9 Deforestation and Frequency of Floods in Romania
281
In a hydrographic catchment, upstream actions can influence the downstream
sides. Therefore a better understanding and assessment of the effects of land use
changes on the hydrological regime is of great importance for prediction and mitigation of flood risk as well as for planning and the sustainable development of space
[45]. An example is the impact of the forest on maximum flows that depend on the
different stages of growth, types of species, climate zones, soil types, morphology
and general land management. Changing the precipitation leakage regime at the level
of the natural or anthropogenic catchment area is well detailed and known by specialists in the field. The surface leakage, for example, ranges from about 10% in the
natural mode to 55% in the anthropogenic regime. This increase in surface leakage
occurs in the detriment of the infiltration of water (decreasing from 25% to only
5% in the anthropic environment) as well as the reintroduction in the hydrological
circuit by evapotranspiration (from 40 to 30%) [46]. A consequence of the change
in rainfall is the increase in the frequency of floods.
This represents a hydrological phenomenon that affects increasingly large areas of
land generating economic, cultural and human losses. In recent decades, strong flood
events have been recorded, with the entire European continent and the economies of
many countries suffering significant losses [47–49]. In Europe, floods have become
increasingly worrying for citizens, authorities, insurance companies, and policymakers, given that in the last 15 years the number of people affected by floods in
European river basins has increased from 11 to 64 per decade [50, 51]. European
countries with large floods registered since the 1970s include Romania, the Czech
Republic, the Slovak Republic, the United Kingdom, Germany, Italy and Austria,
Romania being affected by the highest frequency [52].
The most catastrophic floods are generated by high-intensity heavy rains. Due
to deforestation, the occurrence of high-intensity precipitations in mountain areas
often generates a liquid runoff of more than 100–200 mm/24 h, exceeding the soil
absorption capacity and river transport capacity [53]. Between 1950 and 2006, there
were 12 significant flood events in Europe (flash floods and overflows) with a number
of deaths exceeding 100 in each case [54]. The severe floods in Europe, recorded in
the first part of this century, were caused mostly by heavy rainfall. The years 2002
and 2006 have proven to be record years, with major flood events, recorded in six EU
Member States (Austria, Czech Republic, France Germany, Hungary and Romania).
Part of the upward trend in flood damage can be attributed to socio-economic factors
such as population growth, extensive urbanization in flood-prone areas, as well as
changes in land use, such as increasing deforestation and loss of wet or natural areas,
for example through dyke construction, clogging of whales, etc. [55].
Europe is one of the most urbanized continents, with about 75% of its population
settled in urban areas. The report by the European Environment Agency (EEA) in
2012 [56], shows that about one fifth of the European cities with more than 100,000
inhabitants are very vulnerable to floods produced by overflowing rivers and heavy
rain such as “flash floods”. In fact, for decades, urban drainage systems have been
optimized to evacuate quantities of water of a certain size. Taking into account
the trends of climate change and urbanization that have an ascendant course, this
“transport capacity” has already proved to be inadequate in a large number of cities
281
In a hydrographic catchment, upstream actions can influence the downstream
sides. Therefore a better understanding and assessment of the effects of land use
changes on the hydrological regime is of great importance for prediction and mitigation of flood risk as well as for planning and the sustainable development of space
[45]. An example is the impact of the forest on maximum flows that depend on the
different stages of growth, types of species, climate zones, soil types, morphology
and general land management. Changing the precipitation leakage regime at the level
of the natural or anthropogenic catchment area is well detailed and known by specialists in the field. The surface leakage, for example, ranges from about 10% in the
natural mode to 55% in the anthropogenic regime. This increase in surface leakage
occurs in the detriment of the infiltration of water (decreasing from 25% to only
5% in the anthropic environment) as well as the reintroduction in the hydrological
circuit by evapotranspiration (from 40 to 30%) [46]. A consequence of the change
in rainfall is the increase in the frequency of floods.
This represents a hydrological phenomenon that affects increasingly large areas of
land generating economic, cultural and human losses. In recent decades, strong flood
events have been recorded, with the entire European continent and the economies of
many countries suffering significant losses [47–49]. In Europe, floods have become
increasingly worrying for citizens, authorities, insurance companies, and policymakers, given that in the last 15 years the number of people affected by floods in
European river basins has increased from 11 to 64 per decade [50, 51]. European
countries with large floods registered since the 1970s include Romania, the Czech
Republic, the Slovak Republic, the United Kingdom, Germany, Italy and Austria,
Romania being affected by the highest frequency [52].
The most catastrophic floods are generated by high-intensity heavy rains. Due
to deforestation, the occurrence of high-intensity precipitations in mountain areas
often generates a liquid runoff of more than 100–200 mm/24 h, exceeding the soil
absorption capacity and river transport capacity [53]. Between 1950 and 2006, there
were 12 significant flood events in Europe (flash floods and overflows) with a number
of deaths exceeding 100 in each case [54]. The severe floods in Europe, recorded in
the first part of this century, were caused mostly by heavy rainfall. The years 2002
and 2006 have proven to be record years, with major flood events, recorded in six EU
Member States (Austria, Czech Republic, France Germany, Hungary and Romania).
Part of the upward trend in flood damage can be attributed to socio-economic factors
such as population growth, extensive urbanization in flood-prone areas, as well as
changes in land use, such as increasing deforestation and loss of wet or natural areas,
for example through dyke construction, clogging of whales, etc. [55].
Europe is one of the most urbanized continents, with about 75% of its population
settled in urban areas. The report by the European Environment Agency (EEA) in
2012 [56], shows that about one fifth of the European cities with more than 100,000
inhabitants are very vulnerable to floods produced by overflowing rivers and heavy
rain such as “flash floods”. In fact, for decades, urban drainage systems have been
optimized to evacuate quantities of water of a certain size. Taking into account
the trends of climate change and urbanization that have an ascendant course, this
“transport capacity” has already proved to be inadequate in a large number of cities