Friday, February 26, 2010

The February Storm

On the weekend of the 13 and 14 February, Canberra enjoyed heavy rainfall, with 107.4 mm falling in the space of 50 hours or so.

Since then, I have been tracking inflows into Canberra dams to see how it compares with past inflows.

Today, I believe we have gained the vast majority of that inflow - we might get another 50 megalitres or so over the next couple of days, but probably not that even that much.

From this 107.4 mm of rainfall, Canberra dams received 8,756.6 megalitres of water. By comparison, from the 442.4 mm of rainfall in 2009, Canberra dams recieved 43,240 megalitres of water. This was a terrible year for inflows: 23 per cent of the long-term average.

However, if we recieve the same amount of rain this year as we did last year, and the inflow from that rainfall matches in a megalitre per millimetre sense what went into Canberra dams from the February storm, the percentage would drop below 20 per cent to 19.2 per cent.

Now, this storm was at the tail end of summer, so it can be assumed that the ground was thirsty for water. It may also be the case that big storms provide a lower level of inflow than smaller yet more frequent bursts. However, at this point, the storm has not provided much reason to be hopeful about the future of inflows in Canberra.

It of course remains to be seen whether we will get more rain this year than last year - the odds favour it, as currently (because of the storm) we are about 30 mm above average for the year so far. I will continue to track rainfall versus runoff for the course of this year to see if I can work out any patterns (unlikely from a year of data, but if they are strong they might show up.)

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