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When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk UNIVERSITY OF SOUTHAMPTON FACULTY OF SOCIAL AND HUMAN SCIENCES Geography and Environment Spatiotemporal population modelling to assess exposure to flood risk by Alan D. Smith Thesis for the degree of Doctor of Philosophy March 2015 UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF SOCIAL AND HUMAN SCIENCES Geography and Environment Thesis for the degree of Doctor of Philosophy SPATIOTEMPORAL POPULATION MODELLING TO ASSESS EXPOSURE TO FLOOD RISK Alan Daniel Smith There is a growing need for high resolution spatiotemporal population estimates which allow accurate assessment of population exposure to natural hazards. Populations vary over range of time scales and cyclical patterns. This has important implications for how researchers and policy makers undertake hazard risk assessments. Traditionally, static population counts aggregated to arbitrary areal units have been used. This thesis shows that these are inadequate for the purposes of hazard risk assessments concerning dynamic populations. This thesis enhances and applies spatiotemporal modelling techniques developed through the Population 24/7 project and integrates the outputs with hydrological models using a loose-coupling approach. This is demonstrated through two case studies to illustrate the impacts for flood risk assessment. These case studies exemplify population fluctuations according to diurnal, weekly and seasonal cycles. The considerably enhanced spatiotemporal population model constructed demonstrates a much wider flexible framework. This thesis establishes that there is a strong requirement to consider time-specific populations for the purposes of flood hazard risk analyses. Population movements have been shown to account for major variations in exposure estimates through the analysis of a range of flood scenarios and population case studies. Significant enhancements can be sought for risk analyses by using spatiotemporal population estimates. i Contents Abstract..................................................................................................................................... i Contents ................................................................................................................................ iii List of Tables .......................................................................................................................ix List of Figures .....................................................................................................................xi Declaration of Authorship ......................................................................................... xv Acknowledgements ...................................................................................................... xvii Definitions and Abbreviations ............................................................................... xix Chapter 1: Introduction ............................................................................................ 1 1.1 Population exposure to natural hazards ............................................. 3 1.2 Aims and objectives ........................................................................... 6 1.2.1 Specific objectives ......................................................................... 6 1.3 Thesis structure ................................................................................. 7 Chapter 2: Literature review ............................................................................... 11 2.1 Overview .......................................................................................... 13 2.2 Natural hazards ................................................................................ 13 2.2.1 Natural hazards and disasters ..................................................... 17 2.2.2 Vulnerability versus exposure ..................................................... 21 2.2.3 Susceptibility............................................................................... 22 2.2.4 Resilience .................................................................................... 23 2.2.5 Introducing risk .......................................................................... 25 2.2.6 Voluntary and involuntary risk exposure ..................................... 25 2.2.7 Calculating risk ........................................................................... 27 2.2.8 Risk management and emergency preparedness ......................... 28 2.2.9 Risk perception and communication ............................................ 30 2.2.10 Hazard spatiotemporal characteristics ......................................... 32 2.3 Flooding in the United Kingdom ....................................................... 36 2.3.1 Types and causes of flooding ...................................................... 36 2.3.2 Climate change and flooding ....................................................... 38 2.3.3 Recent flood history .................................................................... 39 2.3.4 The Pitt Review ............................................................................ 44 2.3.5 Management and mapping .......................................................... 45 iii 2.4 Spatial interpolation of population data ............................................ 47 2.4.1 Representing population data ...................................................... 47 2.4.2 Limitations of zonal data ............................................................. 51 2.4.3 Point-based interpolation ............................................................ 53 2.4.4 Kernel density estimation ............................................................ 53 2.4.5 Point pattern analysis .................................................................. 56 2.4.6 Kriging ........................................................................................ 57 2.4.7 Spline functions .......................................................................... 58 2.4.8 Distance-weighting ...................................................................... 58 2.4.9 Area-based interpolation ............................................................. 59 2.4.10 Areal weighting ........................................................................... 59 2.4.11 Pycnophylactic interpolation ........................................................ 60 2.4.12 Dasymetric mapping ................................................................... 62 2.4.13 Alternative representation of population data .............................. 65 2.4.14 Relating population mapping and risk exposure .......................... 67 2.5 Interpolation of population data with time ........................................ 71 2.5.1 Time ........................................................................................... 72 2.5.2 Time-geography .......................................................................... 73 2.5.3 Time GIS...................................................................................... 79 2.5.4 Analytical and simulation tools .................................................... 84 2.5.5 Space-time kriging....................................................................... 86 2.5.6 National Population Database ...................................................... 87 2.6 Spatiotemporal interpolation of population data ............................... 89 2.7 Space and time in populations exposed to natural hazards ............... 93 2.7.1 Population 24/7: spatiotemporal modelling concepts .................. 96 Chapter 3: Methods and Data............................................................................. 99 3.1 Overview ........................................................................................ 101 3.2 Modelling Population, Population 24/7 and data structure .............. 105 3.2.1 Origin centroids ........................................................................ 106 3.2.2 Destination centroids ................................................................ 107 3.2.3 Temporal profiles ...................................................................... 109 3.2.4 Wide Area Dispersion (WAD) ...................................................... 110 3.2.5 Background masking layer......................................................... 111 3.3 Applied example: Southampton, UK ................................................ 113 3.3.1 United Kingdom census origin centroids ................................... 114 3.3.2 Temporal profile creation .......................................................... 115 3.3.3 Time Profile for UK retail destinations ....................................... 117 3.3.4