Geoscience Reference
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with one of the world's largest mean annual totals of
11,990 mm at 1569-m elevation on Mount Waialeale
(Kauai), but land on the lee side suffers correspondingly
accentuated sheltering effects with less than 500 mm
over wide areas. On Hawaii itself, the maximum falls on
the eastern slopes at about 900 m, whereas the 4200-m
summits of Mauna Loa and Mauna Kea, which rise
above the trade wind inversion, receive only 250 to 500
mm. On the Hawaiian island of Oahu, the maximum
precipitation occurs on the western slopes just leeward
of the 850-m summit with respect to the easterly trade
winds. Measurements in the Koolau Mountains, Oahu,
show that the orographic factor is pronounced during
summer, when precipitation is associated with the
easterlies, but in winter, when precipitation is from
cyclonic disturbances, it is more evenly distributed
(Table 11.3).
The Khasi Hills in Assam are an exceptional instance
of the combined effect of relief and surface configu-
ration. Part of the monsoon current from the head of
the Bay of Bengal (see Figure 11.23) is channelled by
the topography towards the high ground, and the sharp
ascent, which follows the convergence of the airstream
in the funnel-shaped lowland to the south, results in
some of the heaviest annual rainfall totals recorded
anywhere. Mawsyuran (1400-m elevation), 16 km west
of the more famous station of Cherrapunji, has a mean
annual total (1941 to 1969) of 12,210 mm and can claim
to be the wettest spot in the world. Cherrapunji (1340 m)
averaged 11,020 mm during the same period; extremes
recorded there include 5690 mm in July and 24,400 mm
in 1974 (see Figure 4.11). However, throughout the
monsoon area, topography plays a secondary role in
determining rainfall distribution to the synoptic activity
and large-scale dynamics.
Really high relief produces major changes in
the main weather characteristics and is best treated as a
special climatic type. In equatorial East Africa, the three
volcanic peaks of Mount Kilimanjaro (5800 m), Mount
Kenya (5200 m) and Ruwenzori (5200 m) nourish
permanent glaciers above 4700 to 5100 m. Annual
precipitation on the summit of Mount Kenya is about
1140 mm, similar to amounts on the plateau to the south,
but on the southern slopes between 2100 and 3000 m,
and on the eastern slopes between about 1400 and 2400
m, totals exceed 2500 mm. Kabete (at an elevation of
1800 m near Nairobi) exhibits many of the features
of tropical highland climates, having a small annual
temperature range (mean monthly temperatures are
Figure 11.55
March rainfall along the southwestern coast of
Africa (Gabon and Angola) associated with warm and cold sea-
surface conditions.
Source
: After Nicholson and Entekhabi; from Nicholson (1989),
reprinted from
Weather
, by permission of the Royal Meteorological
Society (redrawn).
Figure 11.56
The structure of the sea breeze in western
Colombia.
Source
: After Howell and Lopez (1967); from Fairbridge (1967).
