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Climate change and floods

January 21, 2011

My sympathies are extended to all the Australian families affected by these savage floods.

But I want to push the debate on climate change because most of the sources I’ve consulted over the years have discussed more serious flooding as one of the accompaniments of global warming.

On this blog I recommended Bill McKibben’s book Eaarth as the most essential read of 2010. In his preface he wrote:

Much more quickly than we would have guessed in the late 1980s, global warming has dramatically altered, among many other things, hydrological cycles. One of the key facts of the twenty-first century turns out to be that warm air holds more water vapour than cold: in arid areas this means increased evaporation and hence drought. And once that water is in the atmosphere, it will come down, which in moist areas like Vermont means increased deluge and flood.

He adds that this changed hydrology means more rain comes in heavy downpours:

Not gentle rain but damaging gully washers: across the planet, flood damage is increasing by five pecent a year. Data show dramatic increases – 20 percent or more – on the most extreme weather events across the eastern United States, the kind of storms that drop many inches of rain in a single day. Vermont saw three flood emergencies in the 1960s, two in the 1970s, three in the 1980s – and ten in the 1990s and ten so far in the first decade of the new century.

His message: we now live on a planet where warmer air holds more water vapour and hence we have bigger storms.

For Australia this general trend is potentially more damaging. The CSIRO published a paper in November 2007 on the Hydrological Consequences of Climate Change. It made the point:

A feature of Australian hydrology is that it is more highly variable from year to year than on any other continent. The difference between a one year flood and a one in a hundred years flood is larger than anywhere else.” (my emphasis).

Climate change deniers are fond of saying more savage floods and droughts are nothing to with global warming but everything to do with the Southern Oscillation Index (SOI), the indicator of El Nino. The CSIRO, however, argued in this paper that the relationship between the SOI and the Australian climate is changing. They wrote:

The tropical Pacific Ocean has warmed to historically unprecedented levels, and the SOI has dropped to unprecedented levels. There is some evidence that the amplitudes of rainfall variations have increased as a consequence.

The pioneer of climate change science was of course James Hansen, the head of the NASA Goddard Institute for Space Studies. He warned in his book Storms of My Grandchildren (Bloomsbury, 2009):

Global warming does increase the intensity of droughts and heat waves, and thus the area of forest fires. However, because a warmer atmosphere holds more water vapour, global warming must also increase the intensity of the other extreme of the hydrological cycle – meaning heavier rains, more extreme floods, and more intense storms driven by latent heat, including thunderstorms, tornadoes, and tropical storms. I realized that I should have emphasized more strongly that both extremes increase with global warming.

No causal links here, and the science is inconclusive . But savage floods are absolutely consistent with all that has been speculated about and predicted in the context of “mankind’s craziest experiment” of global warming.

2 Comments
  1. john Christie permalink
    January 21, 2011 2:49 pm

    Bob,I agree with you that theter is something unique & strange about or continents relatonship tp the hydrological cycle. It apperas to be even getting more & more stranger as we now see intense periods of drought being replaced by short periods of devastating floods.

  2. Romola Hollywood permalink
    January 22, 2011 11:17 am

    Thank you Bob for writing about this critical issue. I too feel great sympathy for all the people whose homes have been ruined by these floods across Australia, to say nothing of the loss of wildlife, habitat, and our day-to-day infrastructure. Nevertheless, I have been extremely unsettled by the reporting on these catastrophic events. Phrases like ‘once in 100 years’ and ‘once in 200 years’ have the effect of normalising the situation. I believe it’s essential that we are presented with information that enables us to see that the frequency, intensity and duration of floods and droughts is changing. From my perspective and, clearly for our scientists at the CSIRO who look at the data, their theories and predictions are becoming are reality. To me, this is the main story. Thank you for highlighting this so clearly.

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