Theoretical Background - Response of Flood Events to Land Use and Climate Change - page 20

affected approximately 20 million people, mostly by destruction of property,
livelihood and infrastructure, and left about 2,000 dead [ 22 ].
Climate change as huge natural variability and long-term persistence phe-
nomenon is realized as an important factor which affects on flood events but make
it difficult to realize any trends in extreme weather events. During recent decades,
flood damages in Europe have increased considerably [ 32 ]. According to previous
investigations which have focused in Europe, in a large part, this increasing trend
in flood hazard can probably be also attributed to human behavior, such as
developing urbanization in flood plains [ 33 ].
2.5 Types and Causes of Flood Events
Lowland flood-prone areas can be found all over the world, along the coasts, in the
river floodplains, and as inland depressions. Generally, they are basically unsuit-
able for development by their nature; sensitive areas with high physical conditions
and environmental value. However, due to their strategic location and/or suitability
for agriculture activities, there is often a tremendous pressure to develop these
areas for various type of land use beneficial purpose. Therefore, a rapid population
growth, significant increase in agricultural exploitation, urbanization, and indus-
trialization may be observed in these lowland and flood-prone areas. Due to this,
Schultz [ 34 ] mentioned that such areas become increasingly vulnerable from
extreme weather conditions that will have their effect on the requirements for any
drainage and flood-hazard management.
Floods include river floods, urban floods, coastal floods, and sewer floods. They
can be caused by meteorological major causes such as; (a) Intense and/or long
lasting precipitation or rainstorms on a small scale which cause flash floods.
According to WMO [ 35 , 36 ], flash floods typically occur by convective precipi-
tation at high intensity, in short duration (less than 2-6 h) and limited aerial extent
(less than 1,000 km 2 ); (b) widespread storms, which are caused by flooding on a
regional scale. For regional flooding, the range of rainfall duration may differ from
several days to a week or, in exceptional cases (in very large watersheds), may be
associated with multiple storms occurring over a period of several months, such as
in the 1993 flood in the Upper Mississippi River basin or the 1998 flood in the
Yangtze River basin. Other meteorological causes of floods may be grouped into
(c) Snowmelt; and (d) Reduced conveyance due to ice jams or landslides broad
categories. Snowmelt floods are the result of three factors. The existence of the
snowpack (aerial extent and depth), its condition (temperature and water content)
and the availability of energy for melting snow. Snowmelt occurs when energy is
added to a snowpack at 0 C. In snow-dominated regions, some of the largest
floods are caused by warm rain falling onto a snowpack at this temperature. In very
large, snow-dominated watersheds, the annual peak flow is nearly always caused
by snowmelt, whereas either snowmelt or rainstorms can cause the annual peak in
small or medium-sized watersheds. In the cold regions, extreme high water stage