Page 478 - Bahrain Gov Annual Reports (IV)_Neat

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The frequency and depth of irrigation naturally varies with the season and age of the crop.
In practice it is extremely difficult to get labour to water according to a plan and more often
than not, a considerable amount of water is wasted in winter while crops are often insufficiently
watered in summer. It is already clear that careful irrigation is not the general practice and
therefore should merit a good deal of attention from those in charge.
A two-inch irrigation every third day is sufficient for most winter crops. Summer crops
usually need a three-inch irrigation every day, avoiding the late morning and early afternoon for
irrigating. Lucerne is better irrigated to a depth of one inch more than the above figures.
As has been shown earlier the “salts” content of Bahrain’s water is very variable, and in
many cases is too salty (NaCl) or sulphurous to be of any use. The analysis of two typical
samples is shown below.

TABLE 4
No. 1 Sample No. 2 Sample
Temporary Hardness as Ca Co, 200.0 P.P.M. 185 P.P.M.
Permanent Hardness as Ca Co, = 745.0 „ 740 „
Chloride (Na Cl) 2223.0 „ 1850 „
Sulphate (So,) 403.0 „ 500 „
Calcium (Ca) = 272.0 „ 250 „
Magnesium (Mg) 95.0 „ 100 „
Aluminium (Al,0,) 8.0 „ 5 ,
Silica (SiO,) 11.0 45 „
Iron (Fe) 2.0 „ trace
Total solids at 105°C. 4000.0 „ 3400 P.P.M.
pH value = 8.0

III. The Climate
The climate of Bahrain is sub-tropical : it is the practice to grow temperate crops in winter
and tropical crops in summer. High summer temperatures, often reaching 105°F. make deep
irrigations necessary, while in the winter moderate temperatures of 55°F. allow more land to be
cultivated with the available water supply. Average annual rainfall is about 2.9 ins. and falls
mostly from November to March, on perhaps twenty days.

TABLE 5
Average Rainfall, Rainfall per Month
(in inches) (in inches)
1947 .. 3.96 1948 1949
1948 .. 3.67 January 0.05 0.22
1949 .. 3.38 February 0.95 0.36
1950 .. 0.84 March 1.29 0.41
1951 .. 2.44 April 0.66 trace
Av. for 5 years May trace 0.04
2.86 inches November nil 0.28
December 0.72 2.07

Totals 3.67 3.38

It will be seen from the above that there is no consistency as regards rainfall either monthly
or annually. To give a classic example : the annual rainfall in 1946 was 0.15 inches while in
1940 it was 5.53 inches. (It might be mentioned here that the possibility of cloud-seeding has
been investigated, and it was decided that there were insufficient rain-forming clouds to justify
even a full-scale trial, which would necessarily have been expensive. In any event even if
conditions were absolutely perfect, and the maximum “60 per cent, increase in annual rainfall
were obtained, the increase (approximately 1.8 inches) would not justify the expense).