Urban Growth and Long-Term Changes in Natural Hazard Risk

Abstract

This paper explores the question of whether natural hazard risks for urban areas are growing or diminishing over time. While trends sueh as population growth in hazardous areas increase the potential for loss in disaster events, other factors, such as improved building codes, tend to reduce this risk. The net effects of sueh urban changes are examined through the use of simulation models that estimate disaster losses. In a comparative static approach, losses are modeled for the same hypothetical hazard event striking at different points in an urban area's development history. The analysis focuses on a case study of seismic hazard for the metropolitan area of Vaneouver, Canada. Results of a casualty-estimation model applied retrospectively indicate that, for the same M7.3 seismic event, human casualties would have been similar if the earthquake had struek in 2006 as in 1971, even though the population at risk had doubled in the interim. This improvement in per capita casualty rate is largely due to building-code upgrades and changes in new construction. Other dimensions of risk worsened, however: the estimated population in significantly damaged buildings increased by some 60% for the region and, in some fast-growing municipalities, more than doubled. Using a similar analytical approach, a second modeling effort focused on transportation systems and considered the risk implications of future growth. Analysis compared transportation disruption in 2004 and 2021 for a constant earthquake hazard but a forecast 21% increase in traffic. Results indicate that, for the Vancouver metropolitan area overall, disaster risk to transportation is expected to decrease slightly due to the shifting geography of residences and workplaces. The spatial distribution of risk would change, however: in particular, it would worsen for the older urban core. Moreover, the relative importance of key bridges changed over time. The analyses here indicate that in this case study, risk is not worsening significantly overall but is undergoing notable spatial redistribution; however, the extent to which this finding can be generalized to other urban areas and types of hazards remains to be investigated.

Review Article: A Comparison of Flood and Earthquake Vulnerability Assessment Indicators

“…Zevenbergen et al, 2008). Chang et al (2012) studied temporal changes in the seismic risk of Vancouver (Canada). Using a M7.3 earthquake scenario, this study concludes that despite increasing exposure (the population of Vancouver doubled over the 505 course of the 35-year study period from 1971 to 2006), the estimated 2006 casualties remained equal to the estimated number of casualties in 1971.…”

General comments and reply to reviewer #1

“…Therefore, the focus has shifted to assessing vulnerability over time (Jongman et al, 2015), but knowledge gaps continue to exist (Connor and Hiroki, 2005;McEntire, 2005;Birkmann, 2007;Cutter et al, 2008;Balica et al, 2012;Mechler and Bouwer, 2014;Jongman et al, 2015;Koks et al, 2015b). Chang et al (2012) studied temporal changes in the seismic risk of Vancouver (Canada). Using a M7.3 earthquake scenario, this study concludes that despite increasing exposure (the population of Vancouver doubled over the course of the 35-year study period from 1971 to 2006), the estimated 2006 casualties remained equal to the estimated number of casualties in 1971.…”

Defining Extreme Events: A Cross‐Disciplinary Review

“…More recently, we are experiencing an increase in disasters (Figure ; United Nations Office for Disaster Risk Reduction [UNISDR], ), which are hazards or events that generate impacts on our social, ecological, and/or technical systems. While the number of deaths has not been increasing, there have been observed increases in the total number of people affected and monetary damages (Chang et al, ; UNISDR, ). This increase in disasters can be partly explained by considering the expansion of cities and suburban areas into hazard‐prone zones, and the subsequent increased exposure of people and infrastructure (Bouwer, ; Chang & Franczyk, ; Intergovernmental Panel on Climate Change [IPCC], ).…”

“…Taken together, these studies suggest that cities are a critical locus of exposure, risk, and vulnerability to extreme events. Some of these exposures have been mitigated by improved engineering solutions and early forecast technology, helping to reduce loss of lives and some financial and infrastructural impacts (Chang et al, ; Fuchs et al, ; Wilby & Keenan, ). Cities also are at the forefront of efforts to build resilience to climate change and other threats (Rosenzweig et al, ).…”