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Rainfall part 2
Below is a table of rainfall for the
period April 1872 to March 1876, showing
monthly totals.
The table is a good example of how a small
period is far too short for statistical
purposes. The average for the four years is
over double that of the 51 year average in
my original article. It reinforces my point
that March is the most likely month for a
torrential downpour – but note that for two
successive years there was not a drop of
rain in March! The figures for 1874-75 are
much nearer the norm. Note that except for
what was probably one heavy rainfall and one
good shower there was practically no rain
from February 1874 to October 1875
inclusive.
I
have monthly rainfall statistics for
Perim
covering about a 40 year period and one
statistic in the Aden table that is mirrored
for Perim is that there was very
seldom any rain in October.
The main monsoon normally lasted for three
months, beginning in either June or July.
Whereas this monsoon brought much rain at
Dthala, it did not necessarily bring any
rain to Aden (as in 1875).
My final comment is that the year 1872-73
was at the end of an abnormally rainy
quinquennium, such as that mentioned around
1889 in the original article. In due course
I hope to be able to add another monthly
rainfall table or two, which will include at
least one exceptionally dry quinquennium.
I have recently come across some information
on rainfall covering the period 1863-72, in
other words much earlier than that mentioned
in my original article and the period
immediately prior to that covered in the
postscript which includes the Table for
1872-76.
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For Aden the year 1864 was a rainy
one, with a useful amount of rain
falling on four occasions. It didn’t
often rain in the month of February
but in February 1864 there had been
a rainfall that had saturated the
ground well but the quantity had
been only sufficient to fill the
No.1 Tank. In March there was a
decent downpour which filled several
tanks but put only seven feet of
water into the largest tank, the
Coghlan Tank named after a Resident
of the 1850s. |
On 10 May there was a downpour which filled
all tanks to overflowing for the first time
since their refurbishment had been completed
in 1861. It rained again once more about two
weeks later, sufficient to replace what had
been expended in the meantime by
evaporation, usage and leakage. Within about
14 months the tanks would be bone dry.
The rainfall on 24 May 1864 was to be the
last decent amount for another six years.
But then on 27 May 1870 some 7.69 inches of
rain fell in about four hours; however in
the reporting year there was only a further
0.13 inches, which fell in two small
showers.
No.8 Tank (the
‘Coghlan Tank’ as it was called in 1864)
The following year, 1871-72 was a dry one
with only 0.24 inches falling in the year.
From the experience of the 1864 and 1870
storms it was estimated that to fill the
tanks a continuous fall of at least four
inches was required. This to me is
confirmation that the photograph of the
large tank, more or less full, used to
illustrate my original article, was taken in
1929-30, when 3.93 inches fell.
Inglebyj
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