İnci Güneralp, Burak Güneralp, & Ying Liu, Texas A&M University, College Station, TX, USA

Presentation Title: Changing global patterns of urban exposure to flood and drought hazards




Studies that quantify the human and economic costs of increasing exposure of cities to various natural hazards considering climate change, an increasing population and economic activity assume constant urban extent. Accurate estimates of the potential losses due to changing exposure of cities, however, require that we know where they will grow in the future. This research offers the first-ever estimates of changing exposure of urban infrastructure to floods and droughts due to urban land expansion from 2000 to 2030. The findings show that even without factoring in the potential impacts from climate change, the extent of urban exposure to flood and drought hazards will increase by 2.7% and almost double, respectively, by 2030. Several policy options exist to safeguard urban infrastructure from flood and drought hazards. These range from directing development away from flood- or drought-prone zones to large-scale adoption of 'green infrastructure'. 

Key Lessons Learned

  • Knowing where cities will grow is important to understand how their exposure to hazards will change.
  • Emerging coastal metropolitan regions in Africa and Asia will have larger areas exposed to flooding than those in developed countries.
  • Even without climate change, the extent of urban areas exposed to floods and droughts would at least double by 2030.

Policy/Practice Implications of Research

  • Decisions made today on managing urban growth in locations exposed to these hazards can make a big difference in mitigating likely losses due to floods and droughts in the near future.
  • Although forecasts show significant urban expansion in high-frequency flood zones, governments can potentially preempt these patterns and prevent development in flood-prone zones. This would protect natural habitats that would reduce flooding at a considerable cost (assuming institutional and financial capacity to undertake these actions exist).
  • In countries located in arid regions, national governments can implement ambitious plans to bring water to their growing cities if they have access to sufficient financial resources.
  • In cities located in drylands, water loss due to leakage from water distribution systems becomes especially troublesome in drought episodes during which excessively dry soils exert pressure on building foundations, transportation systems, pipes, and joints. It will be important to minimize such losses by increasing the efficiency and effectiveness of monitoring and maintenance of the infrastructure – both new and existing.
  • To minimize the risks to urban infrastructure posed by unforeseen changes in demands and environmental conditions, future urbanization presents an opportunity for large-scale adoption of 'green infrastructure' or 'eco-efficient infrastructure' that represent long-standing principles of durability, flexibility and energy-efficiency in infrastructure construction.

Knowledge Gaps and Needs

  • A challenge in research on global environmental change is the incorporation of feedbacks among the socio-economic and biophysical systems as well as the uncertainty inherent in any forward-looking assessment.
  • A more comprehensive, systems-oriented study of flood and drought hazards is needed to understand the potentially compounding impacts of socio-economic and biophysical dynamics on people and infrastructure that account for humans’ impact on water and climate.
  • The influence of humans in the form of water abstraction, land change, and the construction of large infrastructure on regional and global hydrology remain largely absent in the current studies. Incorporation of these interactions and accounting for uncertainty would lead to an informed understanding of exposure and vulnerability in urban areas as well as how these will change in over time.
  • Overcoming the challenges of inherent limitations to urban expansion forecasts, e.g., excluding potential changes in transportation networks associated with urban development and ignoring differences among various urban land uses or between formal and informal growth, could better inform exposure and vulnerability assessments as well as decision-making.
  • A potential improvement to the global urban forecasts used in this study would be to utilize a scenario approach where each urban expansion scenario is linked to a specific representative concentration pathway (RCP) employed by the IPCC, thereby ensuring consistency, accurate accounting of uncertainty and the incorporation of the feedbacks between socio-economic and biophysical components.