October 30th 15, 12:23 PM
posted to uk.sci.weather
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First recorded activity by Weather-Banter: Jun 2010
Posts: 5,545
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Ground water
On Friday, October 30, 2015 at 9:06:41 AM UTC, wrote:
"Len Wood" wrote in message
...
On Thursday, 29 October 2015 11:25:16 UTC, wrote:
"Len Wood"
Hi Jim,
If you look at the record of annual rainfall for Plymouth 1874 to 2014
you
see how variable it is with no longterm trend, but clearly trends on
the
decadal timescale.
You can see an increasing trend after the drought of the mid seventies,
and then a decrease and now slight increase again.
I have also put in dropbox the link to the graph of summer and winter
rainfall.
There is a significant increasing trend in winter rainfall and a less
convincing decrease in summer rain. Hence no trend in annual rainfall
over
the longterm.
https://www.dropbox.com/s/u0s7p9kroj...02014.jpg?dl=0
https://www.dropbox.com/s/9lfjie7ko4...0rain.jpg?dl=0
If I was you Jim I would hold fire, but if the water usage has gone up
in
recent years and/or the surface morphology has changed then you are
stuck.
Hi Len, interesting stuff, but I have some questions about the graphs?
1. How consistent was the raingauge site over the years.
My experience of looking at Dartmoor gauges has revealed that just a
small
change in location (even a few hundred metres) can make a statistically
sig.
difference to rainfall. Cowsic is a case in question, due to changes in
aspect from one side of a valley to another.
2. In the 19th Century rainguage height was not consistent, in fact a lot
of
gauges were elevated. Scientifically this was proven to produce lower
rainfalls than rainguages on the ground due to turbulence effects.
In my Dartmoor study I have been very careful to only use data where the
raingauge location has been consistent over the decades and where the
height
of the gauge above ground has been consistent. I think that is important.
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