Diminishing safe water availability is considered to be one of the most serious problems at the global level today. The cost of developing new resources can be high (see page about traditional approaches), especially in arid regions without access to reliable sources. This implies that increasing the amount of regional precipitation is a sufficient goal for an IPR project. However, there are also inherent co-benefits to consider. These are important because they can provide supplemental revenue and provide added value to the community. Several of these co-benefits are listed in the table below:

Of particular interest are the first two entries in the table – waste-water treatment and carbon sequestration. Operational plantations have already been proposed or developed for these specific purposes.  They feature high-density shrub or tree stands optimized for processing wastewater (typically willow, poplar or other fast-growing species that tolerate wet soils, high nutrient loads and transpire significant amounts of moisture).  Cultivars are selected to maximize nutrient uptake, thrive in the given environment, minimize procurement and maintenance costs, and support commercial opportunities. Some commercial plantations are profitable based on the value of the single service or product they provide, even without considering the multiple benefits (and potential revenue streams) associated with a plantation used for IPR.

Waste water treatment

Natural waste-water treatment systems using tree plantations are already well understood and have been developed by utility companies in some areas because they can be very cost effective. Two examples are shown below:

Traditional facilities can be very expensive; for example, a tertiary sewage treatment plant is currently being built near Sacramento for around $2 billion.  While a price comparison for a plantation which could process the same amount of partially treated waste-water (known as effluent) isn’t available yet, one might be developed at a cost of about $150 million (although this value assumes that costs for developing existing plantations will scale directly with size). There are other considerations as well – to treat the same amount of effluent would require around 60,000 acres of land for the trees. Acquiring land near the treatment plant, and obtaining the necessary permits and various other considerations add to the complexity of developing the plantation. However, we expect development and annual operational costs for a plantation will be significantly lower than those for a traditional waste water treatment plant.

For cities near arid regions, the use of partially treated effluent for irrigation of the trees in an IPR project solves two problems simultaneously. In addition to the primary goal of increasing regional precipitation, IPR provides a way to process sewage effluent and storm run-off – eliminating a source of pollution by transforming a waste-stream into a useful resource.

Carbon Sequestration

Many climate change strategies include establishing tree plantations for carbon sequestration. Because the trees naturally remove carbon dioxide (CO2) from the air, they help offset CO2 emissions from industry and other sources. The approach usually proposed only envisions tree growth on the plantation itself, thus limiting the total amount of CO2 sequestered.  An advantage with IPR is that secondary forest growth is established and maintained “downstream” from the plantation.  If the virtuous cycle of simultaneously increasing growth and precipitation is established, then over time the amount of carbon sequestered by the secondary growth can far exceed that of the cultivated plantation. Because of this, the overall impact of an IPR plantation can far exceed what has been proposed for climate-change mitigation, without increasing the cost.

However, because the proposed plantations alter existing ecosystem processes, legitimate concerns have been raised about unintended consequences such as reduced runoff and water yield, soil nutrient depletion, soil salinity and increases in acidity levels (Reference 3 below). Most of these issues, however, are not likely to be problems with IPR for the following reasons:

• IPR plantations will not be developed by converting arable land or natural ecosystems through afforestation. Instead, land selected for IPR plantations would be previously degraded or contaminated from industrial use, neglected due to desertification or otherwise marginalized and currently unsuitable for agriculture or similar applications.

• Degraded soils are not a concern, since soil quality is expected to improve over time as a result of afforestation, waste-stream fertilization and bioremediation (Reference 2 below).

• Irrigation is provided by wastewater that is currently discarded as a liability, so there is no reduction in downstream water availability.

• The plantation would be heavily irrigated, so there should be no increase in salinity due to the upwelling of saline groundwater or intrusion of seawater. In addition, most arid regions with favorable locations for an IPR project typically receive enough precipitation, or are projected to in the future, to periodically flush the soil and reduce salinization.  Conditions would be monitored in order to ensure this does not become an issue.

There is increasing support for climate-change mitigation projects that remove atmospheric CO2. Various programs have been established to help offset emissions from other sources, and can provide funding for projects that achieve the desired goals. For example, if an IPR project was linked to activities within the framework of the California Forest Protocol, forest-based carbon sequestration would represent an additional potential revenue stream.

Economic Considerations for Integrated Solutions:

While initial cost and benefit comparisons that have been made for waste water treatment and carbon sequestration are reasonably favorable for IPR, the real advantage is apparent when realizing that IPR is an integrated solution providing multiple benefits. When expenses are shared across several functional areas, and the potential arises for multiple income streams – the overall value-proposition improves significantly. A more detailed discussion about IPR co-benefits may be found in the original IPR article.

1. McKenzie C (2005) Wastewater reuse conserves water and protects waterways. On Tap. Winter (2005): 46-51

2. Dimitriou I, Aronsson P (2005) Willows for energy and phyotoremediation in Sweden.Unasylva221 (56), 46-50.

3. Trabucco A, Zomer R, Bossio D A, van Straaten O, Verchot L V (2008) Climate change mitigation through afforestation/reforestation:A global analysis of hydrologic impacts with four case studies.  Agriculture, Ecosystems and Environment 126 (2008) 81-97,doi:10.1016/j.agee.2008.01.015