What Is the Triple Threat and How Does It Affect

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The Answer is Flooding is an emerging urban challenge due to what researcher Tapan Dhar labels the triple threat: a hazard-prone location; loss of natural systems of water filtration and absorption; and weak planning and infrastructure management. Many cities are located along the water; with sea-level rise, glacial melting, and an increased severity and frequency of storms, urban flooding has increased. Dhaka, the ninth largest megacity with 20 million people, is illustrative. Floods occur annually, with particularly catastrophic events in 1998 and 2004. Tapan Dhar argues that the severity of flooding will likely increase for three intertwined reasons. First, the city's location, climate, and topography make it prone to flooding. Dhaka's monsoons bring 2000 mm of heavy rains between June and September; rainfall is expected to increase 16 per cent by 2050. Because it is located on a river delta with a flat, low-lying topography, monsoon rainwater and river spillover combine to exceed the absorption capacity of soil surfaces. Second, Dhaka, like other large cities, has lost many of the natural systems that absorb and slowly release water. Wetlands, green areas, and bodies of water have decreased in size. Agriculture upstream contributes to siltation of rivers and decreased capacity to channel water. Population growth plays a role too. An estimated 500,000 people move to Dhaka each year. Many are environmental refugees, displaced by land erosion along inland rivers or forced to flee coastal areas where cyclones, sea-level rise, and associated salt-water intrusion have rendered water unsafe to drink. Population growth pushes the city's built-up area into flood-prone and wetland zones. Dhaka Metropolitan Area (DMA) lost nearly 77 per cent of its wetlands and 19 per cent of rivers and canals between 1978 and 2009 because of speculative property development and informal settlement. Third, poor infrastructural management and settlement patterns reinforce a heightening of risk and its distribution to the detriment of the poor. Road and building construction renders surfaces less permeable to water, compounding the loss of natural water retention areas. The Dhaka Structure Plan (2016-35) includes comprehensive and integrated planning for flood management, but it is yet to be implemented. Risks are particularly high for new immigrants and low-income households; 40 per cent of the population live in informal settlements that are constructed illegally in low-lying flood-prone areas lacking municipal water and sanitation services.

What Is the Triple Threat and How Does It Affect

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What Is the Triple Threat and How Does It Affect

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