When it Rains it Pours
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Sometimes years would go by without rain in Aden. But when it did rain the results were often devastating, destroying life and property. The water would stream down the steep mountainsides with such force that all in its path was carried out to sea.
28th December 1842 was one such day. The Political Agent's Office was flooded and made insecure, the commissariat depots collapsed, as did many recently-built houses and shops. It was reported that nine people and 200 donkeys were swept away in the raging torrents.
The Resident, Commander Haines recommended a watercourse to channel future flood waters to Front Bay, a project which the Government eventually approved after its typically slow consideration and communication.
In 1845 work started on the embanking of the water course. However, before it could be completed another deluge occurred on 2nd May 1846, flooding the town, destroying 27 houses and making just as many unsafe. No lives were lost in the flooding but despite futile measures there followed an outbreak of cholera, which claimed five hundred victims, twenty of whom were European. The flooding caused heavy financial loss to the rice and grain merchants whose supplies for the hot season had just been put on store.
There was major flooding in 1859 when the Tawila Tanks overflowed and despite the benefit of the watercourse it was reported a "a mighty stream carried everything before it, men, camels and all into the sea." Presumably they were in the actual watercourse.
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Following is an except from a letter dated 28th May 1870:
"The clouds had been gathering some days, and yesterday about 3 we were visited by a dust storm, followed by heavy rain, which cleared up about 6, only to come on again at 10 with double force. All night we had the most fearful lightning, and really awful claps of thunder, and rain in torrents. Of course not a thing in our house is dry. I slept on the dining-room table, the only dry place. The register of rain-averages, I hear, about 6 ½ inches, which will give you some idea how it came down, accustomed as you are to Bombay rain. It cleared up about 9 a.m.
After breakfast I rode to camp to see the tanks, which are overflowing, and the water has burst through the wall of the lowest tank, called the Parsee's Tank, being their property [leased from government by Cowasjee Dinshaw syndcate]. The long tunnel to the isthmus has four feet of water in it all along. I got through and found the isthmus end quite blocked up with stones and debris, and had to lead my horse over. The small isthmus where the arsenal is is a sheet of water about two feet deep, and tents and things floating about. No gharry can go to camp, as the road is in some places is completely destroyed. The thunder and lightning were really appalling, and the wind and rain beat with such force I thought the house must come down.
The damage among the residences of the natives is very great, falling down in every direction and killing some few persons. One soldier (European) and one stand of arms were struck by lightning at the Point. The sun has not yet made its appearance again, so it is delightfully cool, and I have been out six hours since breakfast........Vegetation is springing up everywhere, and I saw some flowers by the roadside which had grown and blossomed in one night.
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May 29. - The lightning appears to have played strange pranks. It entered at the window of the barrack-room and knocked down a man; it then divided into two streams and struck some arms on either side of the room, running up their barrels, and curiously through two parrot-cages which happened to be over the arms on either side, and finally it made a hole in the wall on both sides and went through. One can see through the wall where it went through, and there are zig-zag marks on the walls and barrels of the muskets. although it made a hole in the bottom of each cage the parrots were not hurt. Sun out again this morning, and we shall soon be hot again."
The 18 year annual average for Crater for the whole period 1 April 1901 to 31 March 1919 was 1.17 inches. Ignoring the four driest and the four rainiest years the median is slightly less at 1.11 inches. From 1924 to Aden becoming a Colony in 1937 there appears to have been only one official rain gauge, and that was at the Hogg Tower on the ridge between Tawahi and Post Office Bay. I have not been able to locate the details for 1927-28 but for the other 12 years the average annual rainfall was 1.39 inches a year. Ignoring the three driest and the three wettest the median works out at 1.2 inches. For the seven driest years out of the 12 the average was less than half the 12-year average.
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From the two example periods given above one might think that the long-term annual average rainfall for Aden was no more than one and a quarter inches a year. But let us look at a different 16 consecutive years from 1 April 1883 to 31 March 1899. The average for Crater was 3.81 inches – about treble the average for the other 30 years! For the first six years of this earlier period the average was 5.42 inches, with no less than 9.12 inches falling in 1889-90. In the early 1890s the Aden community was searching for a reason for such a drastic change in weather pattern – from the incomplete statistics available it would appear there had been a succession of ‘normal’ dry years immediately prior to 1883. With no global warming to blame it on there were many who seriously thought that the culprit was the long-term effect of constructing the Suez Canal!
One can safely say that in years when the annual rainfall exceeded more than an inch or so the total for the year was not achieved by numerous showers but by one or more torrential downpours. It was only after a succession of such storms that the ‘barren rocks of Aden’ turned green for a few days!
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A rhetorical question I have often asked myself is what quantity of rain was required to fill the Tanks in Crater, assuming they were completely empty. I have found no written evidence on this but the photograph of the Large Tank full is one of a set of postcards issued around 1931. Not unexpectedly one finds that the only abnormal year for Crater in the period 1924-37 was 1929-30 when 3.93 inches fell. (0.2 inches fell in 1930-31 and 2.29 inches in 1928-29). The most likely month for heavy rain was March; one possibility is that around two inches fell at the end of March 1929, to be followed by three or more inches in another storm in early April (thus spanning two reporting years). The alternative is that the tanks were entirely filled by one storm, probably in March 1930. Another photograph of the main tank the main tank nearly full appears on postcards on sale over quite a long period, the earliest being on a ‘court’ sized card from around 1899. In 1898-99 some 3.59 inches of rain fell in Crater, the first abnormal year for a while.
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Occasionally there would be a storm in the main monsoon season, which was normally from June to August, but in some years it began up to a month late. ‘Monsoon’ for the Gulf of Aden meant rough seas but seldom any rain in Aden itself. The storms would be in the mountains inland. Dthala, for example averages about 20 inches a year, most of which fall during the monsoon season. Unfortunately I have not been able to find rainfall statistics for 1921-22 and therefore am unable to quantify the amount of rain that fell in the downpour on 20 March 1922!
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I have mentioned that Crater had an official rain gauge for many years (at the Civil Hospital). For most of the period 1883 to 1919 there were also gauges in Steamer Point (at the European General Hospital) and at the dispensary at Sheikh Othman. Quite often more rain fell in Steamer Point than in Crater, or vice-versa, but over a long period one can say that Steamer Point averaged more than Crater. Annual figures for Sheikh Othman were usually a little higher than for Crater and Steamer Point, and in a couple of years significantly higher – all of which points to storms rather than showers being the provider.
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So what is Aden’s average annual rainfall? Looking at the 51 years for which I have statistics between 1879 and 1937 (there being therefore seven gaps) the average for the whole period is 2.07 inches. Knocking off the five driest and the five wettest years (the latter all between April 1884 and March 1891), the median average falls to 1.70 inches a year. I would be interested to hear from anyone who has more modern statistics covering at least 25 years - from what you have read I hope you will agree that a period much shorter than that will not be sufficiently reliable.
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Below is a table of rainfall for the period April 1872 to March 1876, showing monthly totals.
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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.
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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).
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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.
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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.
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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.
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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.