Urban Floods

Common global crisis

By Dr S. Saraswathi
(Former Director, ICSSR, New Delhi)

Mumbai, Chennai, Bangalore or Delhi — urban flooding has become a common recurring factor in pre-monsoon and monsoon periods thus providing flood news throughout the year. It is no consolation to read worse reports of heavy flooding even in Florida or Texas in the most advanced nation, the US. Comrades in distress cannot afford to stop with sharing their bitter experiences, but should pool their tested strategies to restrain urban flooding which has become an inevitable global phenomenon in recent decades.
A global analysis based on an exhaustive study of river systems across 160 countries shows signs of changes in stream-flow patterns causing intense flooding in cities and smaller catchments and drying up of countryside. Intense rainfalls overwhelm infrastructure, however expanded and modernized, and cause frequent urban flooding.
Climate studies, on the other hand, have found that climate change caused by global warming is the major reason behind heavy rainfall and extreme weather conditions and climate events with changes in frequency, intensity, spatial extent, duration, and timing.
A projection by the UN State of World Population indicates that by 2030, over 50 per cent of the total world population will be residing in urban areas. Asia is said to be fastest in urbanisation where population in cities which was 37 per cent of the total is likely to grow as 50 per cent by 2025. World Bank reports that five countries — India, China, Indonesia, Nigeria, and the US will lead this surge and India would see fastest growth of urban population.
India’s urban population constituted 10.8 per cent of the total population in 1901 and increased to 31.1 per cent in 2011. In the decade between 2001 and 2011, the growth was nearly 4 per cent. The increase is due both to expansion of existing cities as well as growth of new cities and towns.
The term “urbanisation”, technical definition apart, raises different images of transformation of villages into cities. The process of urbanisation that can contribute to urban floods involves human intervention in natural environment. It includes man-made modifications of natural landscape in which paving and building is an important part. In this process, the natural soil, which can absorb water, is removed. Extremely clean and well-laid concrete roads constructed in cities of western countries are highly attractive and manifest affluence of the place, but they hardly provide a shield against flood. They cannot swallow rainwater which the old rugged rural roads can easily do. There is a direct correlation between increasing urbanisation with paved and impervious roads and flooding of cities by rain.
Concretisation of roads is a luxury in India, but use of asphalt and cementing of pavements with slabs are common. If well-laid roads can cause flood, one can imagine what would be the effect of deliberate drying up of ponds and canals to raise high rise buildings for residential, commercial, and administrative purposes. Urbanisation in catchment areas can actually induce flood where there was previously no such possibility. Much worse is conversion of river beds and canal banks as garbage dumping sites reducing space for natural water flow.
Demand for housing due to continuous migration from rural areas has led to enormous growth in building construction at any available space. Rapid urbanisation increases the extent of flooded area and water depth even with no change in the quantum of rainfall. Correlation between urbanisation and urban flooding being a proven fact since 1970s, urban flooding everywhere has become a separate theme for identifying time-specific causes, impact assessments, and required remedial measures.
There is rapid rise in urban flooding in the past 15 years which itself is illustration of potential ill effects of green-house induced climate change. Many Indian cities seem to be vulnerable to flooding.
Three main factors are behind urban flooding – meteorological resulting from weather factors like heavy rainfalls; hydrological depending on presence or absence of overbank flow channel networks and occurrence of high tides impeding drainage; and deliberate human interventions like changes made in land-use pattern and rapid urbanisation without sufficient infrastructure. In the first two also, human activity is indirectly present. Some problems are common whether it is Houston or Chennai.
India has many companions in Asia in promoting urban flooding. The number of cities in China affected by floods has more than doubled since 2008 despite the fact that major rivers have remained stable. In 2003, over 200 cities in China were swamped at some point due to urban sprawl that took place faster than construction of drainage. The massive flood in Yangtzi River in the late 1990s was initially considered a rural problem overlooking the urban factor that was present even at that time.
The importance of urban drainage was lost in the concentration placed on concretisation of urban land. Construction of dams to store water from national and international rivers received priority and changing the natural course of water and introducing diversions became part of development. As a result, rainfall for just two to three hours is enough to flood many roads in urban China.
Chinese cities have expanded rapidly some of them directly on flood plains. Reclamation of rivers and lakes for development projects has gone on vigorously. There are over 150 sunken underpasses in Beijing alone inviting flood after even moderate rain.
Countries most prone to urban flooding include low-lying Netherlands, Surinam, Bahrain, Gibralter and Hong Kong. In South Africa, flooding of urban areas has become a regular geographical event every year. Low-lying Jakarta in Indonesia, where a number of rivers and canals cross, is described in a study as presenting a “never endless” history of floods. The Philippines exposes flaws in urban planning.
On top of all, hundreds of cities in the US have faced severe flooding and still face flood threats. The list of vulnerable cities includes New York, Boston, Chicago, Detroit, San Francisco, Miami besides whole States in southern US. The recent Houston flood is said to be a design problem.
While flooding of Mumbai is a regular event, flooding of Chennai in 2015 was a rare event for which the residents were totally unprepared. It threatens to become a regular event as urban expansion is continuing vigorously while necessary infrastructure is hopelessly lagging behind. Bangalore seems to follow Chennai model of expansion.
Flood disaster in all these places is man-made caused by unplanned urbanisation and unregulated encroachments. Vertical growth of inner cities is disproportionate to the existing sewerage and storm water drain network. Violation of building rules is common as deviations are accepted as normal. It is hardly realised that the policy of regularising irregular constructions amounts to inviting disasters.
AMRUT (Atal Mission for Rejuvenation and Urban Transformation) has been launched in 2015 to improve urban infrastructure in 81 cities in five states. It aims at enhancing basic infrastructure including water supply and sewerage connections in the cities taking up urban improvement as an integrated work. It is expected to eliminate the side effects of rapid urbanisation. SMART city project is also going on vigorously. These projects have to aim primarily at making cities liveable and free from development-induced disasters like floods.—INFA