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Remote sensing estimates of impervious surfaces for hydrological modelling ofchanges in flood risk during high-intensity rainfall events

Kaspersen, Per Skougaard; Fensholt, Rasmus; Drews, Martin

Publication date:2014

Document VersionPeer reviewed version

Link back to DTU Orbit

Citation (APA):Kaspersen, P. S., Fensholt, R., & Drews, M. (2014). Remote sensing estimates of impervious surfaces forhydrological modelling of changes in flood risk during high-intensity rainfall events. Poster session presented atIARU Sustainability Science Congress, Copehagen, Denmark.

Per Skougaard Kaspersen1, Rasmus Fensholt2, Martin Drews1 1Technical University of Denmark (DTU), 2University of Copenhagen (KU)

INTRODUCTION

References - Angel, S., Parent, J., Civco, D. L., Blei, A., & Potere, D. (2011). The dimensions of global urban expansion: Estimates and projections for all

countries, 2000–2050. Progress in Planning, 75(2), 53–107. doi:10.1016/j.progress.2011.04.001

- Arnold, C. L., & Gibbons, C. J. (1996). Impervious Surface Coverage: The Emergence of a Key Environmental Indicator. Journal of the

American Planning Association, 62(2), 243–258. doi:10.1080/01944369608975688.

- IPCC (2012). Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. A Special Report of Working

Groups I and II of the Intergovernmental Panel on Climate Change [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D.

Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, UK, and

New York, NY, USA, 582 pp.

- Weng, Q. (2012). Remote sensing of impervious surfaces in the urban areas: Requirements, methods, and trends. Remote Sensing of

Environment, 117, 34–49. doi:10.1016/ j.rse.2011.02.030.

CONCLUSION

As major European urban areas are almost exclusively characterized by a combination of impervious

surfaces and green vegetation, information on vegetation cover from remote sensors can be utilised to

provide accurate and cost-efficient estimates of the quantity and spatial distribution of impervious surfaces

and changes herein. Such information is useful for a wide range of applications including analysis of the

importance of urbanisation for the exposure of cities towards the occurrence and impacts of climate

extremes, such as flooding during high-intensity rainfall events.

METHODOLOGY

Information on the extent and quantity of vegetation cover

is used to provide estimates of sub-pixel imperviousness

for several urban areas in Europe. This is based on the

assumption of a strong inverse relationship between

vegetation cover and impervious surface, i.e. it is implicitly

assumed that non-impervious surfaces within urban areas

are covered with green vegetation.

Three different Landsat-based datasets (NDVI, SAVI and

fractional vegetation cover) have been developed based

on information on vegetation cover from the Landsat 8

sensor. Eight cities are analyzed in the following,

representing the major vegetative and climatic conditions

in Europe. The accuracy and spatial transferability

potential of the three methods are evaluated at 30m

spatial resolution. Landsat satellite imagery is publicly

available and covers the period from 1972 and onwards. IMPERVIOUS SURFACE MAPPING

Remote sensing estimates of impervious surfaces for hydrological modelling of changes in flood risk during high-intensity rainfall events

Abstract

Impervious surfaces (IS) such as road infrastructure,

buildings and other paved areas typically dominate urban

environments (Weng, 2012) and subsequently are often

used as an indicator of urbanisation (Angel et al., 2011).

IS may generally be defined as man-made surfaces

through which water cannot infiltrate. The quantity and

location of impervious surfaces within urban areas are

important for the hydrological response during high-

intensity rainfall as it affects the amount and velocity of

run-off, and consequently influences the exposure of

cities towards flooding (Arnold and Gibbons, 1996). For

this reason past and present city development patterns

may prove to have had (and will continue to have)

important implications for the exposure of urban systems

to the risk of flooding. At the same time, climate change is

expected to increase the frequency and intensity of

extreme rainfall events in many locations and thus further

increase the exposure of cities to flooding

(Intergovernmental Panel on Climate Change, 2012).

Increased knowledge of the importance of both urban

land cover changes and climate change for the risk of

urban areas towards flooding will provide substantial

insight to city administrations and governments in how to

plan for future climate proof cities.

This paper addresses the accuracy and applicability of

medium resolution (MR) remote sensing estimates of

impervious surfaces (IS) for urban land cover change

analysis. Landsat-based vegetation indices (VI) are found

to provide fairly accurate measurements of sub-pixel

imperviousness for urban areas at different geographical

locations within Europe, and to be applicable for cities with

diverse morphologies and dissimilar climatic and

vegetative conditions. Detailed data on urban land cover

changes can be used to examine the diverse

environmental impacts of past and present urbanisation,

including the importance of such changes for the exposure

of cities towards the occurrence and impacts of climate

extremes like high-intensity rainfall events.

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Exeter

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Oslo

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Exeter

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Hamburg

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Odense

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Hamburg

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Odense

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Strasbourg

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Nice

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Strasbourg

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Nice

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Vienna

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Barcelona

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Barcelona

Refe

ren

ce IS

(%

)

NDVI SAVI Linear Perfect fit

Landsat-based imperviousness (%)

Ob

serv

ed im

pe

rvio

usn

ess (

%)

NDVIHigh : 0.8

Low : 0

Impervious surface (%)

High : 100

Low : 0

Obs. imperviousness - high-resolution imagery

Vegetation - Landsat 8 satellite imagery

Reg

ress

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mo

del

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¯¯

¯ ¯

STUDY AREAS

Mean bias error (%)

Mean absolute error (%)

ACCURACY ASSESSMENT DATA & ANALYSIS PROCEDURES

Urban sub-areas included in the analysis

IMPACT OF URBANISATION ON FLOOD RISK (ongoing work) OVERVIEW OF FLOOD MODEL SIMULATIONS LAND COVER CHANGE ANALYSIS

Change in imperviousness- City of Odense 1984-2014

-79.9 - -60

-59.9 - -40

-39.9 - -20

-19.9 - -10

-9.9 - 10

10.1 - 20

20.1 - 40

40.1 - 60

60.1 - 80

80.1 - 100

-100 - -80

Absolute

change (%)

FLOOD HAZARD MAPPING

8.6 8.1

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Observed imperviousness (%)

NDVI

SAVI

FR

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Observed imperviousness (%)

NDVI

SAVI

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Flooding in the city of Odense during high-intensity rainfall occurring once

every 100 years (RP100)

Flood risk with urban

land cover as in 1984

Change in flood risk due to

urbanisation (1984-2014)

Change in flood risk due

to climate change (RCP

8.5, ≈ +3.5C)

Maps are produced by VCS Denmark for the municipality of Odense

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