Solomon Islands, floods and climate change

I've been saying for a few years now (following Australia's extraordinary run of floods in 2011/12) that more frequent, more damaging floods may well be the first really clear adverse consequence of climate change.

I have been curious to see whether the Solomon Islands devastating floods were the result of clearly exceptional rainfall, especially given that one would expect that an island in the South Pacific would be no stranger to some heavy downpours.

It's been hard to find precise figures for the Solomon Islands event, however.   Several websites referred to "record rainfall", without specifying how much of a record it was.  I think I heard someone on Radio National from the Island claim it was (from memory) much worse than anticipated levels for a 1 in a 100 year flood.  (He also said he had not heard anyone there claim it was due to increased illegal logging.)

The Solomon Islands weather bureau seems to be out of action for any such details, which is hardly surprising.

As for actual figures, I have at last tracked down some:

Around 138m of rain fell in 24 hours on 2 April in Honiara, and a further 318mm fell the next day. The Low Pressure System that caused the rainfall remains in the region and further rain is expected over the next 24 hours.

Not being a meteorologist, how big are those numbers?  Well, in a tropical Queensland context, pretty big.  From a November 2013 news report:

Parts of the north Queensland coast have been lashed by record rainfall with thunderstorms causing flash flooding.

Bowen on Queensland's Burdekin coast officially recorded 267 millimetres overnight.

That is more than double the previous 24 hour rain record for the month of 129 millimetres set in 1950.  Jonty Hall from the weather bureau says much of that came in an hour long deluge.

"Drainage really struggles to cope with that sort of rainfall especially over that period of time," he said.

In the Whitsundays, Hamilton Island registered 233 millimetres - also well up on the previous November record of 145 millimetres in 1991

But in absolute terms, 318 mm is just over a third of the record Queensland daily rain record (an extraordinary 907 mm in 1893, apparently.)   

I wonder what the previous daily record in Solomon Islands is, then.   This site indicates that the average monthly rainfall for March and April are about 350 and 220 mm respectively, which does show that one day of 318mm is a lot.   But in fact, Tully, widely regarded as Australia's wettest town, appears to have a March average rainfall of 752mm. 

So, it does seem that parts of Queensland are, on average, about twice as wet as the Solomon Islands, which is not something I would have expected.

Also, interestingly, this chart which is at a .pdf page you can link to from here, shows a long term trend of decreasing annual rainfall for Honiara:



So, this is another of those cases where climate change is not of uniform consequence everywhere, which scientists have known for a while, but which denialists can't seem to get their head around.  They also can't get their head around the concept of how climate change can mean that a local climate can (as apparently in Honiara's case) be both generally getting drier, but also intermittently be suffering worse floods than ever due to the intensity of rain when it does fall.   (Roy Spencer really jumped the shark with this post.)

But I still don't know how exceptional the rainfall in Honiara recently really has been, for daily local records.

Update:  it looks like the heaviest daily rainfall on at least at one part of Solomon Islands is only 380mm.  I guess the recent rains might still represent a record over a certain number of days, though; and also,  I don't know where Auki station is.