Atmospheric moisture budget - Atmosphere, Weather and Climate - page 65

Figure 4.1 The hydrological cycle and water storage of the globe. The exchanges in the cycle are referred to 100 units, which equal
the mean annual global precipitation of 1130 mm. The percentage storage figures for atmospheric and continental water are percentages
of all fresh water. The saline ocean waters make up 97 per cent of all water. The horizontal advection of water vapour indicates the
net transfer.
Source : From More (1967) updated after Korzun (1978).

Table 4.1 Mean water content of the atmosphere
(in mm of rainfall equivalent).

where ∆Q is the time change of moisture in an
atmospheric column, E = evaporation, P = precipitation,
D Q = moisture divergence out of the column, ∆S =
surface storage of water, and r = runoff. For short-term
processes, the water balance of the atmosphere may be
assumed to be in equilibrium; however, over periods of
tens of years, global warming may increase its water
storage capacity.
Because of its large heat capacity, the global occur-
rence and transport of water is closely linked to global
energy. Atmospheric water vapour is responsible for the
bulk of total global energy lost into space by infra-red
radiation. Over 75 per cent of the energy input from the
surface into the atmosphere is a result of the liberation
of latent heat by condensation and, principally, the
production of rainfall.
The average storage of water vapour in the atmos-
phere (Table 4.1), termed the precipitable water content
(about 25 mm), is sufficient for only ten days' supply of

Northern Southern World

hemisphere hemisphere

January 19 25 22

July 34 20 27

Source : After Sutcliffe (1956).

rainfall over the earth as a whole. However, intense
(horizontal) influx of moisture into the air over a given
region makes possible short-term rainfall totals greatly
in excess of 30 mm. The phenomenal record total of
1870 mm fell on the island of Réunion, off Madagascar,
during twenty-four hours in March 1952, and much
greater intensities have been observed over shorter
periods (see E.2a, this chapter).