Geoscience Reference
In-Depth Information
Figure 4.14
Rainfall/duration/
frequency plots for daily maximum
rainfalls in respect of a range of stations
from the Jordan desert to an elevation
of 1482 m in the monsoonal Philippines.
Source
: After Rodda (1970); Linsley
et al
.
(1992); Ayoade (1976).
1143
45
Baguio City,
Philippines
1016
40
35
889
762
30
25
635
20
508
381
15
Lagos, Nigeria
Blaenau
Ffestiniog, U.K.
Cleveland, Ohio
Shoeburyness, U.K.
H5 Jordan
254
10
127
5
0
1.001
0
1.1 1.5
2
5
10
20
50 100 200 300 1,000
Return Period (Years)
southwest England is shown in Figure 4.15. The twenty-
four-hour storm had an estimated 150 to 200-year return
period. By comparison, tropical rainstorms have much
higher intensities and shorter recurrence intervals for
comparable totals.
large areas are of the order of 2000 to 2500 mm or
more.
2
The west coast maxima of mid-latitudes associated
with the storm tracks in the westerlies. The precipita-
tion in these areas has a high degree of reliability.
3
The dry areas of the subtropical high-pressure
cells, which include not only many of the world's
major deserts but also vast oceanic expanses. In
the northern hemisphere, the remoteness of the
continental interiors extends these dry conditions
into mid-latitudes. In addition to very low average
annual totals (less than 150 mm), these regions have
considerable year-to-year variability.
3 The world pattern of precipitation
Globally, 79 per cent of total precipitation falls on the
oceans and 21 per cent on land (Figure 4.1). A glance
at the maps of precipitation amount for December to
February and June to August (Figure 4.16) indicates that
the distributions are considerably more complex than
those, for example, of mean temperature (see Figure
3.11). Comparison of Figure 4.17 with the meridional
profile of average precipitation for each latitude (Figure
4.18) brings out the marked longitudinal variations that
are superimposed on the zonal pattern. The zonal pattern
has several significant features:
4
Low precipitation in high latitudes and in winter over
the continental interiors of the northern hemisphere.
This reflects the low vapour content of the extremely
cold air. Most of this precipitation occurs in solid
form.
Figure 4.17 demonstrates why the subtropics do not
appear as particularly dry on the meridional profile
in spite of the known aridity of the subtropical high-
pressure areas (see Chapter 10). In these latitudes, the
eastern sides of the continents receive considerable
rainfall in summer.
1
The 'equatorial' maximum, which is displaced into
the northern hemisphere. This is related primarily
to the converging trade wind systems and monsoon
regimes of the summer hemisphere, particularly in
South Asia and West Africa. Annual totals over
