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Comment on Trends, change points & hypotheses by Chief Hydrologist

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@webby

I said I would be friends. We have been fitting floods to pdf’s for a long time. It is a similar process. It is used for calculating 1,000 or 10,000 year floods – where data doesn’t exist. You can look up the functions anywhere.

http://s1114.photobucket.com/albums/k538/Chief_Hydrologist/?action=view&current=logpearson.gif

There is no real reason why wind speed should not have a skewed distribution. With complexity , however, we are looking for both extreme events and changes in regime. Extemes are dragon-kings that may not be captured by traditional power distributions. Thus my calculated 10,000 year storm may not be.

The change is regimes is more subtle. In Australia we have 20 to 40 year hydrological regimes in which the average summer rainfall in the wet regime is 4 to 6 times the average in a dry regime. This doesn’t show up in a frequency distribution but is a critical issue for water resources planning for instance. So you can neglect complexity – but in the real world in can bite you hard on the bum.

Robert I Ellison
Chief Hydrologist


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