Wednesday, May 5, 2010

Current rainfall versus inflow

For the year thus far, we have had 260.8 mm of rain, above the average. The indications are that we will get around 700 mm in total this year, assuming past years are a reasonable guide.

We have had 20,704 megalitres of dam inflow thus far this year, although I would add around 2,000 megalitres to that for the rainfall that we have received in recent days. Call it 23,000. This means that I project we will get 65,260 megalitres of inflow this year, much more than last year. However, this would still equate to less than 35 per cent of average annual inflow, showing the dangerous state of our water situation.

To spell out what this means, we used to get about 180,000 megalitres of inflow per year, on average, with an average rainfall of around 630 mm per year. If the year plays out roughly as I expect, we will be getting 10 per cent more rain than that average but only around a third of the average inflow into our dams.

Something is broken in the hyrdological system. It could be the subsurface soil structure; it could be transpiration and evaporation rates; it could be that *where* the rain is falling has shifted. Is it climate change? Yes. Is it going to get worse? Yes.

Take action now, people. If we wait until mid-decade, Canberra will be facing a disastrous water situation.

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