Theoretical Background - Response of Flood Events to Land Use and Climate Change - page 21

can be caused by snow obstructing very small channels or ice jams in large rivers.
In the case of rainfall or snowmelt flooding, natural processes can be exacerbated
by watershed changes that enhance runoff production, cause flows to move more
rapidly into the channel, or cause flows to move more slowly or more quickly
within the channel. Thus, deforestation, overgrazing, forest or bush fires, urbani-
zation and obstruction, or modification of drainage channels can be extensive or so
severe as to have a significant effect on flooding.
Tropical cyclones produce hazards from storm surges, to wind and river
flooding. Earthquakes and volcanic eruptions can produce landslides that cause
flooding by damming rivers. Volcanic eruptions are associated with hazardous
mudflows, and volcanic ash may cause flooding by choking river channels. From a
natural hazard perspective, there are important similarities between river flooding;
lake flooding; flooding resulting from poor drainage in areas of low relief; and
flooding caused by storm surges (storm-induced high tides), tsunamis, avalanches,
landslides, and mudflows. All are hazards controlled, to some extent, by the local
topography, and to varying degrees it is possible to determine hazard-prone
locations. Mitigation and relief efforts are also similar [ 22 ].
Although the influence of these causes could be strongly affected by some other
factors, for example, rainfall and sea levels are two major causes of floods, and are
natural and uncontrollable phenomena. However, these natural phenomena which
results in flood damage are very much influenced by human behavior such as:
deforestation in the upper catchment area, straightening of rivers and suppression
of natural flood plains, inadequate drainage practices, and extensive building in
high risk flood areas [ 37 ]. Apart from nonclimatic factors that affect flood events,
there have been adverse flood-hazard changes due to climate change, e.g.,
increasing potential for intense precipitation in the warming world. The scientists
in WMO also believe that there is no doubt, with currently available scientific data,
that climate is changing in the sense of global warming. Global warming, whatever
be the eventual magnitude, will very certainly affect the location, frequency, and
strength of meteorological hazards [ 22 ].
Nonetheless, this research deals with the Ubaye River floods, thus river flooding
will be the focus of this research. Floods along the rivers are natural and an
inevitable part of the resident's life. River Floods depend on precipitation inten-
sity, volume, timing, antecedent conditions of rivers, and their drainage basins
(e.g., presence of snow and ice, soil character, wetness, urbanization, and existence
of dykes, dams, or reservoirs) [ 38 - 40 ]. Some floods occur seasonally with winter
or spring rains; coupled with the melting of snow, the river basins would fill with
too much water too quickly. Torrential rains from decaying hurricanes or tropical
systems can also produce river flooding [ 41 ]. Communications from the com-
mission to the council (the European parliament) report that river floods also may
occur whenever the capacity of the natural or man-made drainage system (such as
dams, dykes) is unable to cope with the volume of water generated by rainfall, or
when flood defenses fail. These are of the most common causes for river flooding
in Europe [ 37 ]. Damaging floods will increase magnitude, when the capacity of the
main conveyance of the river channel is exceeded. The main conveyance may be