Talk:Pan evaporation

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Comment from OhanaUnited

User:OhanaUnited wrote... "Pan evaporation article looks great! It got a good picture, links, and best of all references. I would suggest you to expand the article to have broader context, a global perspective. In the sub-section "Decreasing Trend of Pan Evaporation", you can throw out some stats if possible. As for "Relationship to Hydrological Cycle" sub-section, best to summeralize rather than having a long quoation. But a really good start for an article that is created just over a month. OhanaUnited 03:55, 16 April 2007 (UTC)"[reply]

Kgrr 18:04, 16 April 2007 (UTC)[reply]

RE: Decreasing Trend of Pan Evaporation and Relationship to Hydrological Cycle

You can see the correct solutions to these previous unresolved issues at the following address: http://noparadoxes.tripod.com —Preceding unsigned comment added by 189.71.5.157 (talk) 22:49, 23 May 2008 (UTC)[reply]

What about the flaw of the Class A Evaporation Pan in heavy rainfall events?

I've just read the Pan evaporation wiki post and was rather concerned there is no mention of the fundamental flaw with the Class A Evaporation Pan in heavy rainfall events.

I have had a fair amount of experience using the Class A Evap Pan and its resulting data and, unless it is emptied more than once per day, it is all but useless in events of heavy rainfall i.e. >30mm (203mm rain gauge).

The obvious situation is where the evaporation Pan overflows. This is not uncommon and usually occurs when you have >55mm (203mm rain gauge) in a 24hour period.

There is also the less obvious, and therefore more concerning, influence of heavy or intense rainfall causing spuriously high daily totals without obvious overflow.

Extracting the daily rainfall and evaporation readings in areas with heavy rainfall will show that almost without fail, on days with rainfall in excess of 30mm the daily evaporation will be spuriously higher than other days in the same month where conditions more receptive to evaporation prevailed.

As to exactly what causes this it's hard to say but suspected influences include:

When water in the pan rises near the rim, large droplets could theoretically cause a splashing out of water.

Bird cage covers where large water droplets hit the cage and the resulting spray is carried away by wind rather than falling in the pan.

This will most likely not explain the observed global trend of decreasing evaporation rates however differing quality control procedures over the observed record may partly influence this trend. As is stated in the artcle, more focus is being put on evaporation in recent years so it may be that the spuriously high daily totals are now being removed at a greater frequency than they were previously?

Again the Climate Change issue is a detailed one so that's just some thing to think about.

At worst I’d like to see the Class A Evaporation Pan be modified with an overflow reservoir to eliminate the issues of heavy rainfall.

At best I’d prefer to see evaporation measured by simulated observations based on wind speed, humidity and air temperature.

At the very least there should be a warning of the possible flaw in Wikipedia.

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