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4. Nature-based Solutions at the City Scale

Nature-based solutions at the city scale comprise blue-green solutions
created to reinforce urban systems and support disaster risk management
(Figure 5).
High temperatures and extreme weather conditions and heavy precipitation
are the most dangerous climatic threats faced by cities. Water cycle is a natural
and dynamic process that continues in the cities. However, the water cycle in
cities operates in a differently than that in the nature (Strom et al, 2013). The
drought and extreme precipitation caused by climate change also affect water
cycle. The built environment in the cities operates as a system that affects local
hydrology and changes climate, hence affecting the frequency and intensity
of hydrometeorological natural threats (World Bank, 2021). The disruption of
natural hydrological network and blue infrastructure in the cities, and covering
permeable surfaces with impermeable materials prevents water from being
absorbed by the soil and interrupts water flows. Changing the natural form
of rivers, reduction of their area, enclosing them in concrete dikes, destroying
the natural vegetation along water banks, changing the natural structure of
overflow areas, and establishing settlements in these areas turn overflows into
disasters.
Urban floods may take many forms. They can happen due to extreme
precipitation in (urban floods caused by precipitation). In the case of extreme
precipitation in the basin hosting the city, surface runoff moves to the city
due to declination (sudden floods). Urban floods may also include river and
lake-based floods, coastal floods and storm surges. Extreme precipitation
is seen more often in cities due to climate change. In the case of extreme
precipitation, precipitation expected annually may reach cities in a few hours.
As the infrastructure systems of cities are not compatible with the changing
climatic conditions today, this water cannot be moved away from the city and
soon turns into flood.

Figure 5: Nature-based solutions at the city scale

31 Journal of Environment, Urbanization and Climate