An integrated framework for analysis of water supply strategies in a developing city - Chennai (India)

This research effort accomplished three goals:

• understanding the dynamics of the recent water crisis,
• extending the model to project the business-as-usual trajectory of Chennai’s water supply
• understanding how the trajectory may be altered by various policies.

The study departed from previous research studies in several respects.

• Firstly, this study explicitly incorporated self-supply via private wells, and private-supply via the tanker market as an integral part of the urban water system.
• Secondly, the research integrated bio-physical and socio-economic behavior at multiple scales: user-scale supply and demand, utility-scale management, and basin-scale water availability and allocation.
• Finally, the study allowed policy-makers to evaluate and compare a wide-range of policy options on an apples-to-apples basis, something that could not be done with existing frameworks.

An integrative theoretical framework and model were developed to address the research goals. The integrated model was calibrated for the historical period 2002-2006 against extensive physical and socio-economic data: groundwater heads, reservoir levels, household survey data in dry and wet years, tanker surveys, and operational statistics collected from the water utility. The calibration run of the model suggested that the 2003-2004 water crisis was precipitated by rational responses of the utility and Chennai consumers to limited reservoir capacity, unreliable inter-state water transfers, and limited capacity of the local aquifer.

The research also explored scenarios of what the city’s water supply may look like in 2025, using reasonable projections of population, land use and income growth. The historical rainfall record was used to generate scenarios of future rainfall. The 2025 model simulation provided two key insights. Firstly, a future drought was likely to at least as severe as the historical one. Increases in water use due to rising populations and incomes more than compensated for any reductions in peri-urban agricultural water extractions caused by to expanding urbanization. Secondly, it was felt that a “dual-quality” approach to urban water supply could address Chennai’s water problems. The dual-quality solution involved relying on centralised high-quality (and cost) supply for drinking, cooking and dishwashing while using lower quality (and cost) self supplied groundwater for other non-potable needs.

The research indicated that several factors contributed to making the dual-quality solution optimal. In the absence of reliable inter-state deliveries and a local perennial source, the longrun marginal cost of utility supply in Chennai was desalination, a very expensive option. Furthermore, a vast majority of consumers already had private wells; so consumers only considered the pumping costs of extracting groundwater from their wells; the capital costs were sunk costs. So, if in order to achieve full-cost recovery, the utility raised its tariffs above the cost of groundwater extraction from wells, rational consumers would switch out of using utility supply except for uses that necessitated high-quality piped water. The model results indicated this outcome would enhance social welfare if some of the revenues generated by higher tariffs were reinvested in rainwater harvesting and recharge management. Importantly, decreasing demand for utility supply within Chennai would “free” up water for supply to the rapidly-growing, underserved suburbs. Thus, the dual-quality solution would result in a system that was more efficient, equitable, sustainable and reliable overall.

Many other cities in the developing world, particularly in South Asia, exhibit characteristics similar to Chennai: high growth, limited access to new water resources, high marginal cost of new supplies, widespread dependence on private wells and consumer willingness to manage multiple qualities of water in the household. This suggests that the insights and solutions developed in Chennai may be extended to other places.

This research study has been sourced here with permission from the author.

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