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Sahlin, Eva A. U.
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Publications (8 of 8) Show all publications
Lim, N. J., Sahlin, E. A. U. & Brandt, S. A. (2018). 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: 2019-08-07Bibliographically approved
Lim, N. J. & Sahlin, E. (2017). Quantification, classification and mapping of spatial uncertainties of floods. In: : . Paper presented at 28th International Cartographic Conference (ICC), 2-7 July 2017, Washington, D.C., USA.
Open this publication in new window or tab >>Quantification, classification and mapping of spatial uncertainties of floods
2017 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

In flood modelling studies, spatial uncertainties may be visualised differently. This will rely on the characteristics of the information produced from the quantification method applied, which may vary depending on the type of model uncertainty taken into account. It is important to be able to characterise and generally classify the different types of spatial uncertainty information in hydraulic model results, because this can help determine how they can be best represented and visualised.

In this paper, two methods of quantifying uncertainties were employed to derive uncertainty information. The first was ensemble-based modelling, which combined the results of 100 simulations considering the effects of the Digital Elevation Model (DEM) and Manning’s roughness coefficient to the model output. Each result from the individual model run was assessed on how likely it depicted the spatial extent of an observed flood event. Afterwards, the results were weighted and aggregated. In the second method, the most optimal output based on a series of calibrations from one-dimensional flood modelling was used and applied with the empirical disparity-distance equation to account for further errors brought about by the resolution of the underlying DEM and the slope. The equation was implemented with an algorithm that created uncertainty zones based on the 95% prediction confidence. The resulting information from the two quantification methods were then classified, discretised and visualised using different map types, visual variables, and overlay techniques.

Based on these results, four types of uncertainty information for flood modelling were produced that can be classified according to the characteristics of the data they show: (1) diverging, which is distinguished by two opposing conditions (certain to be dry and flooded) and a middle condition (highly uncertain); (2) sequential, where values range from lowest (uncertain) to highest (certain); (3) multiple calibration results, which show simultaneously the flood extents produced using different parameters for comparative purposes; and, (4) inundation zones which identify areas that are both certain and uncertain to be flooded.

The results from both diverging and sequential uncertainty information were presented as continuous and discrete data in choropleth and graduated symbol maps. The gradation from uncertain-to-certain conditions was displayed using lightest-to-darkest colour and/or smallest-to-largest point symbols. With certainty/uncertainty zone, the binary statuses were represented in choropleth maps as: (a) blue/red colours; (b) organised/disorganised arrangements; and, (c) fine/coarse grain textures. For multiple calibration results, isopleths maps were used with a combination of at least two visual variables (size, shape, colour) to emphasise the differences in the lines, and facilitate visual comparison of results.

Furthermore, since giving geographic context to flood uncertainty is an important aspect in the visualisation, three types of overlay were considered: map pairs, sequential and bivariate representations. Sequential representation worked well for all map types. Bivariate maps, on the other hand, were best for uncertainty represented as [one-coloured] symbol, texture, arrangement and linear features, which do not obscure the information behind. The background map had also to be displayed with increased transparency to prevent its dominance over the uncertainty data. Map pairs were the most suitable for choropleth maps using fill colour in order to avoid problems caused by colour blending when two maps are overlain. 

Classification of the uncertainty information facilitated the choice of data representation. Even when using other quantification methods, hydraulic modellers can adopt the suggested visualisation using similar characteristic data.  This can be an initial step in producing guidelines for flood uncertainty visualisation. Moreover, testing the effectiveness of these visualisations can be the next relevant step to see how the information is communicated, interpreted and used, e.g. in spatial planning, flood risk management and insurance policies.

Keywords
Flood mapping, uncertainty classification, hydraulic modelling, visualisation
National Category
Other Computer and Information Science Other Civil Engineering
Identifiers
urn:nbn:se:hig:diva-25239 (URN)
Conference
28th International Cartographic Conference (ICC), 2-7 July 2017, Washington, D.C., USA
Available from: 2017-09-14 Created: 2017-09-14 Last updated: 2018-03-13Bibliographically approved
Sarady, M. & Sahlin, E. A. U. (2016). The influence of snow cover on ground freeze-thaw frequency, intensity, and duration: An experimental study conducted in coastal northern Sweden. Norsk Geografisk Tidsskrift, 70(2), 82-94
Open this publication in new window or tab >>The influence of snow cover on ground freeze-thaw frequency, intensity, and duration: An experimental study conducted in coastal northern Sweden
2016 (English)In: Norsk Geografisk Tidsskrift, ISSN 0029-1951, E-ISSN 1502-5292, Vol. 70, no 2, p. 82-94Article in journal (Refereed) Published
Abstract [en]

The impact of snow cover on seasonal ground frost and freeze-thaw processes is not yet fully understood. The authors therefore examined how snow cover affects seasonal ground frost in a coastal setting in northern Sweden. Air and soil temperatures were recorded in a paired-plot experiment, both with and without snow cover, during the frost season 2012–2013. The frequency, duration, and intensity of the freeze-thaw cycles during the frost season were calculated. The results showed that the freeze-thaw frequency was 57% higher at the soil surface and the intensity 10 °C colder in the spring of 2013, when the ground lacked snow cover. Furthermore, the duration of the seasonal freeze-thaw cycle was 30 days longer on average in cases where there was natural snow accumulation. The correlation between air and ground surface temperatures weakened with increased snow-cover depth. The authors conclude that continued increases in air temperature and decreases in snow in coastal northern Sweden might alter freeze-thaw cycles and thus affect natural and human systems such as geomorphology, ecology, spatial planning, transport, and forestry.

Keywords
freeze-thaw, seasonally frozen ground, snow-cover, soil temperature, subarctic Sweden
National Category
Physical Geography
Identifiers
urn:nbn:se:hig:diva-21390 (URN)10.1080/00291951.2016.1154102 (DOI)000378162700002 ()2-s2.0-84961392033 (Scopus ID)
Funder
Swedish Research Council
Available from: 2016-04-06 Created: 2016-04-06 Last updated: 2018-03-13Bibliographically approved
Harrie, L., Larsson, K., Tenenbaum, D., Horemuz, M., Ridefelt, H., Lysell, G., . . . Lagerstedt, J. (2014). Some strategic national initiatives for the Swedish education in the geodata field. In: Joaquin Huerta, Sven Schade, Carlos Granell (Ed.), Connecting a Digital Europe through Location and Place: Selected best short papers and posters of the AGILE 2014 Conference, 3‐6 June 2014, Castellón, Spain. Paper presented at The 17th AGILE International Conference on Geographic Information Science, Castellón, Spain, June, 3-6, 2014. AGILE Digital Editions
Open this publication in new window or tab >>Some strategic national initiatives for the Swedish education in the geodata field
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2014 (English)In: Connecting a Digital Europe through Location and Place: Selected best short papers and posters of the AGILE 2014 Conference, 3‐6 June 2014, Castellón, Spain / [ed] Joaquin Huerta, Sven Schade, Carlos Granell, AGILE Digital Editions , 2014Conference paper, Published paper (Refereed)
Abstract [en]

This paper describes national cooperation in Sweden launched by its universities and authorities, aimed at improving geodata education. These initiatives have been focused upon providing common access to geodata, the production of teaching materials in Swedish and organizing annual meetings for teachers. We argue that this type of cooperation is vital to providing high quality education for a poorly recognized subject in a country with a relatively small population.

Place, publisher, year, edition, pages
AGILE Digital Editions, 2014
Keywords
GIS, geodata, education, teaching material, spatial data infrastructure
National Category
Other Civil Engineering Remote Sensing Geosciences, Multidisciplinary
Identifiers
urn:nbn:se:hig:diva-16919 (URN)978-90-816960-4-3 (ISBN)
Conference
The 17th AGILE International Conference on Geographic Information Science, Castellón, Spain, June, 3-6, 2014
Available from: 2014-09-26 Created: 2014-06-14 Last updated: 2018-03-13Bibliographically approved
Sahlin, E. A. .. & Glasser, N. F. (2011). The Geomorphological Map of Wales and its use in Geoconservation Assessment (poster). In: : . Paper presented at Geoconservation for Science and Society: An Agenda for the 21st Century, University of Worcester, 9-10 september, 2011.
Open this publication in new window or tab >>The Geomorphological Map of Wales and its use in Geoconservation Assessment (poster)
2011 (English)Conference paper, Published paper (Other academic)
Abstract [en]

A geomorphological map is probably the most comprehensive way of illustrating the landform distribution, surface form, material, age, and the processes responsible for the landscape look. As such geomorphological maps are invaluable in the fields of geoconservation assessment, evaluation and management. It is therefore an oddity, as well as an inconvenience, that there is no systematic landform inventory or mapping of the geomorphology that is comparable to the surveys undertaken for geology or soils in the UK. For that purpose the project of “Developing a Geomorphological Map of Wales” was initiated by the Countryside Council for Wales (CCW) as part of a PhD project investigating the Quaternary glaciations of Wales.

To develop a mapping methodology suitable for the Welsh landscape, three contrasting areas were selected to provide a wide range of geomorphological features. Aerial photography, satellite imagery, digital elevation models, and field investigations of landform/sediment associations, formed the foundation for landform interpretation, which were compiled in a GIS.

Geomorphological maps of Cadair Idris, and the Central and North Cambrian Mountains were produced, scale 1:10 000 – 1:25 000. The maps form an extensive inventory of the geomorphological geodiversity, and were used for providing data to palaeoglaciological reconstructions and making geoconservation recommendations to the CCW. The recommended sites are of regional interest; their rareness, distinct morphology, interesting research and educational value makes them worthy of RIGS (Regional Important Geodiversity Sites) protection.

A Geomorphological Map of Wales has the potential for wider practical, scientific and educational benefits, such as for governmental bodies, local authority planners, tourism, researchers, teachers, landowners and land managers. Without a full account of all the geomorphological components of a landscape, there can be no full understanding of the landscape history or the various landforming processes. Important geodiversity sites may be overlooked, badly managed or lost before their full potential are realised.

Keywords
Geoconservation, geodiversity, Geomorphological Map of Wales, landscape, palaeoglaciological reconstructions
National Category
Geosciences, Multidisciplinary Physical Geography Other Earth and Related Environmental Sciences Remote Sensing
Identifiers
urn:nbn:se:hig:diva-10520 (URN)
Conference
Geoconservation for Science and Society: An Agenda for the 21st Century, University of Worcester, 9-10 september, 2011
Available from: 2011-09-29 Created: 2011-09-28 Last updated: 2018-03-13Bibliographically approved
Sahlin, E. A. U., Glasser, N. F., Jansson, K. N. & Hambrey, M. J. (2009). Connectivity analyses of valley patterns indicate preservation of a preglacial fluvial valley system in the Dyfi basin, Wales. Proceedings of the Geologists' Association, 120, 245-255
Open this publication in new window or tab >>Connectivity analyses of valley patterns indicate preservation of a preglacial fluvial valley system in the Dyfi basin, Wales
2009 (English)In: Proceedings of the Geologists' Association, ISSN 0016-7878, Vol. 120, p. 245-255Article, review/survey (Refereed) Published
Abstract [en]

Coastal valleys in the west part of Mid-Wales, such as the Mawddach, Dysynni, Tal-y-Ilyn and Dyfi, acted as corridors for ice which drained the Welsh Ice Cap during the Devensian. Analyses of detailed digital elevation models, and interpretation of satellite images and aerial photographs, show the existence of large variations in the amount of glacial modification between these valleys. Although all the valleys are glacially over-deepened along late Caledonian fault lines, only the Dyfi basin exhibits a dendritic pattern, with V-shaped cross-profiles and valley spurs typical of valleys formed by fluvial processes. Connectivity analysis of the Dyfi basin shows that it exhibits an almost completely dendritic pattern with connectivity alpha and beta values of 0.74 and 1.01, respectively, with little glacial modification of the preglacial fluvial valley pattern in the form of glacial valley breaching. Several examples of glacial meltwater incision into a well-developed pre-existing river valley system, causing river capture across watersheds, have been identified in the Dyfi basin. The degree of preservation of the preglacial fluvial valley system within the Dyfi basin indicates limited modification by glacial processes, despite the area being subjected to glacier activity during the Late Devensian at least. It is possible that major parts of the basin were covered by cold-based or slow-moving ice, close to, or under, a migrating ice-divide, with the major ice drainage Occurring along the weaker zone of the Pennal Fault along which teh Dyfi valley is located, causing minor adjustments to the Surrounding interfluves and uplands. it is proposed here that the general river valley morphology of the Dyfi basin is of a pre-Late Devensian age. (C) 2009 The Geologists' Association. Published by Elsevier Ltd. All rights reserved.

Keywords
Valley connectivity, Palaeoglaciological reconstruction, Glacial erosion, Preglacial drainage pattern, Dyfi, Wales
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:hig:diva-10293 (URN)10.1016/j.pgeola.2009.10.001 (DOI)000273184800007 ()2-s2.0-71749116816 (Scopus ID)
Available from: 2011-09-22 Created: 2011-09-21 Last updated: 2018-03-13Bibliographically approved
Sahlin, E. A. .., Glasser, N. F., Hambrey, M. J. & Jansson, K. N. (2009). Connectivity analyses of valley patterns reveal Devensian glacial drainage activity in Mid-Wales (poster). In: : . Paper presented at British Society for Geomorphology Conference, Durham University, 7-9 September, 2009.
Open this publication in new window or tab >>Connectivity analyses of valley patterns reveal Devensian glacial drainage activity in Mid-Wales (poster)
2009 (English)Conference paper, Published paper (Other academic)
Abstract [en]

Coastal valleys in the west part of Mid-Wales, such as the Mawddach, Dysynni, Tal-y-llyn and Dyfi, are believed to have acted as corridors for ice which drained the Welsh Ice Cap during the Devensian. Connectivity analyses of valley patterns from detailed digital elevation models, and interpretation of satellite images and aerial photographs show the existence of large variations in the amount of glacial modification between these valleys. Although all the valleys are glacially over-deepened along Silurian fault lines, only the Dyfi basin exhibits a dendritic pattern, with V-shaped cross profiles and valley spurs typical of valleys formed by fluvial processes.

The connectivity analyses show that the Dyfi basin exhibits a purely dendritic pattern with little glacial modification of the preglacial fluvial valley pattern in form of valley breaching. It is proposed here that the general river valley morphology of the Dyfi basin is of a pre-Late Devensian age. This suggests a complex glacial drainage history, where cold-based ice was not only confined to the interior uplands, but also covered low-altitude areas previously believed to be a major drainage conduit for the Welsh Ice Cap. This indicates that Late Devensian glacial erosion was not as intense as previously believed and larger areas might have been overlain by cold-based ice.

Keywords
Valley connectivity, glacial reconstructions, Late Devensian, Wales
National Category
Physical Geography Geosciences, Multidisciplinary Climate Research Remote Sensing
Identifiers
urn:nbn:se:hig:diva-10523 (URN)
Conference
British Society for Geomorphology Conference, Durham University, 7-9 September, 2009
Available from: 2011-09-29 Created: 2011-09-28 Last updated: 2018-03-13Bibliographically approved
Sahlin, E. A. .., Glasser, N. F., Jansson, K. N. & Hambrey, M. J. (2009). Evidence for cold-based ice at low altitudes: Preservation of a preglacial fluvial valley system in the Dyfi basin, Wales (poster). Paper presented at The International Glaciological Society British Branch 34th Annual Meeting, University of Sheffield, 2-3 September, 2009.
Open this publication in new window or tab >>Evidence for cold-based ice at low altitudes: Preservation of a preglacial fluvial valley system in the Dyfi basin, Wales (poster)
2009 (English)Conference paper, Published paper (Other academic)
Abstract [en]

Coastal valleys in the west part of mid-Wales, such as the Mawddach, Dysynni, Tal-y-llyn and Dyfi, are believed to have acted as corridors for ice which drained the Welsh Ice Cap during the Devensian. Analysis of detailed digital elevation models and interpretation of satellite images and aerial photographs show the existence of large variations in the amount of glacial modification between these valleys. Although all the valleys are glacially over-deepened along Silurian fault lines, only the Dyfi basin exhibits a dendritic pattern, with V-shaped cross profiles and valley spurs typical of valleys formed by fluvial processes. Connectivity analysis of the Dyfi basin shows that it exhibits a nearly dendritic pattern with connectivity α and β values of 0.74 and 1.01 respectively, with little glacial modification of the preglacial fluvial valley pattern in the form of valley breaching. It is proposed that the general river valley morphology of the Dyfi basin is of a pre-Late Devensian age. Several examples have been identified of glacial meltwater incision into a well-developed pre-existing river valley system, causing river capture across watersheds. The degree of preservation of the pre-glacial fluvial valley system within the Dyfi basin indicates limited modification by glacial processes, despite the area being subjected to Late Devensian glacier activity. It is possible that major parts of the basin were covered by cold-based or slow-moving ice close to or under a migrating ice divide, with the major ice drainage occurring along the weaker zone of the Pennal Fault, causing minor adjustments to the surrounding interfluves and uplands.

Keywords
Palaeoglaciological reconstruction, glacial erosion, preglacial drainage pattern, Wales.
National Category
Physical Geography Climate Research Geosciences, Multidisciplinary Remote Sensing
Identifiers
urn:nbn:se:hig:diva-10522 (URN)
Conference
The International Glaciological Society British Branch 34th Annual Meeting, University of Sheffield, 2-3 September, 2009
Available from: 2011-09-29 Created: 2011-09-28 Last updated: 2018-03-13Bibliographically approved
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