Global Population Growth and Water Scarcity Q&A

by Upmanu Lall | August 4, 2010

Russell Sticklor with the Wilson Center’s Environmental Change and Security Program in Washington, DC. recently contacted me requesting my thoughts on a number of issues for an article he is writing on global population growth and water scarcity for the magazine, Outdoor America. I thought some of the comments might be interesting to our blog readers. Watch for the published article as well.

In what ways does land-cover change (urban, agricultural) impact hydrologic cycles, especially as they relate to groundwater recharge? Is aquifer compaction (such as the type seen in Las Vegas) an issue that is widespread in communities/societies across the world that are highly groundwater-dependent?



Urbanization, involving extensive conversion of sandy soils to blacktop or concrete, i.e., impermeable surfaces can reduce groundwater recharge locally. The reduction in recharge coupled with pumping could increase drawdowns in the aquifer leading to compaction. Bangkok, Dacca, Mexico City are examples of places that have seen significant compaction due to groundwater pumping. It is not clear that reduced recharge is the main culprit. Most likely it is the extensive local pumping.

Aquifer drawdown and compaction is much more prevalent in areas with high agricultural pumping and sedimentary environments. However, the examples I gave above relate to urban pumping.

A second and potentially more important impact of land cover change is on water quality — both surface and groundwater. Conversion of forest to cropland often brings with it significant increases in Nitrogen and Phosphorous and pesticides in the water bodies. Biological agents such as E Coli also emerge in this situation if livestock are common. Conversion to urban areas can bring the same pollutants, but the list of potential pollutants can increase dramatically to include metals, complex hydrocarbons and also biological agents.

Finally, many people often ask whether conversion of forest to other uses leads to a reduction or increase in the regional water balance. A similar question is asked of conversion from agricultural to urban area. The answer to these questions is typically situation and location dependent. Some factors are rain intensity and frequency, the density of urban vegetation, and soil types. The agri to urban transition in the US is often water neutral since golf courses and gardens with non-native vegetation lead to roughly the same consumptive use as irrigated farmland.

How might current water-use policies/practices at the domestic and global level be changed to foster more sustainable stewardship of water resources? In particular, how can agricultural policies/practices be changed to boost water efficiency?



In general we need a pricing model that promotes efficient use. This usually means some sort of flat charge for some base use proportional to family size or land size such that there is access for the poor and disadvantaged, followed by a progressively increasing per unit use tariff that reflect the cost of developing and maintaining the resource. Metering is essential in this model, and people will be expected to pay for reliability of service, which implies that the income generated has to be used for assuring this reliability.

I would apply the same logic to agricultural and urban use, with the additional statement that we need to augment metering with incentives for conservation instead of subsidies for use. The incentives could promote water conservation through low flow showerheads, drip irrigation, or switching from high to low water use crops or water application technologies. Often, capital needs to convert households or industries or farms to water conservation strategies are a bottleneck. The incentive program needs to target these needs in a way that is verifiable yet simple and easy to execute.



Is population growth in the American Southwest sustainable, given the increasing pressure it is placing on the region’s ground- and surface water supplies? Is it possible that the region has reached its peak carrying capacity in terms of population?

Yes, it is sustainable, provided that suitable choices for the urban landscape are made — low water using gardens, limited lawns, and golf course lawns irrigated with grey water. A corresponding transition from low cash value agriculture to urban areas would be needed to support this story as a growth story. The population density in the region is actually not that high.

Phoenix and Las Vegas stand out as the canaries in the mine that the area has hit peak water. However, they had egregious or luxury use of water for swimming pools, golf courses and the like. Much of this is going or has to go. The area could actually still engage in high cash value, organic agriculture (it is especially well suited for this) and add population.

In the coming decades, which countries will be hit particularly hard by climate change’s effects on water resources?

The consensus is that small island nations are under the greatest threat from sea level rise. Add Bangladesh and similar countries to the list for the same reason. In addition to the flooding threat, the rising sea level will essentially dramatically shrink the fresh water lens that provides the groundwater supply to these places. So, if you have energy to desalinate this is not a big deal, but otherwise this is a big concern. There is an anticipation that the 10 to 30 deg N or S belt will get drier, and this extends to the Middle East, an area that is already quite water constrained. So, those countries will be in trouble. However, in many countries, essentially the densely populated sub-tropical countries, like India and China and Pakistan, population pressures will dominate and create a water crisis or a food crisis as the water and land for growing food will be limited. Of these, I am most optimistic re China.

In your opinion, could desalination one day help defuse the world’s fresh water crisis? What obstacles are preventing desalination technology from being implemented at a mass level?

Yes. The problem is the energy use and cost. The desalination technology will improve to the point that this will not be an issue for coastal areas. For areas in continental interiors a more aggressive wastewater treatment and reuse strategy will be needed.

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