306
D. Haase
2018). Europe, a continent that became urbanised relatively early, is stagnating in
population growth terms, but cities as such are becoming attractive places to move
to (Scheuer et al. 2016; Wolff et al. 2018). Indeed, land take in and around cities is
not only not subsiding in Europe—it is accelerating. In addition, when considering
the per capita living space increase over the past few decades along with the average
decrease in household sizes in Europe (Haase et al. 2013), land has become a scarce
resource in cities. Recent construction activities are no longer exclusively concentrated on the urban periphery; on the contrary, densification of inner-city areas and
infill development are high on the agenda (Wolff and Haase 2019).
Densification by infill development automatically leads to a decline and a partial
complete disappearance of (spots of) nature in city centres (Haase et al. 2018), despite
the fact that such areas are often high-value nature areas with a rich biodiversity, due
to the wetland and riverine locations of many cities (Kühn et al. 2004). At the same
time, we still find peri-urbanisation and land take outside the city cores on formerly
arable ground, resulting in a decline in fertile land (Nilsson et al. 2014). Thus, the
face of urban growth in European cities is multifaceted and does not include the
considerable percentage of cities and towns in Europe that are shrinking (Wolff et al.
2018).
While growing and densifying, cities also face the direct consequences of ongoing
climate change, such as long-lasting and early heat waves (as the summers of 2018
and 2019 recently demonstrated) including “tropical night” temperatures exceeding
20 °C. This is clearly a challenge for urban public health, in particular for an ageing
urban population in a densely built area (Bosch and Sang 2017). At the same time,
high daytime temperatures and continuous irradiance are a challenge for urban tree
and shrub vegetation, which already suffers from the lack of rainfall. Therefore, heat
has become one of the key challenges for entire urban systems in Europe, including
the environment, public health and the economy, especially when considering cities
that attract (mass) tourism (such as Vienna, Rome and Berlin).
In addition to heat, an increasing risk of flooding in lowland and coastal cities
(Barcelona and Genoa after heavy rainfall, as well as Bosnia, Croatia or Germany
after heavy rainfall and stationary depressions in the past decade) appears to be
another key challenge for European cities (Scheuer et al. 2017). As cities increasingly
accumulate economic value and, of course, human life, the frequency and degree of
hazardous flood events need to be incorporated into a more sustainable and floodproof urban land management (Krysanova et al. 2008). The case of drought and water
shortages is similar, which have recently often alternated with floods: most European
cities are not well prepared for longer-term water shortage and extreme irradiance.
However, cities in Europe are also places of great vestiges of nature (Haase
and Gläser 2009). In addition to the above-mentioned wetlands and riverine land
strips, cities harbour old forests, large parks, numerous gardens and green backyards. Recently, urban green ground infrastructure has been complemented by “vertical green” such as green rooftops and living walls (Pauleit et al. 2018). Moreover,
we know about the positive effects of urban green and blue spaces in cities when
dealing with high air temperatures and irradiance (Weber et al. 2014a). We know the
positive effects of green space for public health and the prevention of heart or lung
D. Haase
2018). Europe, a continent that became urbanised relatively early, is stagnating in
population growth terms, but cities as such are becoming attractive places to move
to (Scheuer et al. 2016; Wolff et al. 2018). Indeed, land take in and around cities is
not only not subsiding in Europe—it is accelerating. In addition, when considering
the per capita living space increase over the past few decades along with the average
decrease in household sizes in Europe (Haase et al. 2013), land has become a scarce
resource in cities. Recent construction activities are no longer exclusively concentrated on the urban periphery; on the contrary, densification of inner-city areas and
infill development are high on the agenda (Wolff and Haase 2019).
Densification by infill development automatically leads to a decline and a partial
complete disappearance of (spots of) nature in city centres (Haase et al. 2018), despite
the fact that such areas are often high-value nature areas with a rich biodiversity, due
to the wetland and riverine locations of many cities (Kühn et al. 2004). At the same
time, we still find peri-urbanisation and land take outside the city cores on formerly
arable ground, resulting in a decline in fertile land (Nilsson et al. 2014). Thus, the
face of urban growth in European cities is multifaceted and does not include the
considerable percentage of cities and towns in Europe that are shrinking (Wolff et al.
2018).
While growing and densifying, cities also face the direct consequences of ongoing
climate change, such as long-lasting and early heat waves (as the summers of 2018
and 2019 recently demonstrated) including “tropical night” temperatures exceeding
20 °C. This is clearly a challenge for urban public health, in particular for an ageing
urban population in a densely built area (Bosch and Sang 2017). At the same time,
high daytime temperatures and continuous irradiance are a challenge for urban tree
and shrub vegetation, which already suffers from the lack of rainfall. Therefore, heat
has become one of the key challenges for entire urban systems in Europe, including
the environment, public health and the economy, especially when considering cities
that attract (mass) tourism (such as Vienna, Rome and Berlin).
In addition to heat, an increasing risk of flooding in lowland and coastal cities
(Barcelona and Genoa after heavy rainfall, as well as Bosnia, Croatia or Germany
after heavy rainfall and stationary depressions in the past decade) appears to be
another key challenge for European cities (Scheuer et al. 2017). As cities increasingly
accumulate economic value and, of course, human life, the frequency and degree of
hazardous flood events need to be incorporated into a more sustainable and floodproof urban land management (Krysanova et al. 2008). The case of drought and water
shortages is similar, which have recently often alternated with floods: most European
cities are not well prepared for longer-term water shortage and extreme irradiance.
However, cities in Europe are also places of great vestiges of nature (Haase
and Gläser 2009). In addition to the above-mentioned wetlands and riverine land
strips, cities harbour old forests, large parks, numerous gardens and green backyards. Recently, urban green ground infrastructure has been complemented by “vertical green” such as green rooftops and living walls (Pauleit et al. 2018). Moreover,
we know about the positive effects of urban green and blue spaces in cities when
dealing with high air temperatures and irradiance (Weber et al. 2014a). We know the
positive effects of green space for public health and the prevention of heart or lung