Building more dams will bring a bigger emissions headache

In mid February, a Coalition draft dams plan was leaked to the media. This plan suggested the potential for an additional 100 dams across Australia to help with water security and flood mitigation as well as provide hydro-power.

While this plan does not officially form part of the Coalition’s environmental strategy, Tony Abbott has thrown his support behind it, suggesting Australia needs to move beyond it’s “extreme greenism” and “dam phobia”.

One aspect of reservoirs that is not widely appreciated is that they are a source of greenhouse gas emissions. This is due to the inundation of land with a storage of organic matter. If the water column is highly oxygenated, the degradation of this organic matter will produce CO2. If there is little available oxygen, methane is produced. Both are greenhouse gases.

To explore this, I combined data on Australian large dams with a recent comprehensive review of reservoir emissions within the science literature.

Initially, I used the global average surface area emission rates for the comparison, but found that the estimates were unrealistically high. This number was more than 860 million tonnes of CO2 annually. This is probably due to the poor quality of Australian soils in general, which in turn reduce productivity and lead to lower than average organic material storage and thus resultant emissions.

Instead, I used the global total emission from reservoirs (upstream only). This comes to 163 million tonnes of CO2 equivalent, of which Australia is currently responsible for 2.1%, or, 3.42 million tonnes of CO2 equivalent.

Within the dam database, 564 large dams are listed. This returns an average of 6069.15 tonnes of CO2 equivalent per dam, annually. Therefore, an additional 100 dams could provide 0.61 million tonnes of CO2 equivalent annually.

To provide some scale; if this sequestration was achieved through tree plantation, the annual yield required to compensate the average greenhouse gas emissions of 100 new dams would be an additional 0.55 million m3 of wood. This translates to more than 15 thousand hectares of plantation.

As this is utilising the same overly optimistic assumptions as that of my analysis of the Coalition’s Direct Action Plan, the real world figure would likely be much higher.

Data on Australian reservoir emissions came from the height of Australia’s recent prolonged drought, where many reservoirs were far from full and thus covered less land. Emissions downstream (that is, degasing water once it has left the reservoir) were not accounted for in the data also. Additionally, no data on greenhouse gas emissions from dam production is included within this analysis.

Lastly, with the potential for these additional dams to support a new “food bowl” in northern Australia, it is likely subtropical and tropical dams will be favoured. A review of the reservoirs studies globally found that tropical reservoirs produced more greenhouse gases than subtropical which in turn produce more greenhouse gases than temperate dams.

This difference has been suggested to be related to water temperatures, which tend to be warmer closer to the equator, which in turn, speed up the process.

For the reasons listed above, the estimate for average emissions from Australian dams derived above can be seen as conservative (it should be noted that boreal dams were the second highest emitters, due to the tendency for organic rich peat land inundation, however this is irrelevant to Australian climates).

Coupling this with my previous analysis of the Coalition’s Direct Action Plan, if this dam plan is implemented, this additional greenhouse gas contribution would require sequestration above the proposed 85 million tonnes of CO2 equivalent.

Due to the El Niño Southern Oscillation, Australia naturally experiences shifts between drier-than- or wetter-than-average years. Generally, though, Australia is an arid country. Climate change due to increasing greenhouse gas forcing is likely to reduce precipitation globally. For this reason, Australia has strong motivations to lead the path of climate change mitigation.

Should the Coalition win the upcoming September election, my previous analysis illustrated the immense scale and thus cost required to implement the Direct Action Plan. The selected path, soil sequestration, is notably less certain scientifically than other methods, such as plantation. This also comes at the expense of removing the price on carbon which in turn can be utilised to provide market based motivations to decouple carbon emissions from industrial activities and economic growth.

It is not unreasonable therefore to raise concerns about the ability of the Direct Action Plan to assist with climate change mitigation.

Alone, the draft dam plan will contribute a comparatively small greenhouse gas contribution. But by building more dams, the Coalition is making its direct action plan even more difficult to implement.

Find the full report here.


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