew
    Longstaffe, Frederick J.
    Berg, Peter
    SMHI, Forskningsavdelningen, Hydrologi.
    Schumacher, Courtney
    Funk, Aaron
    Proportions of convective and stratiform precipitation revealed in water isotope ratios2016Ingår i: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, nr 8, s. 624-+Artikel i tidskrift (Refereegranskat)
  • 2.
    Berg, Peter
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Bosshard, Thomas
    SMHI, Forskningsavdelningen, Hydrologi.
    Yang, Wei
    SMHI, Forskningsavdelningen, Hydrologi.
    Model Consistent Pseudo-Observations of Precipitation and Their Use for Bias Correcting Regional Climate Models2015Ingår i: CLIMATE, ISSN 2225-1154, Vol. 3, nr 1, s. 118-132Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 3.
    Berg, Peter
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Christensen, Ole B.
    Klehmet, Katharina
    SMHI, Forskningsavdelningen, Hydrologi.
    Lenderink, Geert
    Olsson, Jonas
    SMHI, Forskningsavdelningen, Hydrologi.
    Teichmann, Claas
    Yang, Wei
    SMHI, Forskningsavdelningen, Hydrologi.
    Summertime precipitation extremes in a EURO-CORDEX 0.11 degrees ensemble at an hourly resolution2019Ingår i: Natural hazards and earth system sciences, ISSN 1561-8633, E-ISSN 1684-9981, Vol. 19, nr 4, s. 957-971Artikel i tidskrift (Refereegranskat)
  • 4.
    Berg, Peter
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Doescher, Ralf
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Koenigk, Torben
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Impacts of using spectral nudging on regional climate model RCA4 simulations of the Arctic2013Ingår i: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 6, nr 3, s. 849-859Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The performance of the Rossby Centre regional climate model RCA4 is investigated for the Arctic CORDEX (COordinated Regional climate Downscaling EXperiment) region, with an emphasis on its suitability to be coupled to a regional ocean and sea ice model. Large biases in mean sea level pressure (MSLP) are identified, with pronounced too-high pressure centred over the North Pole in summer of over 5 hPa, and too-low pressure in winter of a similar magnitude. These lead to biases in the surface winds, which will potentially lead to strong sea ice biases in a future coupled system. The large-scale circulation is believed to be the major reason for the biases, and an implementation of spectral nudging is applied to remedy the problems by constraining the large-scale components of the driving fields within the interior domain. It is found that the spectral nudging generally corrects for the MSLP and wind biases, while not significantly affecting other variables, such as surface radiative components, two-metre temperature and precipitation.

  • 5.
    Berg, Peter
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Doescher, Ralf
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Koenigk, Torben
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    On the effects of constraining atmospheric circulation in a coupled atmosphere-ocean Arctic regional climate model2016Ingår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 46, nr 11-12, s. 3499-3515Artikel i tidskrift (Refereegranskat)
  • 6.
    Berg, Peter
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Donnelly, Chantal
    SMHI, Forskningsavdelningen, Hydrologi.
    Gustafsson, David
    SMHI, Forskningsavdelningen, Hydrologi.
    Near-real-time adjusted reanalysis forcing data for hydrology2018Ingår i: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 22, nr 2, s. 989-1000Artikel i tidskrift (Refereegranskat)
  • 7.
    Berg, Peter
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Feldmann, H.
    Panitz, H. -J
    Bias correction of high resolution regional climate model data2012Ingår i: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 448, s. 80-92Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bias correction of varying complexity - from simple scaling and additive corrections to more advanced histogram equalisation (HE) corrections - is applied to high resolution (7 km) regional climate model (RCM) simulations. The aim of the study is to compare different methods that are easily implemented and applied to the data, and to assess the applicability and impact of the bias correction depending on the type of bias. The model bias is determined by comparison to a new gridded high resolution (1 km) data set of temperature and precipitation, which is also used as reference for the corrections. The performance of the different methods depends on the type of bias of the model, and on the investigated statistic. Whereas simpler methods correct the first moment of the distributions, they can have adverse effects on higher moments. The HE method corrects also higher moments, but approximations of the transfer function are necessary when applying the method to other data than the calibration data. Here, an empirical transfer function with linear fits to the tails is compared to a version where the complete function is approximated by a linear fit. The latter is thus limited to corrections of the first and second moments of the distribution. While making the transfer function more generally applicable, these approximations also limit the performance of the HE method. For the current model biases, the linear approximation is found suitable for precipitation, but for temperature it is not able to correct the whole distribution. The lower performance of the linear correction is most pronounced in summer, and is likely due to a difference in skewness between the model and observational data. Further limitations of the HE method are due to the need for long time series in order to have robust distributions for calculating the transfer function. Theoretical approximations of the required length of the calibration period were performed by using different sampling sizes drawn from a known distribution. The excerise show that about 30 year long time series are needed to have reasonable accuracy for the estimation of variance, when also corrections of the annual cycle is required. (C) 2012 Elsevier B.V. All rights reserved.

  • 8.
    Berg, Peter
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Moseley, Christopher
    Haerter, Jan O.
    Strong increase in convective precipitation in response to higher temperatures2013Ingår i: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 6, nr 3, s. 181-185Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Precipitation changes can affect society more directly than variations in most other meteorological observables(1-3), but precipitation is difficult to characterize because of fluctuations on nearly all temporal and spatial scales. In addition, the intensity of extreme precipitation rises markedly at higher temperature(4-9), faster than the rate of increase in the atmosphere's water-holding capacity(1,4), termed the Clausius-Clapeyron rate. Invigoration of convective precipitation (such as thunderstorms) has been favoured over a rise in strati-form precipitation (such as large-scale frontal precipitation) as a cause for this increase(4,10), but the relative contributions of these two types of precipitation have been difficult to disentangle. Here we combine large data sets from radar measurements and rain gauges over Germany with corresponding synoptic observations and temperature records, and separate convective and stratiform precipitation events by cloud observations. We find that for stratiform precipitation, extremes increase with temperature at approximately the Clausius-Clapeyron rate, without characteristic scales. In contrast, convective precipitation exhibits characteristic spatial and temporal scales, and its intensity in response to warming exceeds the Clausius-Clapeyron rate. We conclude that convective precipitation responds much more sensitively to temperature increases than stratiform precipitation, and increasingly dominates events of extreme precipitation.

  • 9.
    Berg, Peter
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Norin, Lars
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Olsson, Jonas
    SMHI, Forskningsavdelningen, Hydrologi.
    Creation of a high resolution precipitation data set by merging gridded gauge data and radar observations for Sweden2016Ingår i: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 541, s. 6-13Artikel i tidskrift (Refereegranskat)
  • 10.
    Berg, Peter
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Wagner, Sven
    Kunstmann, Harald
    Schaedler, Gerd
    High resolution regional climate model simulations for Germany: part I-validation2013Ingår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 40, nr 1-2, s. 401-414Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A five-member ensemble of regional climate model (RCM) simulations for Europe, with a high resolution nest over Germany, is analysed in a two-part paper: Part I (the current paper) presents the performance of the models for the control period, and Part II presents results for near future climate changes. Two different RCMs, CLM and WRF, were used to dynamically downscale simulations with the ECHAM5 and CCCma3 global climate models (GCMs), as well as the ERA40-reanalysis for validation purposes. Three realisations of ECHAM5 and one with CCCma3 were downscaled with CLM, and additionally one realisation of ECHAM5 with WRF. An approach of double nesting was used, first to an approximately 50 km resolution for entire Europe and then to a domain of approximately 7 km covering Germany and its near surroundings. Comparisons of the fine nest simulations are made to earlier high resolution simulations for the region with the RCM REMO for two ECHAM5 realisations. Biases from the GCMs are generally carried over to the RCMs, which can then reduce or worsen the biases. The bias of the coarse nest is carried over to the fine nest but does not change in amplitude, i.e. the fine nest does not add additional mean bias to the simulations. The spatial pattern of the wet bias over central Europe is similar for all CLM simulations, and leads to a stronger bias in the fine nest simulations compared to that of WRF and REMO. The wet bias in the CLM model is found to be due to a too frequent drizzle, but for higher intensities the distributions are well simulated with both CLM and WRF at the 50 and 7 km resolutions. Also the spatial distributions are close to high resolution gridded observations. The REMO model has low biases in the domain averages over Germany and no drizzle problem, but has a shift in the mean precipitation patterns and a strong overestimation of higher intensities. The GCMs perform well in simulating the intensity distribution of precipitation at their own resolution, but the RCMs add value to the distributions when compared to observations at the fine nest resolution.

  • 11. Eggert, B.
    et al.
    Berg, Peter
    SMHI, Forskningsavdelningen, Hydrologi.
    Haerter, J. O.
    Jacob, D.
    Moseley, C.
    Temporal and spatial scaling impacts on extreme precipitation2015Ingår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 15, nr 10, s. 5957-5971Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Convective and stratiform precipitation events have fundamentally different physical causes. Using a radar composite over Germany, this study separates these precipitation types and compares extremes at different spatial and temporal scales, ranging from 1 to 50 km and 5 min to 6 h, respectively. Four main objectives are addressed. First, we investigate extreme precipitation intensities for convective and stratiform precipitation events at different spatial and temporal resolutions to identify type-dependent space and time reduction factors and to analyze regional and seasonal differences over Germany. We find strong differences between the types, with up to 30% higher reduction factors for convective compared to stratiform extremes, exceeding all other observed seasonal and regional differences within one type. Second, we investigate how the differences in reduction factors affect the contribution of each type to extreme events as a whole, again dependent on the scale and the threshold chosen. A clear shift occurs towards more convective extremes at higher resolution or higher percentiles. For horizontal resolutions of current climate model simulations, i.e., similar to 10 km, the temporal resolution of the data as well as the chosen threshold have profound influence on which type of extreme will be statistically dominant. Third, we compare the ratio of area to duration reduction factor for convective and stratiform events and find that convective events have lower effective advection velocities than stratiform events and are therefore more strongly affected by spatial than by temporal aggregation. Finally, we discuss the entire precipitation distribution regarding data aggregation and identify matching pairs of temporal and spatial resolutions where similar distributions are observed. The information is useful for planning observational networks or storing model data at different temporal and spatial scales.

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

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

  • 13. Fosser, G.
    et al.
    Khodayar, S.
    Berg, Peter
    SMHI, Forskningsavdelningen, Hydrologi.
    Climate change in the next 30 years: What can a convection-permitting model tell us that we did not already know?2017Ingår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 48, nr 5-6, s. 1987-2003Artikel i tidskrift (Refereegranskat)
  • 14. Haerter, Jan O.
    et al.
    Berg, Peter
    SMHI, Forskningsavdelningen, Hydrologi.
    Moseley, Christopher
    Precipitation onset as the temporal reference in convective self-organization2017Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, nr 12, s. 6450-6459Artikel i tidskrift (Refereegranskat)
  • 15. Haerter, Jan O.
    et al.
    Eggert, Bastian
    Moseley, Christopher
    Piani, Claudio
    Berg, Peter
    SMHI, Forskningsavdelningen, Hydrologi.
    Statistical precipitation bias correction of gridded model data using point measurements2015Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, nr 6, s. 1919-1929Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is well known that climate model output data cannot be used directly as input to impact models, e.g., hydrology models, due to climate model errors. Recently, it has become customary to apply statistical bias correction to achieve better statistical correspondence to observational data. As climate model output should be interpreted as the space-time average over a given model grid box and output time step, the status quo in bias correction is to employ matching gridded observational data to yield optimal results. Here we show that when gridded observational data are not available, statistical bias correction can be carried out using point measurements, e.g., rain gauges. Our nonparametric method, which we call scale-adapted statistical bias correction (SABC), is achieved by data aggregation of either the available modeled or gauge data. SABC is a straightforward application of the well-known Taylor hypothesis of frozen turbulence. Using climate model and rain gauge data, we show that SABC performs significantly better than equal-time period statistical bias correction.

  • 16.
    Koenigk, Torben
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Berg, Peter
    SMHI, Forskningsavdelningen, Hydrologi.
    Doescher, Ralf
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Arctic climate change in an ensemble of regional CORDEX simulations2015Ingår i: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 34, artikel-id 24603Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 17.
    Lucas-Picher, Philippe
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Boberg, Fredrik
    Christensen, Jens H.
    Berg, Peter
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Dynamical Downscaling with Reinitializations: A Method to Generate Finescale Climate Datasets Suitable for Impact Studies2013Ingår i: Journal of Hydrometeorology, ISSN 1525-755X, E-ISSN 1525-7541, Vol. 14, nr 4, s. 1159-1174Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To retain the sequence of events of a regional climate model (RCM) simulation driven by a reanalysis, a method that has not been widely adopted uses an RCM with frequent reinitializations toward its driving field. In this regard, this study highlights the benefits of an RCM simulation with frequent (daily) reinitializations compared to a standard continuous RCM simulation. Both simulations are carried out with the RCM HIRHAM5, driven with the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) data, over the 12-km-resolution European Coordinated Regional Climate Downscaling Experiment (CORDEX) domain covering the period 1989-2009. The analysis of daily precipitation shows improvements in the sequence of events and the maintenance of the added value from the standard continuous RCM simulation. The validation of the two RCM simulations with observations reveals that the simulation with reinitializations indeed improves the temporal correlation. Furthermore, the RCM simulation with reinitializations has lower systematic errors compared to the continuous simulation, which has a tendency to be too wet. A comparison of the distribution of wet day precipitation intensities shows similar added value in the continuous and reinitialized simulations with higher variability and extremes compared to the driving field ERA-Interim. Overall, the results suggest that the finescale climate dataset of the RCM simulation with reinitializations better suits the needs of impact studies by providing a sequence of events matching closely the observations, while limiting systematic errors and generating reliable added value. Downsides of the method with reinitializations are increased computational costs and the introduction of temporal discontinuities that are similar to those of a reanalysis.

  • 18. Moseley, Christopher
    et al.
    Berg, Peter
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Haerter, Jan O.
    Probing the precipitation life cycle by iterative rain cell tracking2013Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 118, nr 24, s. 13361-13370Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Monitoring the life cycle of convective rain cells requires a Lagrangian viewpoint where the observer moves with the dominant background flow. To adopt such a moving reference frame, we design, validate, and apply a simple rain cell tracking methodwhich we term iterative rain cell tracking (IRT)for spatio-temporal precipitation data. IRT iteratively identifies the formation and dissipation of rain cells and determines the large-scale flow. The iteration is repeated until reaching convergence. As validated using reanalysis wind speeds, repeated iterations lead to substantially increased agreement of the background flow field and an increased number of complete tracks. Our method is thereby able to monitor the growth and intensity profiles of rain cells and is applied to a high-resolution (5 min and 1x1 km(2)) data set of radar-derived rainfall intensities over Germany. We then combine this data set with surface temperature observations and synoptic observations to group tracks according to convective and stratiform conditions. Convective tracks show clear life cycles in intensity, with peaks shifted off-center toward the beginning of the track, whereas stratiform tracks have comparatively featureless intensity profiles. Our results show that the convective life cycle can lead to convection-dominating precipitation extremes at short time scales, while track-mean intensities may vary much less between the two types. The observed features become more pronounced as surface temperature increases, and in the case of convection even exceeded the rates expected from the Clausius-Clapeyron relation.

  • 19. Moseley, Christopher
    et al.
    Hohenegger, Cathy
    Berg, Peter
    SMHI, Forskningsavdelningen, Hydrologi.
    Haerter, Jan O.
    Intensification of convective extremes driven by cloud-cloud interaction2016Ingår i: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, nr 10, s. 748-+Artikel i tidskrift (Refereegranskat)
  • 20.
    Olsson, Jonas
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Berg, Peter
    SMHI, Forskningsavdelningen, Hydrologi.
    Eronn, Anna
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Simonsson, Lennart
    SMHI, Forskningsavdelningen, Hydrologi.
    Södling, Johan
    SMHI, Affärsverksamhet.
    Wern, Lennart
    SMHI, Samhälle och säkerhet.
    Yang, Wei
    SMHI, Forskningsavdelningen, Hydrologi.
    Extremregn i nuvarande och framtida klimat Analyser av observationer och framtidsscenarier2018Rapport (Övrigt vetenskapligt)
    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, Forskningsavdelningen, Hydrologi.
    Berg, Peter
    SMHI, Forskningsavdelningen, Hydrologi.
    Kawamura, Akira
    Impact of RCM Spatial Resolution on the Reproduction of Local, Subdaily Precipitation2015Ingår i: Journal of Hydrometeorology, ISSN 1525-755X, E-ISSN 1525-7541, Vol. 16, nr 2, s. 534-547Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 22.
    Olsson, Jonas
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Södling, Johan
    SMHI, Affärsverksamhet.
    Berg, Peter
    SMHI, Forskningsavdelningen, Hydrologi.
    Wern, Lennart
    SMHI, Samhälle och säkerhet.
    Eronn, Anna
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Short-duration rainfall extremes in Sweden: a regional analysis2019Ingår i: Nordic Hydrology, ISSN 0029-1277, E-ISSN 1996-9694, Vol. 50, nr 3, s. 945-960Artikel i tidskrift (Refereegranskat)
  • 23. Ott, Irena
    et al.
    Duethmann, Doris
    Liebert, Joachim
    Berg, Peter
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Feldmann, Hendrik
    Ihringer, Juergen
    Kunstmann, Harald
    Merz, Bruno
    Schaedler, Gerd
    Wagner, Sven
    High-Resolution Climate Change Impact Analysis on Medium-Sized River Catchments in Germany: An Ensemble Assessment2013Ingår i: Journal of Hydrometeorology, ISSN 1525-755X, E-ISSN 1525-7541, Vol. 14, nr 4, s. 1175-1193Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The impact of climate change on three small- to medium-sized river catchments (Ammer, Mulde, and Ruhr) in Germany is investigated for the near future (2021-50) following the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A1B scenario. A 10-member ensemble of hydrological model (HM) simulations, based on two high-resolution regional climate models (RCMs) driven by two global climate models (GCMs), with three realizations of ECHAM5 (E5) and one realization of the Canadian Centre for Climate Modelling and Analysis version 3 (CCCma3; C3) is established. All GCM simulations are downscaled by the RCM Community Land Model (CLM), and one realization of E5 is downscaled also with the RCM Weather Research and Forecasting Model (WRF). This concerted 7-km, high-resolution RCM ensemble provides a sound basis for runoff simulations of small catchments and is currently unique for Germany. The hydrology for each catchment is simulated in an overlapping scheme, with two of the three HMs used in the project. The resulting ensemble hence contains for each chain link (GCM-realization-RCM-HM) at least two members and allows the investigation of qualitative and limited quantitative indications of the existence and uncertainty range of the change signal. The ensemble spread in the climate change signal is large and varies with catchment and season, and the results show that most of the uncertainty of the change signal arises from the natural variability in winter and from the RCMs in summer.

  • 24.
    Persson, Gunn
    et al.
    SMHI, Affärsverksamhet.
    Nylén, Linda
    SMHI, Affärsverksamhet.
    Berggreen-Clausen, Steve
    SMHI, Affärsverksamhet.
    Berg, Peter
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Rayner, David
    SMHI.
    Sjökvist, Elin
    SMHI, Affärsverksamhet.
    Från utsläppsscenarier till lokal nederbörd och översvämningsrisker2016Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Inom det av MSB finansierade projektet ”Nederbörd och översvämningar i ramtidens Sverige - ett system till stöd för klimatanpassning” har SMHI ansvarat för hydrologisk och hydraulisk modellering samt framtagande av tidsserier med lokalt klimat för framtida förhållanden. Två metoder att bearbeta klimatdata har använts; SMHI:s Distributionsbaserad skalering (DBS) och en statistisk metod utarbetad vid Göteborgs universitet.

  • 25.
    Persson, Gunn
    et al.
    SMHI, Affärsverksamhet.
    Strandberg, Gustav
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Berg, Peter
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Vägledning för användande av klimatscenarier2015Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    SMHI fick i sitt regleringsbrev för år 2014 uppdraget att, i samråd med berörda myndigheter och andra aktörer, ta fram en vägledning för användandet av klimatscenarier. Enligt önskemål framtogs vägledningen som en webb-produkt på smhi.se, i anslutning till klimatscenarier. Materialet finns även samlat i denna rapport, såsom det lanserades hösten 2014. Eftersom materialet är uppbyggt för webb-presentation, där läsaren ska kunna gå in i kapitel utan att ha läst de tidigare, förekommer en del upprepningar. Klimatscenarier är beskrivningar av hur klimatet kan utvecklas i framtiden. Vägledningen ger stöd för att tolka och använda klimatscenarier, med dess möjligheter och begränsningar. Klimateffektstudier beskrivs översiktligt och med fokus på hydrologiska effektstudier. Några enkla steg för att komma igång med klimatanpassning presenteras också. I ordlistan förklaras de begrepp som används.

  • 26. Westra, S.
    et al.
    Fowler, H. J.
    Evans, J. P.
    Alexander, L. V.
    Berg, Peter
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Johnson, F.
    Kendon, E. J.
    Lenderink, G.
    Roberts, N. M.
    Future changes to the intensity and frequency of short-duration extreme rainfall2014Ingår i: Reviews of geophysics, ISSN 8755-1209, E-ISSN 1944-9208, Vol. 52, nr 3, s. 522-555Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Evidence that extreme rainfall intensity is increasing at the global scale has strengthened considerably in recent years. Research now indicates that the greatest increases are likely to occur in short-duration storms lasting less than a day, potentially leading to an increase in the magnitude and frequency of flash floods. This review examines the evidence for subdaily extreme rainfall intensification due to anthropogenic climate change and describes our current physical understanding of the association between subdaily extreme rainfall intensity and atmospheric temperature. We also examine the nature, quality, and quantity of information needed to allow society to adapt successfully to predicted future changes, and discuss the roles of observational and modeling studies in helping us to better understand the physical processes that can influence subdaily extreme rainfall characteristics. We conclude by describing the types of research required to produce a more thorough understanding of the relationships between local-scale thermodynamic effects, large-scale atmospheric circulation, and subdaily extreme rainfall intensity.

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