View report page

6
Willesden Local Board.
The annual average rainfall for London is
about 25 inches. The amount that fell in the three
quarters was just under 12 inches; it was above the
average by 1.18 inches in February and 076 in July,
but much below it in March, April, May and June,
the amount that fell in those months being 1.47
inches, or about one-fourth below the ordinary
amount. There were 27 days on which it fell. In
the fourth quarter the temperature was 1.0 above
the average. October was generally fine and warm,
but there was rain about the middle of the month.
November was cold and dull. The amount of rain
in the quarter was 8.19 inches, above the average
by 1.12 inches; the total rainfall, therefore, for the
year was 20 inches, about five inches less than
usual. A depth of rain of one inch means a fall of
100 tons over each square acre of ground. During
its fall it absorbs various impurities in the air and
so washes and cleanses it. A deficiency of five
inches in the year would consequently mean a
deficiency of 500 tons of rain on each acre; the
enormous amount that represents in our own
district, an area of 4,383 acres, would not be difficult
of calculation. In a district where the water for
drinking and domestic purposes is supplied to each
house from a long distance the amount of rainfall
is practically immaterial as far as storage purposes
are concerned, but it becomes important when the
cleansing of the air and the surface of the ground
is considered, in the amount, the manner of its fall,
and the number of days on which it falls. In
tropical countries, after a long dry season, the first
fall is generally a verv heavy downpour which
washes the ground; if, on the contrary, it falls
gently, as it more generally does in this country,
there is no cleansing of the surface, but any impurities
are more likely to be brought into a state
of activity by the warmth and moisture.