I have been on my second teaching prac for a month and thus have not had time to keep this updated.
I overestimated the expected inflow from the good rain that we received in August. As of 19 September, we are only up to about 38,000 megalitres of inflow from yearly rain totalling close to 340 mm. Below average rainfall so far for this year and below average inflow. It does not appear that last year's huge amount of rain changed the dynamics significantly: megalitres per mm has dropped to 113.
La Nina has rolled in officially, so it is probable that we will get some good rain over the remaining four months of the year. We need it to push as to the average or above. I admit that I am concerned that we could be heading into another period of drought. At least our dams are full, though.
Monday, September 19, 2011
Thursday, August 18, 2011
August Rain
We had some great rain yesterday: 34.2 mm. This brings the yearly total to around 320 mm, which is still below average for the year. However, we are heading into spring and if ENSO conditions remain neutral or extend to a La Nina we could catch up.
Inflow total thus far is 37,500 megalitres, well below average. There should still be around 3,000 to come from this good rain, but even so we are looking at getting less than 75,000 megalitres of inflow for the year. While this is way better than some recent years, it would be a significant drop on last year. Further, the ratio for inflow to rainfall is 120 megalitres of inflow per mm of rain. This is still a very low ratio, even with last year's very high amount of rain. Remember that the long-term average is 300 megalitres per mm and that inflow declines greater than linearly with decline in rainfall.
This seems to show that the relationship between low rainfall and even lower inflow is still holding. If we get a very bad year or enter drought conditions once more, I would not be surprised to see the inflow to rainfall ratio decline a hell of a lot further in a very short period.
I am still predicting an inevitable collapse of Canberra's water resources that requires urgent action to forestall. However, last year's high rainfall leads me to believe that this will take longer than my initial modelling suggested.
Inflow total thus far is 37,500 megalitres, well below average. There should still be around 3,000 to come from this good rain, but even so we are looking at getting less than 75,000 megalitres of inflow for the year. While this is way better than some recent years, it would be a significant drop on last year. Further, the ratio for inflow to rainfall is 120 megalitres of inflow per mm of rain. This is still a very low ratio, even with last year's very high amount of rain. Remember that the long-term average is 300 megalitres per mm and that inflow declines greater than linearly with decline in rainfall.
This seems to show that the relationship between low rainfall and even lower inflow is still holding. If we get a very bad year or enter drought conditions once more, I would not be surprised to see the inflow to rainfall ratio decline a hell of a lot further in a very short period.
I am still predicting an inevitable collapse of Canberra's water resources that requires urgent action to forestall. However, last year's high rainfall leads me to believe that this will take longer than my initial modelling suggested.
Monday, July 11, 2011
New figures
I am probably going to have to change the way I look at rainfall and runoff to a financial year model, as it seems that that is the main way that ACTEWAGL are reporting data.
However, as of this date we have had 270.6 mm of rainfall for the calendar year and - by a revised calculation that removes the 130 megalitres per day of overflow that ACTEWAGL reported for March and April from my May, June and July figures - 33,000 megalitres of inflow. We have had 23,000 megalitres of water usage over that period also, which is sitting at slightly above last year, but - give the uncertainties - is basically the same.
However, as of this date we have had 270.6 mm of rainfall for the calendar year and - by a revised calculation that removes the 130 megalitres per day of overflow that ACTEWAGL reported for March and April from my May, June and July figures - 33,000 megalitres of inflow. We have had 23,000 megalitres of water usage over that period also, which is sitting at slightly above last year, but - give the uncertainties - is basically the same.
Friday, July 8, 2011
June/July update
I haven't posted for over a month, as I have been elsewhere.
Unfortunately, so has ACTEWAGL's daily usage data while they switched to a new website design ...
This means that I am having to estimate the amount of runoff that we have received. That estimate is currently at around 41,000 megalitres from rainfall of not much more than 280 mm. This estimate is at the high end--we may have received closer to 30,000 megalitres. Rainfall thus far this year has been low, with very low April, May and June. We have already had some rain in July, but it is not yet enough to counter the previous low months. Spring will be all important in determining annual rainfall.
Unfortunately, so has ACTEWAGL's daily usage data while they switched to a new website design ...
This means that I am having to estimate the amount of runoff that we have received. That estimate is currently at around 41,000 megalitres from rainfall of not much more than 280 mm. This estimate is at the high end--we may have received closer to 30,000 megalitres. Rainfall thus far this year has been low, with very low April, May and June. We have already had some rain in July, but it is not yet enough to counter the previous low months. Spring will be all important in determining annual rainfall.
Tuesday, May 31, 2011
Rainfall and runoff: year to date
The last two months have seen low levels of rainfall in Canberra and thus a decline in runoff. However, we have still had 246 mm of rainfall for the year, about average, and runoff of close to 33,000 megalitres.
The runoff total needs to be explained, however, as it is likely that we have had significantly less than this - perhaps as low as 28,000 megalitres. The reason is that I have factored in releases of 130 megalitres a day from Canberra dams over the last month or so. ACTEWAGL were definitely making releases of that magnitude over some of that period, and there were additional releases from smaller dams over one weekend. However, I am pretty certain that these releases stopped a couple of weeks or so ago. To ensure that I overestimate rather than underestimate runoff, I am working on the assumption that releases ceased as of 31 May.
It should be pointed out that even this overestimated runoff total is well below Canberra's average runoff for the first five months of the year. But it is better than last year: at the same point, we had had 21,000 megalitres of runoff.
The runoff total needs to be explained, however, as it is likely that we have had significantly less than this - perhaps as low as 28,000 megalitres. The reason is that I have factored in releases of 130 megalitres a day from Canberra dams over the last month or so. ACTEWAGL were definitely making releases of that magnitude over some of that period, and there were additional releases from smaller dams over one weekend. However, I am pretty certain that these releases stopped a couple of weeks or so ago. To ensure that I overestimate rather than underestimate runoff, I am working on the assumption that releases ceased as of 31 May.
It should be pointed out that even this overestimated runoff total is well below Canberra's average runoff for the first five months of the year. But it is better than last year: at the same point, we had had 21,000 megalitres of runoff.
Thursday, May 19, 2011
Arctic ice volume
I have been doing some work on Arctic sea ice volume, trying to determine whether a second order polynomial function had a physical basis. And I have discovered that it does. While others have obviously already worked this out, it is new to me, and thus at least a little bit exciting. :)
To look at this, what I did was sit and think about what would happen in an Arctic that was melting, and write down a few things.
The first thing that I thought of was that there are two significant parts to the Arctic year - the melt and the freeze. Using the values generated by Frank http://snipt.org/xwgn, I determined that over the period of the model (and, yes, PIOMAS is *not* data, but a model, but it does not matter for the purposes of this exercise) there was an increase in the amount of ice melting each year and a decrease in the amount of ice freezing each year. This increase and decrease were each moving in a linear fashion. It was difficult for me to see how a second order polynomial function could emerge from these linear functions. Silly me, as we will see.
So I set up a model that mirrored these linear changes in melt and freeze, and then looked at the yearly totals at maximum and minimum that resulted. Graphing these totals, I found that the declines in each perfectly followed a second order polynomial function ... What an earth was going on here?
I tried various values for the change constants in both the melt and the freeze periods, but always ended up with second order polynomial functions. So I decided to investigate this function a little more by differentiating it and seeing if the resultant function related in any way to the change constants.
And, of course, it did. What I found was that the differentiated function for the decline in ice volume at the end of the melt season was - with X years - always:
- (Melt Constant + Freeze Constant)* X + (Melt Constant + Freeze Constant)/2
The differentiated function for the decline in ice volume at the end of the freeze season was - with X years - always:
- (Melt Constant + Freeze Constant)* X + (3*Melt Constant + Freeze Constant)/2
Why these particular functions? The constants in them result from the 1/2 years offset between the two seasons. The Melt Constant + Freeze Constant is simply the total yearly change - the two constants added.
So integrating this returns us to our second order polynomial. And why do we integrate? Because the reductions in ice volume in any year are *summed* to the reductions in ice volumes of all previous years. And a sum function is an integral.
In other words, we do not start from scratch each year: each year, we are melting from a lower volume of ice and freezing from a lower volume of ice.
Basically, what it means is that if melting and freezing change in a linear fashion then we get a second order polynomial function for the ice volume totals.
And is there a physical basis for such a linear increase and decrease? Of course: the linear increase in energy, as measured through linear temperature change, in the Arctic due to rising CO2.
Which points to a dramatic crash in Arctic ice volume, and thus area and extent, over the next few years. Indeed, using PIOMAS, further modelling suggests that zero volume will be reached at the end of the melt period in 2018 at the latest, with it occurring possibly as early as 2013.
My projections are:
Year Volume (cubic kilometres)
2011 -> 3744
2012 -> 2853
2013 -> 1935
2014 -> 990
2015 -> 18
2016 -> -981
2017 -> -2007
2018 -> -3060
(all values have a two deviation error range of +/- 2445)
To look at this, what I did was sit and think about what would happen in an Arctic that was melting, and write down a few things.
The first thing that I thought of was that there are two significant parts to the Arctic year - the melt and the freeze. Using the values generated by Frank http://snipt.org/xwgn, I determined that over the period of the model (and, yes, PIOMAS is *not* data, but a model, but it does not matter for the purposes of this exercise) there was an increase in the amount of ice melting each year and a decrease in the amount of ice freezing each year. This increase and decrease were each moving in a linear fashion. It was difficult for me to see how a second order polynomial function could emerge from these linear functions. Silly me, as we will see.
So I set up a model that mirrored these linear changes in melt and freeze, and then looked at the yearly totals at maximum and minimum that resulted. Graphing these totals, I found that the declines in each perfectly followed a second order polynomial function ... What an earth was going on here?
I tried various values for the change constants in both the melt and the freeze periods, but always ended up with second order polynomial functions. So I decided to investigate this function a little more by differentiating it and seeing if the resultant function related in any way to the change constants.
And, of course, it did. What I found was that the differentiated function for the decline in ice volume at the end of the melt season was - with X years - always:
- (Melt Constant + Freeze Constant)* X + (Melt Constant + Freeze Constant)/2
The differentiated function for the decline in ice volume at the end of the freeze season was - with X years - always:
- (Melt Constant + Freeze Constant)* X + (3*Melt Constant + Freeze Constant)/2
Why these particular functions? The constants in them result from the 1/2 years offset between the two seasons. The Melt Constant + Freeze Constant is simply the total yearly change - the two constants added.
So integrating this returns us to our second order polynomial. And why do we integrate? Because the reductions in ice volume in any year are *summed* to the reductions in ice volumes of all previous years. And a sum function is an integral.
In other words, we do not start from scratch each year: each year, we are melting from a lower volume of ice and freezing from a lower volume of ice.
Basically, what it means is that if melting and freezing change in a linear fashion then we get a second order polynomial function for the ice volume totals.
And is there a physical basis for such a linear increase and decrease? Of course: the linear increase in energy, as measured through linear temperature change, in the Arctic due to rising CO2.
Which points to a dramatic crash in Arctic ice volume, and thus area and extent, over the next few years. Indeed, using PIOMAS, further modelling suggests that zero volume will be reached at the end of the melt period in 2018 at the latest, with it occurring possibly as early as 2013.
My projections are:
Year Volume (cubic kilometres)
2011 -> 3744
2012 -> 2853
2013 -> 1935
2014 -> 990
2015 -> 18
2016 -> -981
2017 -> -2007
2018 -> -3060
(all values have a two deviation error range of +/- 2445)
Tuesday, May 10, 2011
Aerosol evolution: two scenarios
This is a post inspired by SteveF's work at Lucia's blog here:
http://rankexploits.com/musings/2011/a-simple-analysis-of-equilibrium-climate-sensitivity/#comment-75758
The above table from excel uses (I hope) SteveF's method to look at the evolution of aerosol forcings over time. In his simple analysis of equilibrium climate sensitivity, SteveF looked at the situation now and worked out what aerosol forcing would have to be if forcing caused an increase of .4207 degrees per watt per square metre and if forcing caused an increase of .81 degrees per square metre (and another higher scenario).
I have extended his analysis to cover the period 1970 to 2010. One of the thing that I noted in the comments to that thread was that the aerosol forcings under the higher sensitivity scenario are currently the same as they were after the Mount Pinatubo eruption. This seems unlikely. More reasonable is the lower sensitivity scenario, in which current sensitivity is about half of that after Mount Pinatubo erupted.
One interesting fact is that under the higher sensitivity scenario there is quite an upward trend over time in aerosol forcings. This does to some extent seem reasonable, imo, as the increase in CO2 emissions is directly associated with an increase in sulphur emissions. In fact, the correlation between well mixed greenhouse gas (WMGHG) forcings is high (r^2 value of 0.81). This makes sense to me.
Still not sure what it all means, but it is interesting to play with. :)
And I have realised that I may have missed one important component: solar forcings. I will check into that.
*Done a little checking. SteveF seems to simply use one value, but that could be because he is only looking at one year - he might change that value for each year.
*Re correlation, the lowest value for a statistically significant correlation, ignoring possible autocorrelation, which is relatively small, is 0.55 degrees per watt per square metre.
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