This “synchronous failure” case study suggests the impact that three key drivers and one potential shock could have on a densely populated and highly complex urban area in South Asia. As evidenced in the July 2005 Maharashtra floods, the links between the flood’s impact upon the economy and the increased impoverishment of a significant portion of Mumbai’s population is difficult to calculate. Nevertheless, the drivers – ie, demographic transitions, epidemics, and water management failures along side a shock of consecutive extreme precipitation – offer a plausible projection of affected peoples in 2015. 

Background:The Maharashtra floods of July 2005 affected large areas of the metropolis of Mumbai, located on the western coast, in which at least 1,000 people died, 20 million people were affected in the region, and around $3.3bn of damage was casued. The floods were caused by the eighth heaviest ever recorded 24-hour rainfall figure of 944 mm (37.2 inches), peaking on 26 July 2005. 

Crisis drivers:There are three plausible and interactive drivers that contribute to an estimate of the numbers that would be affected in the years 2010 and 2015 by similar weather events:

[i] demography: while India’s main industrial centre in relative terms is not a poor region overall, extremely large numbers are living in slums around thecapital. There is every indication to suggest that these figures will grow(Figure 19).

Figure 19: Case Study #2; Mumbai – Forecast Increase in Slum Population 2000-2015

By population increase alone, Mumbai will incorporate an extra 3.7 million people by 2015.  Insofar as the July 2005 floods affected the entire city’s population; such an event in 2015 would affect, and therefore require assistance for, a population 20% larger.  Population growth has caused haphazard urban development, with no overall urban plan for many of the new suburban developments. 

[ii] water management: Projected frequency of extreme weather events will have a growing impact on water management failures as reflected in increased flooding. The assumption attached to this forecast is that efforts to maintain the urban infrastructures, in this case principally sewage and water systems, will not be able to keep pace with the flood events themselves and the continued growth of the city’s population.

Flooding as indicated in Figure 20, below, is also becoming more frequent, putting severe strains on natural (eg, mangrove barriers) and manmade (eg, seawalls and drainage systems) forms of flood protection. In 2015 it is likely that flood-prone areas of South Asia will see an increase in flood frequency by up to half as many flood events again annually (Figure 20).  An increase of both extreme precipitation events and Monsoon rain variability is anticipated by the IPCC. 

Figure 20:  South Asia Regional Analysis – Annual Frequency of Floods 1975-2015

Source EM-Dat

[iii] Epidemics  Rain water from the 2005 floods caused sewage systems to overflow and contaminated water lines. The storm-water drainage system in Mumbai was capable of carrying a daily maximum runoff equivalent to 600mm rainfall, clearly inadequate for the 944mm seen on that day.  Where the population of slums is exposed to open sewage, a cholera outbreak as seen in West Bengal in 1998 would be associated with an incidence of 93,000 cases in 2010 and almost 103,000 cases in 2015 in slum populations. 

However, in looking at the total highly vulnerable population affected by a similar flood in the future, such an outbreak would be only a small part of the potential assistance required to slum populations and those living in extreme poverty.

Potential Shocks:  

[i]  This case study assumes a local shock on the Mumbai area whereby two consecutive extreme precipitation events occur.  Where the first results in mass disruption as seen in July 2005, the second is sufficient to completely overwhelm infrastructure.  Were a synchronous failure to cause the complete breakdown of the megalopolis’s existing water management systems, the incidence of cholera would rise to around 220,000 and 241,000 for 2010 and 2015 respectively, with most of the city exposed to some degree of cholera risk through mains supply contamination. 

Figure 21:  Mumbai – High Vulnerability, Total Affected By Flooding 2010-2015

Numbers of affected: The numbers of affected, based upon this case study, include:

[i]   population of Mumbai living in slums in 2010 and 2015 (8.4 million and 9.3 million)  and below poverty line affected by floods (1.6 million and 1.7 million);

[ii]  the population of Mumbai in 2010 (20 million) and in 2015 (21.9 million) will be exposed to a number of simultaneous effects of severe flooding

[iii] total affected by epidemics linked to floods and infrastructure collapse (220,000 to 241,000)