Home > Environment > Drying out

Drying out

October 9th, 2006

There’s been a lengthy debate in the comments threads of recent posts about whether the dry weather in much of Australia in recent years can be attributed to climate change, or is just another round in the natural cycle. One point that’s emerged is the crucial role of evaporation in exacerbating drought conditions. This was first observed in relation to the 2002 drought. The steady increase in global temperatures, including average temperatures in Australia, means that even when rainfall is at or near the historical average, conditions are drier than before because evaporation rates are higher. When we get a drought, as at present, conditions that would once have been bad are now extreme.

The combined effects of low rainfall and high evaporation are amplified when it comes to runoff, since the amount (net of evaporation) absorbed by the soil does not change much. And land use changes such as the construction of farm dams have reduced the amount of runoff that makes it into streams (these are now being restricted, but it’s often a case of too little too late). It’s not surprising then, as reported by Mark Neal at the RSMG blog, that, in terms of inflows to the River Murray system, 2006 looks set to be the driest year ever recorded.

So far, the effects on flows and allocations of irrigation water have been offset to some extent by accumulated storage, but with a run of dry years, that can’t be sustained. At the end of September 2006, total River Murray
system storage was 3 550 GL or 37 per cent of capacity, which is only half the long-term average for September of 7 000 GL. With winter and early spring being extremely dry, the chance of significant improvement this year is low, given that 60% of inflow typically occurs during July to October.

But if the situation is bad now, imagine the possibilities if the Cap on extractions hadn’t been imposed back in 1994. We would have started with lower storage levels, and there would have been that much less to draw on.

Categories: Environment Tags:
  1. January 6th, 2007 at 09:31 | #1

    I visited this discussion to get some insight into the drought in Australia and had no idea what a hot-button issue this was in terms of whether the drying has been intensified by AGW. As someone who believes and has written that climate change looms as an enormous threat (but would love to be proved wrong), I’d like to offer just a couple of thoughts. Regardless of the AGW signal in the current drought, there is strong consensus that human-sourced emissions are contributing to many of the dramatic climate changes we are seeing throughout the rest of the world. Consequently, whether this drought is an artifact of AGW should be irrelevant to whether Australia should take action on climate change (unless one is prepared to challenge the entire suite of evidence that humans are affecting climate). Second, it is what happens in the US and Asia that will determine whether Australia becomes a victim of global warming, and not what Australians can do to reduce their own emissions. With its world-class scientists, engineers, and Australia, however, could have a huge global impact on the problem through the development on new technologies,market devices, understanding the science, and adaptive measures. To grab that role, however, its scientific and political leadership have to get past the discussion of whether to do anything at all.
    One last point: I simply don’t understand the argument that we’d be better off waiting twenty years to do something because we’d be richer and reducing C02 would be cheaper. We just had a world record year for C02 emissions, and as Socolow at Princeton has pointed out, every year we wait means that much more we have to take out later to stabilize emissions. Moreover, we are almost assuredly heading for a doubling of C02 (uncharted territory for as long as we’ve been a species), and have no idea whether somewhere between now and then we will cross some tipping point at which climate change becomes irreversible (and impoverishes us all).

Comment pages
1 2 3226
Comments are closed.