Geoscience Reference
In-Depth Information
Table 5.4
Flooding events in news reports during June-July 2007
Location (date)
Rainfall or flood statistics
Effect
Midlands and Yorkshire,
1 location 103 mm of rainfall
30,000+ houses affected;
UK (June 2007)
in 24 hours; many places
estimated £1.5bn damage
recorded over 50 mm of rain in
12 hours
New South Wales, Australia
300 mm rainfall in 3 days
9 lives lost, 5,000 evacuated
(June 2007)
Bangladesh (June 2007)
400 mm cumulative rainfall in
130 lives lost, 10,000
places
evacuated
India (June 2007)
475 mm rain in 4 days
57 lives lost, 100,000 people
evacuated
China (June-July 2007)
300 mm rainfall in 4 days
88 lives lost, 500,000 people
evacuated; 56,000 homes
destroyed; 91,800 ha crops
destroyed
Mid-West, USA (July 2007)
305 mm rainfall in 7 days
17 lives lost
Pakistan (July 2007)
105 mm rainfall in 12 hours;
110 lives lost, 200,000
30 year record
homeless
Southern Japan (July 2007)
200 mm rainfall in 4 days
3,400 evacuated
Sudan (July 2007)
At several sites the Nile was 59 lives lost; 30,000 homes
more than a metre higher than in evacuated
1988 (a previous record level)
Northland, New Zealand
270 mm rain total; 213 mm
23 houses destroyed. Estimated
(July 2007)
rain in 24 hours; 1 in 150 year
damage $80M (
≈
US$60M)
storm
Midlands, England, UK
121 mm of rain in 24 hours;
7 people killed, estimated
(July 2007)
wettest May-July since records
£2bn damage
began in 1766
rainfall that has occurred prior to the actual flood-
causing rainfall.
reaches the surface. This will lessen the amount of
rainfall available for soil moisture and therefore the
antecedent soil moisture may be lower under forest
than for an adjoining pasture (NB this is not always
the case, it is dependent on the time of year). The
second factor is that forests often have a high organic
matter in the upper soil layers which, as any
gardener will tell you, is able to absorb more water.
Again this lessens the amount of overland flow,
although it may increase the amount of throughflow.
Finally, the infiltration rates under forest soils are
often higher, leading again to less saturation excess
overland flow.
Deforestation
The effect of trees on runoff has already been
described, particularly with respect to water
resources. There is also considerable evidence that a
large vegetation cover, such as forest, decreases the
severity of flooding. There are several reasons for
this. The first has already been described, in that
trees provide an intercepting layer for rainfall and
therefore slow down the rate at which the water
