In article , Michael Percy wrote:
Phred wrote:

In article ,
"Jim Webster" wrote:
it did rather strike me that doing one for an area with five feet of
rain was something of a waste of time.

Each to his own of course, but I know of plenty of places around here
where farmers getting 80 to 100 inches of rain per year still find it
useful to irrigate at times to ensure optimum production of pawpaws,
bananas, and sugar cane.

In contrast the annual deficits would be minimal, guesstimate long term
averages about half an inch or less, for 5' precip areas of the british
isles (from which aspect of practical experience I believe the previous
poster is speaking)

Mind you, I must admit they probably don't decide when or how much by
using a water budget -- more likely kick the ground, look at the sky,
and say "Hmmm... better put on a couple of inches tomorrow." Much as
Gordon says above.

When/if weather data are available it would seem quite outdated not to use
them for waterbudget scheduling of serious irrigation.

Yeah. In fact the local Ag Dept provides at least an "evaporation"
service for broadcast over local radio stations in parallel with other
weather data. But this is really only intended for the irrigation
farmers in the district who get 30 to 40 inches of rain, and an
assured 8-month dry season.

Such are the rainfall gradiants around here, it's only 10 miles from
40 to 60 inch rainfall and *much* better distribution of the latter;
and another 10 miles or so to the 80 inch rainfall of the real "wet
tropics". I don't know of any equivalent evaporation service for
these wetter areas.

I might add that right at the moment a lot of the "wet" country is
actually drought stricken with dairy production down 30% and falling
and the usual "lush green pastures" would be a fire hazard if there
was any fuel left to burn! It's the driest year in over 80 years, or
even since local records began in many places around here.

The whole of eastern Oz is pretty much in the same boat, but the
contrast between "normal" times and the present conditions is more
obvious in places which are usually fairly wet all year every year.

Somewhat ironically, the obligate irrigation farmers here aren't
feeling the pinch as yet (the local dam still has a 12-month supply)
but many of the "opportunists" in the wetter parts who have been
relying on streams and aquifers for their supplementary irrigation
have been banned from pumping until things improve.


Cheers, Phred.

--
LID