Urbanization and climate change impacts on future urban flood risk in Can Tho city, Vietnam

Abstract

Urban development increases flood risk in cities due to local changes in hydrological and hydrometeorological conditions that increase flood hazard, and also to urban concentrations that increase the vulnerability. The relationship between the increasing urban runoff and flooding due to increased imperviousness better perceived than that between the cyclic impact of urban growth and the urban rainfall via microclimatic changes. The large-scale, global impacts due to climate variability and change could compound these risks. We present the case of a typical third world city – Can Tho (the biggest city in Mekong River Delta, Vietnam) – faced with multiple future challenges, namely: (i) climate change-driven sea-level rise and tidal effect, (ii) increase river runoff due to climate change, (iii) increased urban runoff driven by imperviousness, and (iv) enhancement of extreme rainfall due to urban growth-driven micro-climatic change (urban heat islands). A set of model simulations were used to assess the future impact of the combination of these influences. Urban growth of the city was projected up to year 2100 based on historical growth patterns, using a land-use simulation model (Dinamica-EGO). A dynamic limited-area atmospheric model (WRF), coupled with a detailed land-surface model with vegetation parameterization (Noah LSM), was employed in controlled numerical experiments to estimate the anticipated changes in extreme rainfall patterns due to urban heat island effect. Finally, a 1-D/2-D coupled urban-drainage/flooding model (SWMM-Brezo) was used to simulate storm-sewer surcharge and surface inundation to establish the increase in the flood risk resulting from the changes. The results show that, if the city develops as predicted, the maximum of inundation depth and area in Can Tho will increase by about 20%. The impact of climate change on inundation is more serious than that of urbanization. The worse case may occur if the sea level rises 100 cm and the flow from upstream happen in the high-development scenarios. The relative contribution of causes of flooding are significantly different at various locations; therefore, detailed research on adaptation are necessary for the future investments to be effective

Structuring Climate Adaptation through Multiple Perspectives: Framework and Case Study on Flood Risk Management

“…The city is also likely to be affected by an increase in river water levels due to sea level rise; an increase in river discharge due to increase in rainfall, deforestation and river training works upstream; and an increase in urban runoff due to rainfall and increased imperviousness [77][78][79][80]. The rapid urban development in Can Tho has led to unplanned growth, increase in real estate prices, widespread water pollution and flooding issues and prevailing social disparities in terms of availability of housing stocks and access to services among the residents [81].…”

“…Considerable research has also been conducted in the City that considers multiple perspectives-vulnerability reduction, institutional, planning, water quality, infrastructure improvements-concerning climate change and adaptation at multiple levels [19,55,58,77,81,[85][86][87][88]. The traditional engineering perspective is reflected in the recent flood risk management plans that are being prepared and considered for implementation, where the emphasis is more on avoiding floods by means of: (i) dike rings; (ii) improvements to drainage systems; (iii) and increasing the freeboard of flood defence systems, roads and houses by 50 cm [55,85,89].…”

“…External factors such as sea level rise and rainfall increases lead to increases in flood depth and frequency [77,78,80]. Externalities such as economic growth rates influence: (i) urbanisation which in turn has a direct bearing on increasing imperviousness and enhanced runoff in Can Tho [77]; (ii) economic status such as household income and number of poorer households [92,93]. The repercussions of macro-economic growth in Can Tho may be observed in the recent trends in the population increasing due to migration, urbanisation, social disparity in terms of income and real estate prices [81].…”

“…Considerable research has also been conducted in the City that considers multiple perspectives-vulnerability reduction, institutional, planning, water quality, infrastructure improvements-concerning climate change and adaptation at multiple levels [19,55,58,77,81,[85][86][87][88]. The traditional engineering perspective is reflected in the recent flood risk …”

Integrated design workflow and a new tool for urban rainwater management

“…The subsequent urban flooding with increased frequency and severity is exacerbated by the climate change, which causes amplified magnitude of rainfall intensity in some parts of the world (Dore, 2005;Villarreal et al, 2004). The resultant urban flooding causes exceptionally severe damage where massive, rapid urbanization is occurring due to poorly engineered infrastructure (Huong and Pathirana, 2011;Liu, 2009;Wang, 2001). To address this urgent concern, it is crucial for architects and landscape designers to have a greater understanding and modeling capability of stormwater runoff to face the increasing risks in the future.…”