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Modelling, mapping and visualisation of flood inundation uncertainties
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management, Land management, GIS.ORCID iD: 0000-0002-3906-6088
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Flood maps showing extents of predicted flooding for a given extreme event have wide usage in all types of spatial planning tasks, as well as serving as information material for the public. However, the production processes that these maps undergo (including the different data, methods, models and decisions from the persons generating them), which include both Geographic Information Systems (GIS) and hydraulic modelling, affect the map’s content, and will be reflected in the final map. A crisp flood boundary, which is a common way of representing the boundary in flood maps, may therefore not be the best representation to be used. They provide a false implication that these maps are correct and that the flood extents are absolute, despite the effects of the entire modelling in the prediction output. Hence, this research attempts to determine how flood prediction outputs can be affected by uncertainties in the modelling process. In addition, it tries to evaluate how users understand, utilise and perceive flood uncertainty information. 

Three main methods were employed in the entire research: uncertainty modelling and analyses; map and geovisualisation development; and user assessment. The studies in this work showed that flood extents produced were influenced by the Digital Elevation Model (DEM) resolution and the Manning’s  used. This effect was further increased by the topographic characteristic of the floodplain. However, the performance measure used, which quantify how well a model produces result in relation to a reference floor boundary, had also biases in quantifying outputs. Determining the optimal model output, therefore, depended on outcomes of the goodness-of-fit measures used.

 In this research, several ways were suggested on how uncertainties can be visualised based on the data derived from the uncertainty assessment and by characterising the uncertainty information. These can be through: dual-ended maps; flood probability maps; sequential maps either highlighting the degrees of certainty (certainty map) or degrees of uncertainty (uncertainty map) in the data; binary maps; overlain flood boundaries from different calibration results; and performance bars. Different mapping techniques and visual variables were used for their representation. These mapping techniques employed, as well as the design of graphical representation, helped facilitate understanding the information by the users, especially when tested during the evaluations. Note though that there were visualisations, which the user found easier to comprehend depending on the task given. Each of these visualisations had also its advantages and disadvantages in communicating flood uncertainty information, as shown in the assessments conducted. Another important aspect that came out in the study was how the users’ background influence decision-making when using these maps. Users’ willingness to take risks depended not only on the map, but their perceptions on the risk itself. However, overall, users found the uncertainty maps to be useful to be incorporated in planning tasks.

Abstract [sv]

Översvämningskartor som visar utbredningen av förutspådda översvämningar för vissa extrema händelser har stor användning i all typ av samhällsplanering, samt fungerar som informationsmaterial för allmänheten. Men, de produktionsprocesser som dessa kartor genomgår (inkluderande olika data, metoder, modeller och beslut från de personer som genererar dessa) och som innefattar både geografiska informationssystem (GIS) och hydraulisk modellering, påverkar kartornas innehåll, vilket även återspeglas i de slutliga kartornas utseende. En skarp översvämningsgräns, som är det vanliga sättet att visa gränsen i översvämningskartor, är därför antagligen inte det bästa sättet att representera utbredningen. Sådana gränser ger en falsk trygghet i att dessa kartor är korrekta och att översvämningsutbredningen är absolut, trots att hela processen att producera dem innebär osäkerheter. Denna studie försöker därför undersöka hur översvämningskartering påverkas av osäkerheter i modelleringsprocesser och hur dessa osäkerheter kan representeras, visualiseras och kommuniceras i kartorna. Dessutom försöker studien utvärdera hur olika användare förstår, använder och uppfattar översvämningskartor som innehåller osäkerhetsinformation.

Tre huvudmetoder har använts i denna studie: osäkerhetsmodellering och analys, kart- och geovisualiseringsutveckling samt användarstudier. Resultaten visar att översvämningsgränserna påverkades både av de digitala höjdmodellernas upplösning (cellstorlek) och markens friktion, representerat av Mannings 𝑛, men också av markens topografi. För att kvantifiera skillnaderna mellan modell och referensöversvämningsyta och därefter kunna välja den mest optimala modellen användes olika valideringsmetoder. Dessa lider dock också av olika brister, vilket gör att resultaten varierar beroende på den valideringsmetod som används.

I denna studie föreslås flera sätt att visualisera osäkerheter baserat på resultaten från osäkerhetsmodellering och karaktären av osäkerhetsinformation. Dessa utgörs av kartor med divergerande färgramp (sk. dual-ended colour maps), sekventiella kartor (som framhäver graden av säkerhet, respektive osäkerhet), binära kartor, överlagring av översvämningsgränser från olika modeller samt värdestaplar. Olika karteringsmetoder och visuella variabler användes för att representera informationen. Resultat från en användarstudie visade att dessa, samt utformningen av den grafiska representationen, underlättade förståelsen av informationen. Beroende på uppgiften finns det visualisering som är lättare eller svårare att förstå för kartanvändarna. Varje visualisering hade också för- och nackdelar med att kommunicera översvämningsosäkerhetsinformation. En annan viktig aspekt som kom fram i studien var hur användarnas bakgrund påverkar beslutsfattandet när de använde de olika kartorna. Användarnas vilja att ta risker berodde inte bara på kartan, utan också på deras uppfattning av risken i sig. Sammantaget visade det sig emellertid att osäkerhetskartorna är användbara för planeringsuppgifter.

Place, publisher, year, edition, pages
Gävle: Gävle University Press , 2018. , p. 109
Series
Studies in the Research Profile Built Environment. Doctoral thesis ; 10
Keywords [en]
cartography, flood, hydraulic modelling, GIS, map, uncertainty, visualisation
Keywords [sv]
GIS, hydraulisk modellering, karta, kartografi, osäkerhet, visualisering, översvämning
National Category
Computer and Information Sciences Other Earth and Related Environmental Sciences Civil Engineering
Identifiers
URN: urn:nbn:se:hig:diva-27995ISBN: 978-91-88145-33-8 (print)ISBN: 978-91-88145-34-5 (electronic)OAI: oai:DiVA.org:hig-27995DiVA, id: diva2:1254912
Public defence
2018-12-10, Lilla Jadwigasalen (12:108), Kungsbäcksvägen 47, Gävle, 15:00 (English)
Opponent
Supervisors
Available from: 2018-11-13 Created: 2018-10-10 Last updated: 2018-11-13
List of papers
1. Importance of river bank and floodplain slopes on the accuracy of flood inundation mapping
Open this publication in new window or tab >>Importance of river bank and floodplain slopes on the accuracy of flood inundation mapping
2012 (English)In: River Flow 2012: Volume 2 / [ed] Rafael Murillo Muñoz, Leiden, The Netherlands: CRC Press / Balkema (Taylor & Francis) , 2012, p. 1015-1020Conference paper, Published paper (Refereed)
Abstract [en]

Effective flood assessment and management depend on accurate models of flood events, which in turn are strongly affected by the quality of digital elevation models (DEMs). In this study, HEC-RAS was used to route one specificwater discharge through the main channel of the Eskilstuna River, Sweden. DEMs with various resolutions and accuracies were used to model the inundation. The results showed a strong positive relationship between the quality of theDEMand the extent of the inundation. However, evenDEMswith the highest resolution produced inaccuracies. In another case study, the Testebo River, the model settings could be calibrated, thanks to a surveyed old inundation event. However, even with the calibration efforts, the resulting inundation extents showed varying degrees of deviation from the surveyed flood boundaries. Therefore, it becomes clear that not only does the resolution of the DEM impact the quality of the results; also, the floodplain slope perpendicular to the river flow will impact the modelling accuracy. Flatter areas exhibited the greatest predictive uncertainties regardless of the DEM’s resolution. For perfectly flat areas, uncertainty becomes infinite.

Place, publisher, year, edition, pages
Leiden, The Netherlands: CRC Press / Balkema (Taylor & Francis), 2012
Keywords
Flood Inundation, Geographical Information Systems (GIS), LiDAR, Digital Elevation Models (DEM)
National Category
Other Civil Engineering Ocean and River Engineering Remote Sensing Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:hig:diva-12942 (URN)000347871500135 ()2-s2.0-84867959207 (Scopus ID)978-0-415-62129-8 (ISBN)978-0-203-07635-4 (ISBN)978-1-4665-7552-3 (ISBN)
Conference
International Conference on Fluvial Hydraulics. River Flow 2012. San José, Costa Rica, 5-7 September 2012
Projects
DaGIS, GLOBESKvalitetsbeskrivning av geografisk information vid översvämningskartering
Note

Partly financed by the European Union through Swedish Agency for Economic and Regional Growth (Tillväxtverket) (project number 151092).

Available from: 2012-09-18 Created: 2012-09-18 Last updated: 2018-10-10Bibliographically approved
2. Geovisualisation of uncertainty in simulated flood maps
Open this publication in new window or tab >>Geovisualisation of uncertainty in simulated flood maps
2014 (English)In: Proceedings of the International Conferences on Interfaces and Human Computer Interaction 2014, Game and Entertainment Technologies 2014 and Computer Graphics, Visualization, Computer Vision and Image Processing 2014 - Part of the Multi Conference on Computer Science and Information Systems, MCCSIS 2014 / [ed] Katherine Blashki and Yingcai Xiao, IADIS Press , 2014, p. 206-214Conference paper, Published paper (Refereed)
Abstract [en]

The paper presents a three-dimensional (3D) geovisualisation model of uncertainties in simulated flood maps that can help communicate uncertain information in the data being used. An entropy-based measure was employed for uncertainty quantification. In developing the model, Visualisation Toolkit (VTK) was utilised. Different data derived from earlier simulation study and other maps were represented in the model. Cartographic principles were considered in the map design. A Graphical User Interface (GUI), which was developed in Tkinter, was also created to further support exploratory data analysis. The resulting model allowed visual identification of uncertain areas, as well as displaying spatial relationship between the entropy and the slope values. This geovisualisation has still to be tested to assess its effectiveness as a communication tool. However, this type of uncertainty visualisation in flood mapping is an initial step that can lead to its adoption in decision-making when presented comprehensively to its users. Thus, further improvement and development is still suggested for this kind of information presentation.

Place, publisher, year, edition, pages
IADIS Press, 2014
Keywords
Flood, entropy, exploratory analysis, geovisualisation, uncertainty analysis
National Category
Other Computer and Information Science
Identifiers
urn:nbn:se:hig:diva-17659 (URN)2-s2.0-84929408117 (Scopus ID)
Conference
8th Multi Conference on Computer Science and Information Systems (MCCSIS), Lisbon, Portugal, 15-19 July 2014
Available from: 2014-10-09 Created: 2014-10-09 Last updated: 2018-12-03Bibliographically approved
3. Visualisation and evaluation of flood uncertainties based on ensemble modelling
Open this publication in new window or tab >>Visualisation and evaluation of flood uncertainties based on ensemble modelling
2016 (English)In: International Journal of Geographical Information Science, ISSN 1365-8816, E-ISSN 1365-8824, Vol. 30, no 2, p. 240-262Article in journal (Refereed) Published
Abstract [en]

This study evaluates how users incorporate visualisation of flood uncertainty information in decision-making. An experiment was conducted where participants were given the task to decide building locations, taking into account homeowners’ preferences as well as dilemmas imposed by flood risks at the site. Two general types of visualisations for presenting uncertainties from ensemble modelling were evaluated: (1) uncertainty maps, which used aggregated ensemble results; and (2) performance bars showing all individual simulation outputs from the ensemble. Both were supplemented with either two-dimensional (2D) or three-dimensional (3D) contextual information, to give an overview of the area.The results showed that the type of uncertainty visualisation was highly influential on users’ decisions, whereas the representation of the contextual information (2D or 3D) was not. Visualisation with performance bars was more intuitive and effective for the task performed than the uncertainty map. It clearly affected users’ decisions in avoiding certain-to-be-flooded areas. Patterns to which the distances were decided from the homeowners’ preferred positions and the uncertainties were similar, when the 2D and 3D map models were used side by side with the uncertainty map. On the other hand, contextual information affected the time to solve the task. With the 3D map, it took the participants longer time to decide the locations, compared with the other combinations using the 2D model.Designing the visualisation so as to provide more detailed information made respondents avoid dangerous decisions. This has also led to less variation in their overall responses.

Place, publisher, year, edition, pages
Taylor & Francis, 2016
Keywords
visualisation, uncertainty, flood, ensemble modelling, decision-making
National Category
Computer and Information Sciences Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:hig:diva-20124 (URN)10.1080/13658816.2015.1085539 (DOI)000365550900006 ()2-s2.0-84948086666 (Scopus ID)
Note

Finasierat via European Union (EU) through Tillvaxtverket [GLOBES 2 project] projektnummer: 170430

Available from: 2015-08-19 Created: 2015-08-19 Last updated: 2018-12-03Bibliographically approved
4. Visualising DEM-related flood-map uncertainties using a disparity-distance equation algorithm
Open this publication in new window or tab >>Visualising DEM-related flood-map uncertainties using a disparity-distance equation algorithm
2016 (English)In: IAHS-AISH Proceedings and Reports / [ed] A. H. Schumann, G. Blöschl, A. Castellarin, J. Dietrich, S. Grimaldi, U. Haberlandt, A. Montanari, D. Rosbjerg, A. Viglione, and S. Vorogushyn, Göttingen: Copernicus Publications on behalf of International Association of Hydrological Sciences (IAHS) , 2016, Vol. 373, p. 153-159Conference paper, Published paper (Refereed)
Abstract [en]

The apparent absoluteness of information presented by crisp-delineated flood boundaries can lead tomisconceptions among planners about the inherent uncertainties associated in generated flood maps. Even mapsbased on hydraulic modelling using the highest-resolution digital elevation models (DEMs), and calibrated withthe most optimal Manning’s roughness (n) coefficients, are susceptible to errors when compared to actual floodboundaries, specifically in flat areas. Therefore, the inaccuracies in inundation extents, brought about by thecharacteristics of the slope perpendicular to the flow direction of the river, have to be accounted for. Instead ofusing the typical Monte Carlo simulation and probabilistic methods for uncertainty quantification, an empiricalbaseddisparity-distance equation that considers the effects of both the DEM resolution and slope was used tocreate prediction-uncertainty zones around the resulting inundation extents of a one-dimensional (1-D) hydraulicmodel. The equation was originally derived for the Eskilstuna River where flood maps, based on DEM dataof different resolutions, were evaluated for the slope-disparity relationship. To assess whether the equation isapplicable to another river with different characteristics, modelled inundation extents from the Testebo Riverwere utilised and tested with the equation. By using the cross-sectional locations, water surface elevations, andDEM, uncertainty zones around the original inundation boundary line can be produced for different confidences.The results show that (1) the proposed method is useful both for estimating and directly visualising modelinaccuracies caused by the combined effects of slope and DEM resolution, and (2) the DEM-related uncertaintiesalone do not account for the total inaccuracy of the derived flood map. Decision-makers can apply it to alreadyexisting flood maps, thereby recapitulating and re-analysing the inundation boundaries and the areas that areuncertain. Hence, more comprehensive flood information can be provided when determining locations whereextra precautions are needed. Yet, when applied, users must also be aware that there are other factors that caninfluence the extent of the delineated flood boundary.

Place, publisher, year, edition, pages
Göttingen: Copernicus Publications on behalf of International Association of Hydrological Sciences (IAHS), 2016
Series
IAHS-AISH Proceedings and Reports, ISSN 01447815 ; 373
Keywords
River floods, Hydraulic modelling, Inundation mapping, Digital elevation models (DEM), Uncertainty
National Category
Ocean and River Engineering Oceanography, Hydrology and Water Resources Physical Geography Remote Sensing
Identifiers
urn:nbn:se:hig:diva-21496 (URN)10.5194/piahs-373-153-2016 (DOI)000391006000026 ()2-s2.0-85044511792 (Scopus ID)
Conference
7th International Water Resources Management Conference of ICWRS, 18-20 May 2016, ochum, Germany
Available from: 2016-05-13 Created: 2016-05-13 Last updated: 2018-10-10Bibliographically approved
5. Color map design for visualization in flood risk assessment
Open this publication in new window or tab >>Color map design for visualization in flood risk assessment
2017 (English)In: International Journal of Geographical Information Science, ISSN 1365-8816, E-ISSN 1365-8824, Vol. 31, no 11, p. 2286-2309Article in journal (Refereed) Published
Abstract [en]

Visualizations of flood maps from simulation models are widely used for assessing the likelihood of flood hazards in spatial planning. The choice of a suitable type of visualization as well as efficient color maps is critical to avoid errors or bias when interpreting the data. Based on a review of previous flood uncertainty visualization techniques, this paper identifies areas of improvements and suggests criteria for the design of a task-specific color scale in flood map visualization. We contribute a novel color map design for visualizing probabilities and uncertainties from flood simulation ensembles. A user study encompassing 83 participants was carried out to evaluate the effects of this new color map on user’s decisions in a spatial planning task. We found that the type of visualization makes a difference when it comes to identification of non-hazardous sites in the flood risk map and when accepting risks in more uncertain areas. In comparison with two other existing visualization techniques, we observed that the new design was superior both in terms of task compliance and efficiency. In regions with uncertain flood statuses, users were biased toward accepting less risky locations with our new color map design.

Keywords
color scales, ensemble modeling, flood maps, user study, Visualization
National Category
Physical Geography Other Computer and Information Science
Identifiers
urn:nbn:se:hig:diva-24871 (URN)10.1080/13658816.2017.1349318 (DOI)000408205100009 ()2-s2.0-85023743866 (Scopus ID)
Available from: 2017-08-17 Created: 2017-08-17 Last updated: 2018-10-10Bibliographically approved
6. Flood map boundary sensitivity due to combined effects of DEM resolution and roughness in relation to model performance
Open this publication in new window or tab >>Flood map boundary sensitivity due to combined effects of DEM resolution and roughness in relation to model performance
2018 (English)In: Article in journal (Other academic) Submitted
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:hig:diva-28426 (URN)
Available from: 2018-11-08 Created: 2018-11-08 Last updated: 2018-11-09Bibliographically approved
7. A cartographic framework for visualising flood uncertainties
Open this publication in new window or tab >>A cartographic framework for visualising flood uncertainties
2018 (English)In: Article in journal (Other academic) Submitted
National Category
Other Computer and Information Science
Identifiers
urn:nbn:se:hig:diva-28427 (URN)
Available from: 2018-11-08 Created: 2018-11-08 Last updated: 2018-11-09Bibliographically approved
8. Assessment of spatial-based decisions and user perspectives in utilisation of flood certainty maps
Open this publication in new window or tab >>Assessment of spatial-based decisions and user perspectives in utilisation of flood certainty maps
(English)Manuscript (preprint) (Other academic)
National Category
Other Computer and Information Science
Identifiers
urn:nbn:se:hig:diva-28428 (URN)
Available from: 2018-11-08 Created: 2018-11-08 Last updated: 2018-11-09Bibliographically approved

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Lim, Nancy Joy

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