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  • 1.
    Berggren, Karolina
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Olofsson, Mats
    Viklander, Maria
    Svensson, Gilbert
    Tools for measuring climate change impacts on urban drainage systems2007In: Techniques et stratégies durables pour la gestion des eaux urbaines par temps de pluie: NOVATECH 2007 ; 6e conférence internationale, juin 2007, Lyon, France, Villeurbanne: Graie , 2007, Vol. 1, p. 239-246Conference paper (Refereed)
  • 2.
    Berggren, Karolina
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Olofsson, Mats
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Svensson, Gilbert
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Gustafsson, Anna-Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Hydraulic impacts on urban drainage systems due to changes in rainfall, caused by climatic change2012In: Journal of hydrologic engineering, ISSN 1084-0699, E-ISSN 1943-5584, Vol. 17, no 1, p. 92-98Article in journal (Refereed)
    Abstract [en]

    The changes in climate were of a growing concern in the last decade, and will be even more so in the coming years. When investigating impacts on urban drainage systems due to changes in the climate, two challenges are (1) what type of input rainfall data to use, and (2) what parameters to measure the impacts. The overall objective of this study is to investigate the hydraulic performances ofurban drainage systems related to changes in rainfall, and through these hydraulic parameters describe impacts of climate change. Input rainfall data represents today's climate, as well as three future time periods (2011-2040, 2041-2070, and 2071-2100). The hydraulic parameters used were water levels in nodes (e.g. as the number of floods, frequency and duration of floods), and pipe flow ratio. For the study area, the number of flooded nodes and the geographical distribution of floods will increase in the future, as will both the flooding frequency and the duration of floods.

  • 3.
    Olofsson, Mats
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Climate change and urban drainage: future precipitation and hydraulic impact2007Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Increasing global mean temperature influences the hydrologic cycle. In the 21st century, hydrologic change featuring more heavy precipitation events is very likely according to the UN Intergovernmental Panel on Climate Change, IPCC. This change will have a great impact on urban environments and infrastructures. In Sweden, precipitation during the winter will most likely increase by as much as 30 to 50 % by the end of the 21st century, while summer precipitation will decrease in the southern and middle parts of Sweden. Recent years have seen a number of floods caused by heavy rainfalls. With climate change, the problem with floods can be expected to continue and increase. To prevent adverse damage, modelling how the changes in precipitation and temperature will influence the urban drainage systems and how measures can be taken to prevent or reduce the consequences of floods has become increasingly important. The main objective with this thesis is to investigate the hydraulic impact in an urban drainage system due to the presumed increase in intense rainfalls. Regional Climate models produce temperature and precipitation data for the future. The regional climate model RCA3 from Rossby Center at SMHI, produces data with a spatial resolution of 50*50 km and a temporal resolution of 30 min. To be able to use the climate data in urban drainage models, temporal and spatial resolution must be improved. A modification of the so-called Delta change method, where the changes are related to the rainfall intensity level, is presented to transfer the changes in rain characteristics from different future time periods to an observed series. For the study area, the climate model shows an increase of the highest intensities of up to 20 % for the 21st century. Effects of these changes are studied on an urban drainage system in the study area. Results from the urban drainage simulations show that higher water flow- ratios in pipes, longer durations of floods, and more frequent floods can be expected if the climate continues to change with more high intensity rains, as the climate models predict. The maximum water levels in nodes were significantly higher for all future time periods that were simulated. Even in the near future (2011-2040), maximum water levels in nodes were >0,1 m higher compared to today's climate. Since the renewal rate of pipes in the existing urban drainage system is relatively slow, emphasis must not lie only on city development but also on future climate change. Design criteria, therefore, need to be changed according to changes in precipitation. Weak spots in the system must be identified for the adaptation to be as effective as possible. Knowing when, where, and how to put the correct measures when adapting the urban drainage system is essential for efficient management. Climate change also affects urban drainage in different ways, depending on where in Sweden the city lies. In northern Sweden, problems can arise with changing snowmelt patterns, for example. Further research involves an analysis of the consequences that higher water levels, increased max flow, and higher seasonal variations will have and of the adaptation strategies required not only for the urban drainage systems but also for other infrastructures.

  • 4.
    Olofsson, Mats
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Olsson, Jonas
    SMHI.
    Berggren, Karolina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Viklander, Maria
    Adaptation of RCA3 climate model data for the specific needs of urban hydrology simulations2006In: Extreme Precipitation, Multisource Data Measurement and Uncertainty: Proceedings of the 7th International workshop on precipitation in urban areas / [ed] Peter Molnar, Zürich: Institute of Environmental Engineering, ETH, Zürich , 2006, p. 144-148Conference paper (Refereed)
    Abstract [en]

    Adapting climate model data to urban drainage applications can be done in several ways but a popular way is the so-called ‘delta change' 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 ‘delta factors' are related to the rainfall intensity level. This is achieved by calculating changes in the probability distribution of rainfall intensities and modelling the delta factors as a function of percentile. The model is applied to 30-min output from the RCA3 regional atmospheric climate model, in a grid box covering Kalmar City, Sweden. The climate model results indicate an increase of the highest intensities by up to ~20% and a decrease of lower intensities by up to almost 40%. This result is valid for a 30-min time scale, and to evaluate whether urban drainage impact assessment can be meaningfully performed on this time scale, a MOUSE model was applied in Kalmar using different time steps. The results indicate that a 30-min time step may be meaningful, but that ways to transfer the rainfall changes also to data of a higher time resolution needs to be considered. This will be done in future studies, as well as further testing and evaluation for other Swedish cities.

  • 5.
    Olofsson, Mats
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Östman, Anders
    University of Gävle, Gävle GIS Institute.
    Optimizing dynamic network configurations2006In: Proceedings of the 9th AGILE Conference on Geographic Information Science, 2006, p. 247-254Conference paper (Other academic)
  • 6.
    Olsson, J.
    et al.
    Research and Development (hydrology), Swedish Meteorological and Hydrological Institute, Norrköping.
    Berggren, Karolina
    Olofsson, Mats
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    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. 62, 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.

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