atmosphere and warming of the lower atmosphere. With such a steep lapse
rate, cloud formation will be rapid and there will be more thunderstorms.
There will also be heavy precipitation, warned the IMD report.
7
More recently, UK-based Maplecroft’s Climate Change and
Environmental Risk Atlas 2013 has ranked Mumbai eighth in the global list of
total 50 cities (chosen for their current and future importance to global
business) that face a range of risks due to climate change. The 2013 atlas
clubs Mumbai under “high risk” category in the climate change vulnerability
index (CCVI). The CCVI has been developed by Maplecroft to identify risks
to populations, company operations, supply chains and investments in 197
countries. It evaluates exposure to climate related natural hazards; the sensitivity of populations; development; natural resources; agricultural dependency; research and development; government effectiveness and education
levels.
8
3.1 Mumbai’s Challenge of Staying Afloat
Mumbai has a unique topography, whereas the island city is made of merger of
seven islands, the suburbs consist of four island and some hilly areas. Much of the
city lies just above sea level, with average elevations ranging from 10 to 15 m.
A large part of the city sits upon reclaimed land (see map 1: Mumbai, an amalgamation of islands). Railway lines are typically about 10 m above low tide level
and the subways are very close to high tide level. Mumbai’s gravity drainage
system was designed in 1920s, and is affected by low and high tides. During high
tide, flood gates are closed to stop ingress of sea water. Thus, if high tide and heavy
rains occur at the same time, there is no drainage of storm water and large parts of
the city get flooded. The storm water drainage network of the city is over 100 years
old, and is designed for a rainfall of 25 mm/h and a run-off coefficient of 0.5 only
(The percentage of rainfall that appears as storm water run-off from a surface is
called the run-off coefficient). However, under present circumstances, when the city
is overdeveloped with major changes in land use pattern, the run-off coefficient has
increased to 1. The storm water drains do not have the capacity to drain out excess
water from the city.
Interestingly, both Mumbai and Singapore receive about 2500 mm rainfall per
annum. But, Singapore’s rainfall is better distributed over the year, whereas
Mumbai receives majority of rainfall during the two months of July and August.
Analysis by an ex-officer of Municipal Corporation of Greater Mumbai (MCGM)
7
http://www.downtoearth.org.in/node/3471.
8
http://maplecroft.com/about/news/ccvi_2013.html.
462
S. Manasi and N. Jamwal
rate, cloud formation will be rapid and there will be more thunderstorms.
There will also be heavy precipitation, warned the IMD report.
7
More recently, UK-based Maplecroft’s Climate Change and
Environmental Risk Atlas 2013 has ranked Mumbai eighth in the global list of
total 50 cities (chosen for their current and future importance to global
business) that face a range of risks due to climate change. The 2013 atlas
clubs Mumbai under “high risk” category in the climate change vulnerability
index (CCVI). The CCVI has been developed by Maplecroft to identify risks
to populations, company operations, supply chains and investments in 197
countries. It evaluates exposure to climate related natural hazards; the sensitivity of populations; development; natural resources; agricultural dependency; research and development; government effectiveness and education
levels.
8
3.1 Mumbai’s Challenge of Staying Afloat
Mumbai has a unique topography, whereas the island city is made of merger of
seven islands, the suburbs consist of four island and some hilly areas. Much of the
city lies just above sea level, with average elevations ranging from 10 to 15 m.
A large part of the city sits upon reclaimed land (see map 1: Mumbai, an amalgamation of islands). Railway lines are typically about 10 m above low tide level
and the subways are very close to high tide level. Mumbai’s gravity drainage
system was designed in 1920s, and is affected by low and high tides. During high
tide, flood gates are closed to stop ingress of sea water. Thus, if high tide and heavy
rains occur at the same time, there is no drainage of storm water and large parts of
the city get flooded. The storm water drainage network of the city is over 100 years
old, and is designed for a rainfall of 25 mm/h and a run-off coefficient of 0.5 only
(The percentage of rainfall that appears as storm water run-off from a surface is
called the run-off coefficient). However, under present circumstances, when the city
is overdeveloped with major changes in land use pattern, the run-off coefficient has
increased to 1. The storm water drains do not have the capacity to drain out excess
water from the city.
Interestingly, both Mumbai and Singapore receive about 2500 mm rainfall per
annum. But, Singapore’s rainfall is better distributed over the year, whereas
Mumbai receives majority of rainfall during the two months of July and August.
Analysis by an ex-officer of Municipal Corporation of Greater Mumbai (MCGM)
7
http://www.downtoearth.org.in/node/3471.
8
http://maplecroft.com/about/news/ccvi_2013.html.
462
S. Manasi and N. Jamwal