Theoretical Background - Response of Flood Events to Land Use and Climate Change - page 22

the primary channel of a river without dykes or the area between the dykes for a
river with dyke. The capacity of the channel may be exceeded as a result of
excessive flow distribution or ice or debris jams which could block the flow.
According to theoretical background and previous research regarding to flood,
it is widely acknowledged that anthropogenic behaviors affect floods and flood
hazards. Land use change can affect the amount of runoff for a given storm and
the rapidity with which it runs off. Human occupancy of floodplains increases their
vulnerability due to exposure to flood hazards. Dams, levees, and other channel
alterations affect flood characteristics. Increased occupancy of floodplains and
larger floods due to deforestation and urbanization has been attributed also to
increase flood damage. Deforestation and urbanization increase flooding because
they decrease the capacity of the land to absorb rainfall. It is customary to
assume that flood hazards are stationary, i.e., they do not change with time.
Climate change, anthropogenic influences on watersheds or channels, and natural
watershed or channel changes have the potential, however, to change river flood
hazards.
2.6 Climate Change and its Variability in Europe
In the past, destructive flooding maybe caused by only extremely heavy precipita-
tion. Nowadays, less extreme precipitation may lead to a serious floods event [ 42 ].
Therefore, apart from nonclimatic factors that have affected flooding, 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 mete-
orological hazards [ 22 ]. Many investigators believe that climate change is expected
to have substantial impacts on hydrology on global, regional, and local scale [ 43 ,
44 ]; Andréasson et al [ 43 ]; [ 38 - 40 , 40 , 46 ]. There is also strong evidence that rainfall
changes associated to global warming are already taking place on global and
regional scale. The trend was globally positive throughout the twentieth century,
although large areas were characterized by negative trend [ 38 - 40 ]. Since the report
of Intergovernmental Panel on Climate Change [ 47 ] raised this question that ''Has
the climate become more variable or extreme?'' Analyzing trends in climate extreme
parameters have received increasing attention from many researchers in a variety of
climatological and hydrological studies. Several previous studies concerning long-
term climatologically trends have focused on surface air temperature and precipi-
tation. For example, Lettenmaier et al. [ 48 ] analyzed trends in precipitation, over the
continental USA by applying the Mann-Kendall test, the results of his research
showed an increase in precipitation during autumn in a quarter of the entire stations.
Increasing trend in precipitation was reported by some other researchers in Australia
and New Zealand [ 49 , 50 ] and Argentina [ 51 ]. On the other side, decreasing trend in