596
Climatic Geomorphology
..... ~
,, "~
J
~~ "~,.--- o
k
Figure 22.11. Annual thunderstorm frequency. Regions with 100 or more thunderstorms per year are
black. The dotted line encompasses regions with more than 50 thunderstorms per year and the dasheddotted line encompasses regions with at least 20 thunderstorms per year (after Lamb, 1972).
orographic effects (Hayden, 1988). In the first case, air convergence and elevation produce
a cloudy strip around the equator. The seasonal variation of this cloud belt gives rise to
monsoon rains, which in Asia develop between June and September, with an average of
seven monsoon depressions per year (Gupta, 1988). Sometimes these rains can last up to 9
days. Cyclones move from east to west and maximum precipitation takes place on islands
or on continental margins, where the land surface is warmed up and topography enhances
air uplift and increases convectivity (Hayden, 1988). In Cilaos, Reunion Island, 1870 mm
rain fell during a single day (Gupta, 1988). Tropical cyclones with winds greater than
116 km/h are called "hurricanes" and in eastern Asia are known as "typhoons." The
orographic effect consists in the rise and condensation of air masses, which generate the
maximum diurnal precipitation during the period of higher sun warming.
Gauging stations in humid tropics are scarce and in general they are located on big
rivers. Consequently, records of great floods are very limited. Recurrence periods of
intense precipitation are much better known, however, and these data can be related to
great floods, by which some approximate values can be available (Gupta, 1988).
Drainage basin hydrology experiences deep modifications in urban zones, mainly due
to the impermeable surfaces of streets and roofs, which increase flood frequency (Leopold,
1968). This urban-related hydrological change affects urban areas when channel and sewer
networks are insufficient for water evacuation. Then flooding of cities occurs, as it
sometimes happens in Kuala Lumpur (Malaysia) and Singapore (Gupta, 1984; 1993).
Bangladesh, former East Pakistan, is the country that has suffered the worst
catastrophic floods in the humid tropics. It is a small and poor country, with an area of
Climatic Geomorphology
..... ~
,, "~
J
~~ "~,.--- o
k
Figure 22.11. Annual thunderstorm frequency. Regions with 100 or more thunderstorms per year are
black. The dotted line encompasses regions with more than 50 thunderstorms per year and the dasheddotted line encompasses regions with at least 20 thunderstorms per year (after Lamb, 1972).
orographic effects (Hayden, 1988). In the first case, air convergence and elevation produce
a cloudy strip around the equator. The seasonal variation of this cloud belt gives rise to
monsoon rains, which in Asia develop between June and September, with an average of
seven monsoon depressions per year (Gupta, 1988). Sometimes these rains can last up to 9
days. Cyclones move from east to west and maximum precipitation takes place on islands
or on continental margins, where the land surface is warmed up and topography enhances
air uplift and increases convectivity (Hayden, 1988). In Cilaos, Reunion Island, 1870 mm
rain fell during a single day (Gupta, 1988). Tropical cyclones with winds greater than
116 km/h are called "hurricanes" and in eastern Asia are known as "typhoons." The
orographic effect consists in the rise and condensation of air masses, which generate the
maximum diurnal precipitation during the period of higher sun warming.
Gauging stations in humid tropics are scarce and in general they are located on big
rivers. Consequently, records of great floods are very limited. Recurrence periods of
intense precipitation are much better known, however, and these data can be related to
great floods, by which some approximate values can be available (Gupta, 1988).
Drainage basin hydrology experiences deep modifications in urban zones, mainly due
to the impermeable surfaces of streets and roofs, which increase flood frequency (Leopold,
1968). This urban-related hydrological change affects urban areas when channel and sewer
networks are insufficient for water evacuation. Then flooding of cities occurs, as it
sometimes happens in Kuala Lumpur (Malaysia) and Singapore (Gupta, 1984; 1993).
Bangladesh, former East Pakistan, is the country that has suffered the worst
catastrophic floods in the humid tropics. It is a small and poor country, with an area of