Rainfall Variations

[farmerfred86]

We have the rainfall data for 3 farms going back to 1971 within a 10 mile radius .
Some years the rainfall amounts are similar but often they can be up to 150mm difference. That's a big difference in annual rainfall.
Obviously fluctuations happen over small areas and local weather is not uncommon but it shows the differen challenges face by individual farms.

All of them however show an approximate 5 year cycle of weather from wetter to dryer periods..

 

[Cowmangav]

150 mm variation across what kind of total though? Annual rainfall less than 30 inches ( 750mm) ??

We got 807 mm from October 2015 to January 2016 , and this year October 2016 to January 2017 was 328 mm .

 

[Cowmangav]

My Uncle brought his friends and neighbours to see our farm in August 1976. It was about the only place in the UK still bright green.

 

[holwellcourtfarm]

Must folk don't realise just how much rainfall does vary locally. Dealing with flood events it quickly became apparent that, even in what seems like widespread wet weather, the actual accumulations can easily vary by 50% or more within a mile radius.

Thunderstorm season is worst.

There will be significant variation across even 100 acres unless it is under the heavy influence of a topographic feature e.g.in a "rain shadow".

This is the main reason that EA flood models are barely useful despite costing many thousands each

 

[bovrill]

Up to 150mm difference?
We've had three fold differences here in different years, varying from under 10" to over 30".

And I'd much rather deal with 10 than 30!

 

[bovrill]

Up to 150mm difference?
We've had three fold differences here in different years, varying from under 10" to over 30".

And I'd much rather deal with 10 than 30!

Aha, silly me. I've got the wrong end of the stick here. I'll leave my comment there though, rather than delete it.

Between my gauge, my father's 100 yards away and my brother in law's two miles away, all at the same height, on the same ridge, we can often vary 10mm+ over a storm or overnight rain. Especially in the summer. The difference between the two either side of the yard is the real eye opener sometimes.

 

[farmerfred86]

Well spotted bovril,

I am more interested in the local variation than the annual variation as you've said.
Across the same yard it's quite extreme though!

I had hoped to mix 2 of our local rainfall records to make one bigger record but local variation means the record wouldn't be accurate. Something around a site like a wooded area to the southwest (prevailing wind) creating some orographic lifting could mean that more rain is experienced here than somewhere else... However small the difference....

 

[holwellcourtfarm]

Well spotted bovril,

I am more interested in the local variation than the annual variation as you've said.
Across the same yard it's quite extreme though!

I had hoped to mix 2 of our local rainfall records to make one bigger record but local variation means the record wouldn't be accurate. Something around a site like a wooded area to the southwest (prevailing wind) creating some orographic lifting could mean that more rain is experienced here than somewhere else... However small the difference....

As your last comment hints, to be comparable both rain gauges must be the same distance from the ground, in an open area with no raised obstructions an any side within a around 100 metres and both calibrated. Expect to see significant variation between them though in any rainfall event.

Generally (a big generalization) there is less local rainfall variation in frontal winter rain and much more in drizzle and summer storms.