Cities and Water: Sinks or Sponges?


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Cities are usually viewed as sinks; pulling in water resources for domestic and industrial needs. But they can also be seen as sponges as they release water. Usually , however, this is of decreased quality. But if we can make better use of this contaminated water, we can help avert resource crises in the future.

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Cities and Water: Sinks or Sponges?

  1. Cities and Water: Sinks or Sponges? 16th International River Symposium Brisbane, 23 September 2013 Jeremy Bird International Water Management Institute
  2. • More than half of the world’s population lives in urban areas. • Urban growth is most rapid in developing countries: cities gain an average of 5 million residents each month. • There are 23 megacities, compared to 2 in 1970. By 2025, there will be 37. Percentage of urban population and agglomerations by size class, 2011 Percentage of urban population and agglomerations by size class, 2025 Source: United Nations, Department of Economic and Social Affairs, Population Division: World Urbanization Prospects, the 2011 Revision. New York 2012
  3. What is urban? What is rural? Accra: the administrative boundary is outpaced by urban sprawl
  4. Map of population density South Asia exemplifies urbanization challenges and rural-urban tensions
  5. Example: New Delhi 1974 1999 2013
  6. Time for a new approach…. “For most of the last century, economic growth was fuelled by what seemed to be a certain truth: the abundance of natural resources. We mined our way to growth. We burned our way to prosperity. We believed in consumption without consequences. Those days are gone….. Over time, that model is a recipe for national disaster. It is a global suicide pact.” United Nations Secretary General Ban Ki-Moon, World Economic Forum 29th January 2012.
  7. Urban unit • Supply infrastructure • Sewage infrastructure Wastewater disposal • Receiving water bodies • Use in irrigated agriculture Water source • River • Groundwater • Reservoir • Rainfall wastewater treatment? Sink and Sponge Source: van Rooijen, D.J.; Biggs, T.W.; Smout, I.; Drechsel, P. 2010. Urban growth, wastewater production and use in irrigated agriculture: A comparative study of Accra, Addis Ababa and Hyderabad. Irrigation and Drainage Systems 24(1-2): 53-64
  8. Urban expansion, Hyderabad, India Source: Wikimedia Commons
  9. Pulling water in from an increasing distance Hyderabad, India Krishna River Himayat Sagar Osman Sagar GW Musi River GW – Ground Water NJS – Nagarjuna Sagar reservoir Hyderabad Waste water irrigation industry Godavari Basin Krishna Basin NJS Musi River P ET Manjira Singur Godavari River water W ater pum ped Waterpumped Source: van Rooijen, D.; Turral, H.; Biggs, T.W. 2005. Sponge city: Water balance of mega-city water use and wastewater use in Hyderabad, India. Irrigation and Drainage 54: 81-91.
  10. Change in water sources to satisfy urban needs Hyderabad Water Supplies and Demands Osman Sagar Himayat Sagar Ground Water Singur Manjira Krishna river Godavari extra needed (demand - total supply) 0 10 20 30 40 50 60 70 80 90 100 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030 time (years) MillionCubicMetersperMonth Source: Van Rooijen et al., 2005
  11. Informal water markets on the increase • No Indian city has a 24/7 water supply. • Demand for tanker supply on the increase. • Most affected are peri-urban areas where groundwater tables are dropping. Photo by Akshay Davis
  12. Groundwater extraction in India: Urban needs add to existing stress from agricultural use
  13. Examples of water transfers exist …as allocation to agriculture reduced and transferred to urban use Agricultural production levels maintained…
  14. Reflections : Cities as a water sink • Footprint of urban expansion on water for irrigation can be extensive - depends on water source (surface water – groundwater; basin diversion, etc.) and response measures to incentivize water productivity gains – cities like Chennai and examples from China show a major impact on peri-urban water needs. • Rapidly urbanizing cities need a shift to more pro-active, cross- sectoral planning capacity, e.g: – a broad multi-sector approach: managing water transfers, demand management, rainwater harvesting, conjunctive use, etc. – explore downstream irrigation opportunities from a more continuous supply of wastewater and increased storm runoff – promote health safeguards for wastewater re-use
  15. What happens to the urban ‘return’ flow? Urban unit Wastewater disposal Water source wastewater treatment?
  16. In most cities in sub-Saharan Africa, S. Asia and SE Asia, population growth has outpaced the development of sanitation infrastructure, making the management of urban waste, human excreta and wastewater ineffective.
  17. Sewer networks collect only a tiny fraction of city wastewater. The few wastewater treatment plants that exist are often overloaded.
  18. This leads to severe water pollution in peri-urban areas
  19. Wastewater Piped water Also an opportunity?
  20. Due to the proximity of markets and lack of refrigerated transport and storage, a whole irrigation sub-sector specialized in perishable exotic vegetables is emerging in and around growing cities.
  21. In the economically important rural–urban interface, it is difficult to find a reliable unpolluted water source.
  22. 0 5 10 15 20 25 30 Diluted wastewater or polluted water Untreated wastewater Groundwater Treated wastewater River Other surface water bodies Rainfed Irrigation canal Open drainage Numberofcities Source: IWMI, RR 127 Global survey of irrigation source in urban and peri-urban areas: In and around three of four cities in the developing world, farmers use polluted irrigation water for the production of high- value crops
  23. Water quality improves over 40 km along the Musi River Hyderabad Sources: IWMI/J. Ensink
  24. IWMI works closely with WHO and FAO on safe wastewater reuse • Assessing the extent of reuse, risks and benefits. • Developing and testing low-cost options for microbial risk reduction (multi-barrier approach from farm to fork). • Supporting international guidelines and capacity building.
  25. • health risk mitigation measures have a RoI of U$4.9 for each dollar invested. Mitigating risks where wastewater treatment remains a challenge
  26. Australia: National target of 30% of wastewater being recycled by 2015 % Source: Marsden Jacob Associates 2012
  27. Reflections II : Cities as sponges • Wastewater reuse can minimize risks of urban areas becoming water sinks and contribute to water needs at basin scale. • Treatment important: 80% of the contamination of India’s surface water is due to the lack of treatment facilities. • Where conventional treatment remains limited, pathogenic risks can be controlled through safer irrigation practices. • Reducing nutrient loss is becoming a major environmental driver of change
  28. Urban food demands and waste generation mirror the same challenges Source: Wikimedia Commons
  29. Source: IWMI !? Import/ Export Livestock Food Food crops and fodder plants Soil nutrients Organic solid waste, sludge & wastewater Controlled and un- controlled disposal Fertilizer Urban pollution and nutrient wasting Peri-urban and rural nutrient mining Production Consumption/ Processing Cities = vast nutrient sinks Challenge: Closing the nutrient loop
  30. Closing the loop is no easy endeavor in the rural-urban context Technical solutions for resource recovery are available, but: • transport costs are high, • too dependent on public subsidies, • projects rarely survive their pilot periods, and • big gaps in business thinking.
  31. Resource Recovery & Reuse (RRR) A research flagship of CGIAR-WLE using a business approach to attract private capital Old challenges require new thinking
  32. New understandings required to close the loop
  33. RRR program for water, nutrient and energy recovery from domestic and agro-industrial waste  Database of 150+ inspiring RRR business cases  Selection of 60 cases for in-depth analysis (see map)  So far 20 promising business models extracted  Feasibility studies of models starting in 9 cities  Business model implementation targeting 5 cities
  34. Example of a business model currently being implemented in Ghana as a Public-Private Partnership: Fecal Sludge Valorization (returning nutrients and reducing pollution) Other options combine biogas and nutrient recovery
  35. Introducing business models to turn waste into an asset • Solid waste and fecal sludge composting in Asia and Africa could save billions of US$ per year, assuming a market for only 25% of the urban organic waste. • Not a new concept, but many pilots not viable or sustainable • Business models for resource recovery & reuse (RRR) target private and public investors and business schools.
  36. Some ‘nexus’ implications Energy reduction in • Water treatment • Chemical fertilizer production and transport Environmental benefits • Reduced pollution of water bodies • Reduced nitrogen and phosphorous demand • Reduced GHG emissions
  37. Addressing water challenges of rapid urbanization • Analysis: expand inter-sectoral perspective at basin scale to include nutrient and carbon emission considerations. • Peri-urban areas: responsive research, policy and development focus required to reflect the rapid pace of urban transformation • Urban management: support to closed loop processes to avoid cities becoming sinks for valuable resources. • Agriculture-sanitation interface: exploit new approaches, win- win solutions and incentive mechanisms. • Agriculture water productivity: innovations needed to release freshwater for other sectors needs – who pays?
  38. Closing the loop