Projecting Future Flood Risk in Mega Cities: Application of a Spatially Explicit Urban Growth Model to Assess the Future Risk Profile of 18 Fast Growing Mega Cities. (PAP014781)

Código

PAP014781

Autores

William Veerbeek

Tema

Flood risk management in mega cities

Resumo

Many studies show that the unprecedented urban growth of metropolitan areas in especially developing countries often increases the exposure and sensitivity to floods and other natural hazards. Yet most studies about future consequences of urban development are limited to statistical growth projections, often focusing on delta cities and sea level rise. The explicit geographic changes caused by urban growth are often neglected in larger comparative studies. However, depending on the the local geographic and socio-economic conditions, the spatial patterns of urbanization differ substantially between cities. Thus, the subsequent risk profile also changes over time and is likely to be significantly different from a projected risk based on a mere statistical extrapolation from past trends. In the EU funded Collaborative Research on Flood Resilience in Urban areas, spatially explicit growth scenarios have been developed for a set of fast growing Asian megacities, including Beijing, China, Dhaka Bangladesh and Mumbai, India. Using a medium (2025) and long term (2050) horizon, business-as-usual projections have been developed based on local spatial trends of the past 20 years. The models to develop the projections are based on complex machine learning algorithms that derive land use and land cover transition rules from past spatial data. Calibration of the models is performed by comparing the goodness-of-fit between recent observed land use and land cover maps and the predicted maps. After this fit is evaluated as sufficient, future projections are created with 5 year intervals. The initial set of projections for fast growing megacities has been extended to cover a total of 18 megacities. Fast growing was defined as areas with annual growth rates of exceeding 2%. Within the current project scope, the outcomes in relation to flood risk have been focused on analyzing the position and coverage of the produced urban extents within the respective catchments, including an estimation of the subsequent changes in impervious surface ratios and an assessment of the expected population at risk. Although schematic, this provides a first insight in the relative changes in exposure and sensitivity of the expanding urban area to increased surface runoff, river floods and to some extent to landslides. The initial outcomes show that the metropolitan areas of Dhaka, Bangladesh, Jakarta, Indonesia, Guangzhou, China, Kolkata, India, Manila, Philippines and Mumbai, India disproportionally increase their flood risk profile when the current growth trends are continued into the future. Other fast growing cities show a relative decrease of flood risk due to extensive fragmentation. This is most strongly observed in Kolkata, India. In most of the investigated cities, the investments in the urban drainage network fall increasingly short to compensate the expected growth. Integration of flood risk in future urban development plans is often limited. An additional problem is that in many cities, zoning and urban containments plan are only partially effective; most of the growth in these cities is uncontrolled illustrated by vast slum areas as well as upper class suburban sprawl.