Wednesday, June 16, 2010

Rainfall, runoff and prediction

Rainfall for the year thus far has been 313 mm, and we are expecting some more tomorrow, albeit it a small amount. Thus, we are on track towards 700 mm, but will probably not quite get there.

Runoff, according to my calculations, has been close to 27,750 megalitres. If we did get 700 mm of rainfall this year and if the ratio of runoff to rainfall held, then we would get close to 61,600 megalitres of runoff for the year. I think that we will likely fail to get this amount, and thus maintain my prediction of 60,000 megalitres of runoff.

To put this in perspective, this is about a third of the average runoff that Canberra usually recieves - although when I say 'usually' I mean 'for the period from 1940 to the mid-1990s'. The reason I say that is that our runoff has sharply declined in the last 15 years, as has our rainfall. It will be nice - if temporary, I believe - to get an above average rainfall year.

I would also like to raise one other point in this post. Some people are suggesting that water restrictions can be lifted in Canberra, as we have had lots of rain. However, they fail to take into account two things: the fact that the water restrictions have reduced water consumption in Canberra to around 45,000 megalitres annually and the fact that runoff is not recovering to levels previously comensurate with rainfall. If we are only getting 60,000 megalitres of water in a good rainfall year, it would be madness to remove water restrictions such that our water consumption rose to match that level. If it did, then bad years would be even worse - especially as it takes a year or two to 'train' the population to do what is required when water restrictions have to be reintroduced ...

Wednesday, June 2, 2010

The wager

Willis Eschenbach has made a bet with me regarding ice extent. The proposition is that daily ice extent will fall below one million square kilometres by the end of the 2014 melt season. Willis has the negative; I have the affirmative. The bet is for $US100.

We will use the as our adjudicator, with the final values on 1 November 2014. Obviously, I can win the bet well before then - if sea ice drops below that value on 14 September this year, for example. If Willis wins, he will have to wait for his money until November 2014.

These are the relevant posts from WUWT:

Willis Eschenbach says:

June 1, 2010 at 2:53 am

David Gould says:

June 1, 2010 at 2:15 am

Nigel Harris,

I agree. It is exactly the pattern that we would expect to see. 2007 changed things. It was, indeed, a tipping point (and I know how much that term is loved here. :)). I am one of those alarmists who think that the Arctic will effectively be ice free at the end of the melt period very soon. My specific guess is 2014.

Care to put some money on that prediction? I’m a betting man … a hundred bucks says it won’t go below a million square km of ice by 2014?

And why is it “the pattern that we would expect to see”? Do you know of anyone who predicted it before 2007, anyone who foresaw that we would see a) increasing ice area, combined with b) greatly increased winter ice, and c) greatly reduced summer ice? This is historical revisionism.

Me, I think this new pattern reflects a change in satellites, or a change in procedures, or something like that. But hey, I’ve been wrong before …

1. David Gould says:

June 1, 2010 at 3:09 am

Willis Eschenbach,

No, I know of no specific prediction of this. However, ice cover is a two-dimensional model. Thus, if we have strong melting in the melt period, we would still expect the ice to recover on the surface during winter, and to roughly the same extent as usual – in other words, we would see a strong up and down signal, with more variance between the top and the bottom.

You are correct that there would be no expectation for a higher rebound in winter. That is more likely to be noise over the last couple of years.

As to a bet, $100 sounds fine. I am assuming that you are talking in US dollars.

And which dataset do you want to use? They are all somewhat different in the values that they give, as they all have slightly different procedures. These guys are fine with me. We should wait for corrections, though. I am not sure how long they take, but perhaps the data as presented on that site on 1 November 2014, my time (Australian time)?