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Urbanisation is increasing and today more than a half of the world’s population lives in urban areas. Cities, especially those where urbanisation is un-planned or poorly planned, are increasingly vulnerable to hydro-meteorological hazards such as heat waves and floods. Urban areas tend to degrade the environment, fragmenting and isolating ecosystems, compromising their capacity to provide services. The regulating role of ecosystems in buffering hydro-meteorological hazards and reducing urban vulnerability has not received adequate policy attention until now. Whereas there is a wide body of studies in the specialised biological and ecological literature about particular urban ecosystem features and the impacts of hazards upon people and infrastructures, there is no policy-driven overview looking holistically at the ways in which ecosystem features can be managed by cities to reduce their vulnerability to hazards. Using heat waves and floods as examples, this review article identifies the aggravating factors related to urbanisation, the various regulating ecosystem services that buffer cities from hydro-meteorological impacts as well as the impacts of the hazards on the ecosystem. The review also assesses how different cities have attempted to manage related ecosystem services and draws policy-relevant conclusions.
Heat waves and floods in urban areas: a policy-oriented review
of ecosystem services
Yaella Depietri Fabrice G. Renaud
Giorgos Kallis
Received: 3 June 2011 / Accepted: 28 September 2011 / Published online: 22 October 2011
Integrated Research System for Sustainability Science, United Nations University, and Springer 2011
Abstract Urbanisation is increasing and today more than
a half of the world’s population lives in urban areas. Cities,
especially those where urbanisation is un-planned or poorly
planned, are increasingly vulnerable to hydro-meteorolog-
ical hazards such as heat waves and floods. Urban areas
tend to degrade the environment, fragmenting and isolating
ecosystems, compromising their capacity to provide ser-
vices. The regulating role of ecosystems in buffering
hydro-meteorological hazards and reducing urban vulner-
ability has not received adequate policy attention until
now. Whereas there is a wide body of studies in the
specialised biological and ecological literature about par-
ticular urban ecosystem features and the impacts of hazards
upon people and infrastructures, there is no policy-driven
overview looking holistically at the ways in which eco-
system features can be managed by cities to reduce their
vulnerability to hazards. Using heat waves and floods as
examples, this review article identifies the aggravating
factors related to urbanisation, the various regulating
ecosystem services that buffer cities from hydro-meteoro-
logical impacts as well as the impacts of the hazards on the
ecosystem. The review also assesses how different cities
have attempted to manage related ecosystem services and
draws policy-relevant conclusions.
Keywords Heat waves Floods Ecosystem services
Urban areas Inland water systems Environmental
Nowadays, more than 50% of people live in urban areas
with some 3.5 billion people having settled in cities
throughout the world (UNFPA 2009). This urbanisation
trend continues today and is likely to continue in the
coming decades (UNFPA 2007). As a consequence, large
changes in exposure to natural hazards and vulnerability of
social-ecological systems are taking place in urban areas.
At the local and regional levels, consumption of natural
assets and disruption of ecosystems
by cities have con-
tributed to the modification of the surrounding environ-
ment. Urban development fragments, isolates and degrades
natural habitats and disrupts hydrological systems (Alberti
2005). The occupation of floodplains, land conversion,
deforestation and loss of ecosystems are anthropogenic
factors that contribute to the loss of buffering capacity of
ecosystems to hazards. For instance, the impairment of soil
functions in urban areas causes the loss of water perme-
ability (i.e. soil sealing), which increases the impacts of
Handled by Victor Savage, National University of Singapore,
Y. Depietri (&)G. Kallis
Institut de Cie
`ncia i Tecnologia Ambientals (ICTA),
Universitat Auto
`noma de Barcelona (UAB), ETSE,
QC/3103, 08193 Bellatera, Barcelona, Spain
Y. Depietri F. G. Renaud
United Nations University, Institute for Environment
and Human Security (UNU-EHS), UN Campus,
Hermann-Ehlers-Str. 10, 53113 Bonn, Germany
G. Kallis
´Catalana de Recerca i Estudis Avanc¸ats (ICREA),
Universitat Auto
`noma de Barcelona (UAB), ETSE,
QC/3103, 08193 Bellatera, Barcelona, Spain
Ecosystems are the dynamic complexes of plant, animal, and
microorganism communities and the nonliving environment interact-
ing as a functional unit, including humans (MA 2005, p. 27).
Sustain Sci (2012) 7:95–107
DOI 10.1007/s11625-011-0142-4
potential floods and the likelihood of urban floods. Besides
this, ecosystems can also be affected by hazards that can be
an important determinant of vulnerability when commu-
nities have high dependencies on specific ecosystem ser-
vices in and around cities. Extreme, large-scale weather
events are likely to trigger ecosystem level disturbances,
which may affect the organisation (species composition
and diversity) and the functional attributes of ecosystems
(Parmesan et al. 2000). Overall, ecological effects of
extreme events have been identified as one of the main
gaps of knowledge in community ecology (Agrawal et al.
While there is growing literature on climate change and
vulnerability assessment (Adger 1999; Handmer et al.
1999; O’Brien et al. 2004;Fu
¨ssel and Klein 2006), com-
paratively little of it concerns cities (Kallis 2008) and even
fewer address the importance of urban ecosystem services
¨et al. 2010). There is extended literature on
ecosystem services,
classification and valuation (Costanza
et al. 1997; de-Groot et al. 2002;MA2005; Fisher et al.
2009), but likewise little of it focuses on the contribution of
buffering hydro-meteorological hazards,
and much less in
cities. This gap is covered by the present review. Our
starting point is that there is a large volume of relevant
material in specialised literatures, not least ecology, about
particular components of the urban ecosystem, but no
overarching interdisciplinary and policy-oriented synthesis
targeting disaster risk reduction. To ground our analysis we
focus on two important hazards, especially for European
cities: heat waves and floods.
Section 2presents the conceptual framework we used
for the review. Section 3discusses concepts related to
ecosystem services and urban systems. Sections 4and 5
review heat waves and floods, respectively. Both sections
address the following components of the framework pre-
sented in Fig. 1: a description of the hydro-meteorological
hazard, the aggravating factors related to urbanisation, the
regulating services (e.g. climate regulation, air quality
regulation and water regulation) and the impacts of the
hazard on the ecosystem. Section 5reviews related policy
initiatives for the protection of urban ecosystem services.
The review ends with a concluding discussion and policy
recommendations (Sect. 6).
Conceptual framework
Figure 1provides a conceptual framework for under-
standing the relationships between urban systems, ecosys-
tems and hydro-meteorological hazards. While we
recognise more integrated definitions of urban ecosystems
that include both human and non-human elements in their
inter-relation (e.g. Pickett et al. 2001), for the sake of this
analysis we maintain a distinction between the human
(‘‘urban systems’’) and ecosystem components. As Fig. 1
indicates, urban areas are vulnerable to hydro-meteoro-
logical hazards but ecosystems offer services that can
buffer these potential impacts. However, urbanisation as a
process erodes these ecosystem services, as do hazard
impacts, especially in a context of climate change and
intensifying extremes, as indicated in Fig. 1. Urbanisation
fragments ecosystems, which diminishes their regulating
capacity and increases the vulnerability of urban areas
themselves. As shown in Fig. 1, we are also interested in
the vulnerability of ecosystems to hazards, defined in
relation to the human component, i.e. their capacity to
withstand stresses and maintain important regulating and
other services. The vulnerability of the urban system
derives therefore from the effect of the impacts of the
hydro-meteorological hazard on the ecosystem and on the
urban system combined with the potential role of regulat-
ing services. It is possible to act in different ways to reduce
this vulnerability. Conventionally policy has focussed on
the urban system component in terms of adaptation policies
seeking to reduce the vulnerability of infrastructures or
particular segments of the population to hydro-meteoro-
logical hazards. This article shifts attention instead to
policies that can act on different leverages, such as urban
ecosystem restoration and preservation by protecting
ecosystems themselves from hazards directly (arrow 1 in
Regulating ser vices
Impact (increase in
Fig. 1 Conceptual framework highlighting the relationships between
hydro-meteorological hazards, ecosystems and urban systems
Ecosystem services are the benefits people obtain from the
ecosystem (MA 2005, p. 27).
Hydro-meteorological hazards are processes or phenomena of
atmospheric, hydrological or oceanographic nature that may cause
loss of life, injury or other health impacts, property damage, loss of
livelihoods and services, social and economic disruption, or environ-
mental damage (UNISDR 2009, p. 18).
96 Sustain Sci (2012) 7:95–107
Fig. 1), ecosystems restoration and preservation (arrow 2)
or indirectly by reducing urbanisation pressures (arrow 3).
Urban areas and ecosystem services
An urban area is defined as ‘‘a set of infrastructures, other
structures, and buildings that create an environment to
serve a population living within a relative small and con-
fined geographic area’’ (Albala-Bertrand 2003, p. 75).
Cities can be additionally defined as settlements that are
permanent. The definition of urban areas adopted in
national census varies from country to country. Three main
classifications of localities as urban can be identified
according to: (1) the size of the population (e.g. civic
district which is in general greater than 2,000, 2,500 or
5,000 inhabitants); (2) the proportion of population of a
civic district engaged in agriculture and the predominance
of non-agricultural workers; and (3) administrative, legal
criteria (e.g. type of local government) (2007 United
Nations Demographic Yearbook). Delimitating urban
areas, from a multidisciplinary perspective, is not a
straightforward task (Pelling 2003). The city can be con-
sidered as a single ecosystem or composed of individual
ecosystems: all natural green and blue areas in the city,
including street trees and ponds; seven ‘‘natural ecosys-
tems’’ are identified: street trees, lawns/parks, urban for-
ests, cultivated land, wetlands lakes/sea and streams
(Bolund and Hunhammar 1999). These ecosystems provide
a variety of services including climate regulation, air
purification, water regulation and carbon dioxide (CO
sequestration. For instance, urban green areas can buffer
extreme events such as heat waves and floods by reducing
temperatures, increasing ventilation, storing water and
reducing run-off (EEA 2010b). The Millennium Ecosystem
Assessment (MA) has identified the following classes of
ecosystem services: ‘‘provisioning services such as food
and water; regulating services such as regulation of floods,
drought, land degradation, and disease; supporting services
such as soil formation and nutrient cycling; and cultural
services such as recreational, spiritual, religious and other
nonmaterial benefits’’ (MA 2005, p. 27). The supply of
these services are the result of the functioning of ecosys-
tems, representing the products of processes that occur
within every ecosystem and, because the processes depend
on organisms and the organisms are linked by their inter-
actions, the services themselves are also linked (Fitter et al.
2010). For the sake of this review we focus mainly on
regulating services and the multiple benefits they provide
for the buffering of heat waves and floods in urban areas.
Of all ecosystem services, regulating services are amongst
the least investigated and assessed, and regulating
service indicators are weaker (i.e. low ability to convey
information and data availability) overall than provisioning
service indicators (Layke 2009). The analysis is based on
the classification of ecosystem services proposed by the
MA and the relevant services for each hazard have been
identified. For heat waves we considered: air quality
regulation and climate regulations, while for floods we
analysed water regulation.
Heat waves
Heat waves as a hazard
Heat waves are extreme events associated with particularly
hot sustained temperatures able to produce notable impacts
on human mortality and morbidity, regional economies and
ecosystems (Koppe et al. 2004; Meehl and Tebaldi 2004).
In Europe, heat waves have been the most prominent
hazard with regards to human fatalities in the last 10 years
(EEA 2010a). One well-documented example is the
European 2003 heat wave when more than 70,000 excess
deaths were reported during the summer (EEA 2010a) and
15,000 excess deaths in France alone (Fouillet et al. 2006).
A large precipitation deficit during spring 2003 contributed
to a rapid loss of soil moisture (Ciais et al. 2005; Zaitchik
et al. 2006; Fischer et al. 2007). As a result, the summer
2003 was by far the hottest since 1500 AD in Europe
(Luterbacher et al. 2004), and it seems that heat waves will
become more intense, longer lasting and/or more frequent
in future warmer climates (Meehl and Tebaldi 2004; Luber
and McGeehin 2008).
Urbanisation as an aggravating factor
In urban areas, the impacts of heat waves are aggravated
and the vulnerability of ecosystems and urban communities
are increased (see Fig. 1). Urban development modifies
land surface, leading to the creation of distinct urban
climates (Grimmond et al. 2004). Urbanisation has
quickly transformed ecosystems to infrastructures and
buildings that increase thermal-storage capacity (Luber and
McGeehin 2008). Built up and impervious surfaces are
stronger absorbers and the radiation is then slowly
re-emitted as long-wave radiation that is responsible of
warming up the boundary layer of the atmosphere within
the urban canopy layer (Oke 1988), producing the so called
‘Urban Heat Island’’ (UHI) effect. The UHI effect con-
cerns the magnitude of the difference in temperature
between cities and their surrounding rural regions and the
temperature difference increases with the number of
inhabitants and the building density: in Europe, the maxi-
mum UHI goes from 2 to 12C (Koppe et al. 2004). Due to
this effect, the highest morbidity and mortality associated
Sustain Sci (2012) 7:95–107 97
with extreme heat appear to occur in cities (Clarke 1972).
Harlan et al. (2006) examined the relation among the
microclimate of urban neighbourhoods, population char-
acteristics, thermal environments that regulate microcli-
mates and the resources people have to cope with climate
conditions in Phoenix, AZ. Neighbourhoods with few open
and green spaces, which have been proven to have cooling
functions, contribute to increasing the impacts of heat in
cities. Heat waves’ mortality rates, neighbourhoods’ envi-
ronmental quality and population characteristics are thus
spatially correlated (Harlan et al. 2006).
Climate regulation
As mentioned, temperatures in cities are higher than in the
surroundings, which cause higher impacts of extreme heat
events. Ecosystems in urban areas contribute to reducing
the UHI effect (Bolund and Hunhammar 1999). However,
urban forests, a common term to characterise all of the
vegetation of an urban region (McPherson et al. 1994), play
a particularly important role in regulating climate, energy
and water between the land surface and the atmosphere
(Zaitchik et al. 2006). According to various authors,
greening can cool the environment at least at the local scale
(Oke 1989; Akbari et al. 2001; Bowler et al. 2010), pro-
viding a climate-regulating service that can buffer the
impacts of heat waves. This is because plants and trees
regulate their foliage temperature by evapo-transpiration,
leading to a reduction of the air temperature. In addition,
green vegetation absorbs up to 90% of the photosyntheti-
cally active radiation while reflecting up to 50% of the near
infrared radiation (Braun and Herold 2003), thus absorbing
less heat than built infrastructures. The size of the green
area contributes to the magnitude of the cooling effect,
although it is not clear if there is a minimum size threshold
or if there is a simple linear relationship between these two
factors: on average an urban park would be around 1C
cooler than a non-green site (Bowler et al. 2010). Gomez
et al. (1998) observed that, in green areas, there was a drop
of 2.5C with respect to the city of Valencia (Spain)
maximum temperature. Wong and Yu (2005) observed a
maximum difference of 4.01C between well planted area
and the central business district area of Singapore, while
according to Hamada and Ohta (2010) the temperature
difference between urban and green areas in Nagoya
(Japan) was large in summer and small in winter. The
maximum air temperature difference was 1.9C in July
2007, and the minimum was -0.3C in March 2004.
Renaud and Rebetez (2009) compared open-site and
below-canopy climatic conditions from 14 different sites in
Switzerland during the 11-day August 2003 heat wave.
Maximum temperatures were cooler under the canopy and,
the warmer the temperature, the stronger the impact of the
forest. For maximum temperature, the difference was
higher in deciduous and mixed forests compared to conif-
erous forests. For minimum temperature, in contrast, the
discrepancy was higher in coniferous forests (Renaud and
Rebetez 2009). Similarly it is worth noting that, during heat
wave days, the increase in sensible heat flux is initially
much larger over forests than over grasslands (Teuling
et al. 2010). In the long term, however, grasslands become
the main heat source due to the fact that elevated evapo-
rative cooling accelerates soil moisture depletion (Teuling
et al. 2010).
According to Alexandri and Jones (2008), although
parks manage to lower temperatures within their vicinity,
they are incapable of significantly cool the surrounding
areas where people live. Therefore, the authors suggest
that it would be more effective to place vegetation within
the built space of the urban fabric; thus raised urban tem-
peratures can decrease within the human habitats them-
selves and not only in the detached spaces of parks. For
single trees, evapotranspiration and tree shading are impor-
tant control measures in heat-island mitigation in Tel-
Aviv (Shashua-Bar and Hoffman 2003). According to these
researchers, the cooling effect depends mainly on the
amount and extent of the partial shaded area. For instance
in Athens, during a short exceptionally hot weather period
in 2007, the highest cooling effect of 2.2C was found to be
reached in a street with high tree shaded area and minimal
traffic load (Tsiros 2010). These results imply the passive
cooling potential of shade trees. Akbari et al. (2001) esti-
mated that 20% of the cooling demand of the USA can be
avoided through the implementation of heat island miti-
gation measures for instance by planting trees. In general,
frequentation and use of green spaces could generate
benefits and well being on people, especially during heat
waves periods, and this could be explained by the capacity
of green spaces to provide better thermal comfort
(Lafortezza et al. 2009).
Air quality regulation
Air quality regulation refers to the role ecosystems play in
regulating the gaseous portion of nutrient cycles that affect
atmospheric composition. Air quality plays an important
role during heat waves and can be a source of human ill-
nesses during these extreme events. During a heat wave in
urban areas, hot days are often followed by hot nights
because of the heat island effect. These conditions can
produce a high degree of heat and air pollution stress,
especially for people with cardiovascular and respiratory
disorders (Piver et al. 1999). For instance, in The Nether-
lands, 1,000–1,400 deaths were estimated because of the
hot temperatures that occurred during the 2003 summer
period, and of these, the number of deaths attributable to
98 Sustain Sci (2012) 7:95–107
the ozone (O
) and particular matter (PM
) concentrations
in the period June–August were estimated at around
400–600 deaths (Fischer et al. 2004). In France, the relative
contribution of O
and temperature in the high mortality
during the 2003 heat wave was heterogeneous among cities
(Filleul et al. 2006). For the nine cities considered in their
study, the excess risk of death for an increase of 10 lg/m
in O
level is significant (Filleul et al. 2006). In particular,
between 3 and 17 August 2003, the excess risk of deaths
linked to O
and temperatures together ranged from 10.6%
in Le Havre to 174.7% in Paris, while the contribution of
alone varied, ranging from 2.5% in Bordeaux to 85.3%
in Toulouse (Filleul et al. 2006). In Croatia, a significant
part of excess mortality, during the same period, was
attributed to PM
and O
in the air (Alebic
´et al.
Due to their large leaf areas and their physical properties
trees can act as biological filters. These can remove large
numbers of airborne particles and hence improve the
quality of air in polluted environments (Beckett et al. 1998;
Nowak et al. 2000; Brack 2002; Jim and Chen 2008;
Escobedo and Nowak 2009). In particular, trees can be
effective in reducing the impacts of damaging forms of
particulate pollution such as PM
or gasses such as
sulphur dioxide (SO
), nitrogen oxides (NO
), carbon
monoxide (CO) and CO
, and are effective in reducing O
concentrations in cities (Nowak et al. 2000). The effec-
tiveness of this ecosystem service varies according to plant
species, canopy area, type and characteristics of air pollu-
tants, and local meteorological environment. Larger trees
extract and store more CO
from the atmosphere and their
greater leaf area traps air pollutants, casts shade and
intercepts rainfall run-off (Brack 2002). Uptake happens
mainly through dry deposition, a mechanism by which
gaseous and particulate pollutants are transported to and
absorbed into plants mainly through their surfaces. In urban
areas, districts with more extensive urban trees capture
more pollutants from the air, and this capacity is increased
as trees gradually reach final dimensions (Jim and Chen
2008). In general, the effectiveness of uptake by trees of
particles [5lm is increased if their leaf and bark surfaces
are rough or sticky (Beckett et al. 1998). For smaller par-
ticles the most effective uptake happens in the needles of
conifers. Due to the larger total surface area of needles,
coniferous trees have a larger filtering capacity than trees
with deciduous leaves, with pines (Pinus spp.) capturing
significantly more material than cypresses (Cupresses spp.)
(Beckett et al. 2000). In addition, this capacity is also
greater because the needles are not shed during the winter,
when the air quality is usually worst (Bolund and
Hunhammar 1999). According to Jim and Chen (2008),
most removal occurs in the winter months mainly due to
the higher pollutants concentrations. However, coniferous
trees are also more sensitive to air pollution and deciduous
trees are better at absorbing gasses (Bolund and Hunham-
mar 1999). Veteran trees (i.e. trees that have lived a long
time and are significant elements of the landscape) often
contribute substantially more benefits to society relative to
other (smaller) trees in the landscape (Nowak 2004). For
instance, veteran trees will store, due to their increased
size, larger amounts of carbon in their tissues. Interception
of particles by vegetation seems also to be much greater for
street trees, due to their location in proximity to high road
traffic (Beckett et al. 1998). Trees situated close to a busy
road capture significantly more material, especially larger
particles, than those situated in a rural area (Beckett et al.
1998). In Chile, it has been demonstrated that Santiago’s
urban forests are effective at removing PM
and Nowak 2009). In 1991, trees in the city of Chicago
(11 percent tree cover) removed an estimated 15 metric
tons of CO, 93 tons of SO
, 98 tons of NO
, 210 tons of 0
and 234 tons of PM
(McPherson et al. 1994). Similarly,
the peri-urban vegetation of the Madrid region constitutes a
sink of O
, with evergreen broadleaf and deciduous tree
species removing more atmospheric O
than conifer for-
ests. Nowak et al. (2000) modelled the effects of increased
urban tree cover on O
concentrations (13–15 July 1995)
from Washington, DC (USA), revealing that urban trees
generally reduce O
concentrations in cities.
Jim and Chen (2008) assessed the capability and mone-
tary value of the removal by urban trees of air pollution in
Guangzhou city in South China. The researcher found that
an annual removal of SO
and total suspended par-
ticulates of about 312.03 mg, and the benefits were valued
at RMB 90.19 thousand. Overall, there are few known
studies that analyse differences in urban forest structure and
air pollution removal in sub-regions of a city, and there are
even fewer studies that link a city’s urban forest structure
and socioeconomic activity with site-specific pollution
dynamics through time (Escobedo and Nowak 2009).
Impacts of heat waves on ecosystems in and around
urban areas
As showed in Fig. 1, hydro-meteorological hazards can
also affect ecosystems, such as forests and water systems,
and their services in urban and peri-urban areas. In the
summer 2003, the drought experienced by the vegetation
was worsened by the length of the period with scarce
precipitations and humidity, by the heat during the summer
and the longer duration of the sunshine period (Rebetez
et al. 2006). In the course of a drought, the gradually
decreasing rate of passage of either water vapour or CO
through the stomata, or small pores of the plant, assimila-
tion and growth are observed (Leuzinger et al. 2005). Fires
can also affect vegetation during heat waves or periods of
Sustain Sci (2012) 7:95–107 99
drought. During the 2003 heat waves, small-scale forest
fires were observed all over central Europe and the western
Mediterranean (Fink et al. 2004).
Trees can be directly affected by air pollutants
depending on the types and concentrations. The most
common effects of plant exposure to O
are modifications
of stomata behaviour, which leads to a reduced photosyn-
thesis and an increased respiration. As gas, NO
and SO
damage cuticles and stomata and, most importantly, they
penetrate through stomata and alter tissues. SO
can cause
both acute (e.g. cell plasmolysis) and chronic injury (e.g.
reduced gas exchange, chlorophyll degradation, chloroplast
swelling, and alteration of cellular permeability). As
mentioned above, after a certain threshold is reached trees
can be affected by nutrient stress, reduced photosynthetic
or reproductive rate, predisposed to entomological or
microbial stress, or direct disease induction (Smith 1974).
In the urban context, water bodies and wetlands are often
beneficial for transportation, recreation, dilution and puri-
fication. On the other hand, urbanisation is thought to cause:
‘reduced baseflows, increased frequency and magnitude of
peak discharges, increased sediment loads, impaired water
quality, reduction in channel and floodplain complexity’’
(LeBlanc et al. 1997). Water quality may further deteriorate
to critical values during periods of prolonged low-flow
conditions in combination with high water temperatures. In
the Meuse river basin, which flows through the cities of
Namur and Lie
`ge in Belgium, during the 1976 and 2003 heat
waves, deterioration of water quality by high water tem-
peratures, eutrophication, increased concentrations of major
elements and some metals or metalloids (selenium, nickel
and barium) were measured (van-Vliet and Zwolsman
2008). However, concentrations of nitrate and some heavy
metals with high affinity for adsorption onto suspended
solids (i.e. lead, chrome, mercury and cadmium) decreased,
which also positively affected chemical water quality during
drought (van-Vliet and Zwolsman 2008). Overall eutro-
phication, following hot spells, causes major impacts on the
water system.
During a heat wave event, temperature of lakes can rise
until reaching record temperatures (increase varies between
1 and 3C on average) (Jankowski et al. 2006). Jankowski
et al. (2006) investigated the consequences of the 2003
European heat wave for lake temperature profiles, thermal
stability (i.e. suppressing downward turbulent mixing) and
hypolimnetic oxygen depletion. Warming of water bodies
can restrict lake overturning and lead to anaerobic condi-
tions, thus potentially seriously impacting aquatic ecosys-
tems, leading, in the summer, to the development of
harmful cyanobacterial blooms. Oxygen depletion may
lead to negative ecological consequences such as phos-
phorous dissolution from the sediments leading to internal
loading and algal blooms (Jankowski et al. 2006). Surface
blooms of toxic cyanobacteria in eutrophic lakes may lead
to mass mortalities of fish and birds, and affects cattle, pets,
and humans (Jo
¨hnk et al. 2008). This may have impacts
on recreational activities, fishing and surface water sports.
In sport fisheries, increased water temperature has been
associated with decreased activity and movement to deeper
cooler waters, which reduces fish catches.
Concerning water quantity, most of the studies agree
that wetlands reduce the flow of water in downstream
rivers during dry periods. In fact evapotranspiration from
wetlands is shown to be higher than from other portions of
the catchment during these periods (Bullock and Acreman
2003). For groundwater resources, prolonged heat stress
may lead to lowered water table levels. In urban areas, the
impairment of soils aggravates the magnitude of this
impact because the reduced infiltration reduces the water
table. Lower water table levels were measured in urban
areas (Scalenghe and Marsan 2009).
Floods as a hazard
The European Union Floods Directive defines a flood as a
temporary covering by water of land not normally covered
by water. According to Few et al. (2004), flood disasters
and their mortality impacts are heavily concentrated in
Asia, where there are high population concentrations in
floodplains, such as the Ganges, Brahmaputra, Mekong and
Yangtze basins, and in cyclone-prone coastal regions such
as around the Bay of Bengal and the South China Sea.
Floods affecting urban areas can be either generated locally
or in other locations in the watershed and basin. Urban
areas often generate impacts on watershed-wide ecosys-
tems such as through land use changes and infrastructure
development, which affects watercourses. When dealing
with floods, it is therefore important to consider the role of
ecosystems not only within the urban areas themselves, but
also in the entire landscape of the watershed and the
influences urban areas have on them (PEDRR 2011). These
two scales of analyses are considered in this section with a
focus on urban areas.
Floods are the result of meteorological and hydrological
factors, but anthropogenic modifications can also play a
role in defining the magnitude of the event. Therefore,
floods in urban areas are the result of natural and man-
made factors. Although these influences are very diverse,
they generally tend to aggravate flood hazards by accen-
tuating flood peaks. As a result of different combinations of
factors, urban floods can basically be divided into four
categories: local floods, riverine floods, coastal floods and
flash floods. Floods in urban areas can be attributed to one
100 Sustain Sci (2012) 7:95–107
or a combination of the above types. The main cause of
urban flooding is a severe thunderstorm, which is generally
preceded by a long but moderate rainfall that saturates the
soil. Therefore floods in urban areas are, in general, flash
floods that expand both on impaired surfaces and in sur-
rounding parks and streets (Andjelkovic 2001). Other
causes of urban floods are: ‘‘inadequate land use and
channelization of waterways; failure of the city protection
dikes; inflow from the river during high stages into urban
drainage systems; surcharge due to blockage of drains and
street inlets; soil erosion generating material that clogs
drainage system and inlets; inadequate street cleaning
practice that clogs street inlets’’ (Andjelkovic 2001).
Major destructive flooding events occurred in Europe in
the last few years: floods in the Elbe basin in 2001 that
produced losses of over 20 billion Euros; floods in Italy,
France and the Swiss Alps in 2000 costing around 12 bil-
lion Euros and a series of floods in the UK during summer
2007 accumulating losses of more than 4 billion Euros
(EEA 2010a). Losses as a consequence of floods have
increased in the past decades in Europe. While there is no
evident trend over time in respect to the number of fatal-
ities and observations do not show a clear increase in flood
frequency (Mudelsee et al. 2003), increases in population
and wealth in the affected areas are the main factors con-
tributing to the increase in losses (EEA 2010a).
Impacts of urbanisation on ecosystems
When degraded by a variety of human activities and
changing climatic conditions, hydrologic regimes typically
have increased frequency and severity of flooding, lowered
water tables and reduced groundwater recharge compared
to previous, more ‘‘natural’’ conditions (Cai et al. 2011).
At the river basin level, urbanisation directly affects
catchments hydrology by changes in surface runoff,
groundwater runoff, groundwater levels and water quality.
The introduction of impervious surfaces inhibits infiltration
and reduces surface retention (Packman 1980). Thus the
proportion of storm rainfall that goes to surface runoff is
increased, and the proportion that goes to evapotranspira-
tion, groundwater recharge and base flow is reduced. This
increased surface runoff is combined with an increase in
the speed of response and increased peak discharge, which
can lead to floods (Packman 1980; Nirupama and Simo-
novic 2006). For instance, in the Upper Thames River
watershed in Canada, urban areas have increased to 22% of
the total watershed area in the year 2000 compared to only
10% in 1974, enhancing the risk from river flooding
(Nirupama and Simonovic 2006). On the other hand, in the
Dead Run watershed (14.3 km
) in the Baltimore, MD,
region, the current tree cover is 13.2% with an impervious
cover of 29%. Increasing tree cover in the watershed to
71% is estimated to reduce total runoff in the watershed
by about 5% for the simulation period of the year 2000
(Nowak 2006). Li and Wang (2009) analysed the urban
expansion of St. Charles County, a suburb of St. Louis,
MO, located in the Dardenne Creek watershed. A rapid
increase of urban areas in the watershed took place from
3.4% in 1982 to 27.3% in 2003, and model simulations
suggested an increase in more that 70% in average direct
runoff in the watershed from 1982 to 2003, correlated with
urban expansion.
At the urban scale, more radical changes in surface
characteristics and soil sealing (i.e. the covering of soil for
housing, roads and parking lots, etc.) increase the imper-
meability of soils, drainage and water run-off and lead to
rapid precipitation run-off, flooding, erosion and impervi-
ous surfaces cause: ‘‘local decreases in infiltration, perco-
lation and soil moisture storage, reductions in natural
interception and depression storage and increases in run-
off’’ (Brun and Band 2000). Severe storms may also yield
discharges exceeding the capacity of the sewer system,
causing choking of the flow and increased attenuation in
localised ponding. The soft ground of vegetated areas
allows water to seep through, and the vegetation takes up
water and releases it into the air through evapo-transpira-
tion (Bolund and Hunhammar 1999). Urban sprawl with
moderate to high soil sealing over a large area reduces the
infiltration potential of the soil and increases the flood risk
of urban areas (EEA 2010a). Soil sealing also impacts the
porosity of soils by reducing it or by modifying its pattern,
which reduces water infiltration (Scalenghe and Marsan
2009). In the surroundings of urban areas the amount and
the speed of flooding water that arrives on unsealed sur-
faces are increased and increase the risk of ponding and
erosion (Scalenghe and Marsan 2009). In these areas, when
human population increases with urban sprawl, wetland’s
functions can easily be affected with pollution or recreational
activities (Mitsch and Gosselink 2000). In these conditions,
wetlands can no longer effectively reduce floods, sequester
pollutants or host different biota (Mitsch and Gosselink
2000). Thus wetland value appears to be maximum when
close to the river system and distributed spatially across an
environment that is not dominated either by cities or agri-
culture, but one that balances nature and human aspects
(Mitsch and Gosselink 2000).
Water regulation
The role of forests and soils
On the local scale, forests and forest soils are capable
of reducing runoff generally as the result of enhanced
infiltration and storage capacities. At the river basin scale,
this holds true for small-scale rainfall events in small
Sustain Sci (2012) 7:95–107 101
catchments, which are not directly responsible for severe
flooding in downstream areas (FAO and CIFOR 2005). The
geomorphology of the area and the preceding rainfall seem
to be the two most important factors in determining the
magnitude of the flooding event: the amount of storm flow
is most directly linked to the area in the watershed and
volume of precipitation or snowmelt deposited on the site,
stored or transported to the stream (Eisenbies et al. 2007).
Overall, forests seem not to be able to stop large-scale
floods, which are caused by severe meteorological events
(Eisenbies et al. 2007).
According to the physical properties of soils, some, not
heavily affected by human activities, have a large capacity
to store water, facilitate transfer to groundwater, and pre-
vent and reduce flooding (MA 2005). The initial conditions
of soil saturation in a basin determine the manifestation and
the intensity of a flood event. In conditions of low soil
saturation, water percolates in the soil and flood risk is
diminished (Lahmer et al. 2000). While in conditions of
high soil saturation, additional precipitation is rapidly
transferred to the river through surface runoff or by inter-
flow (Lahmer et al. 2000). When the soil becomes saturated
and loses its ability to store further water, there does not
seem to be any evidence that forests and their soil have a
noticeable effect in regulating floods for the extreme
rainfall conditions that lead to major flooding events
(Balmford et al. 2008). However, evidence indicates that
the key factor linking land use and flood regulation is soil
condition rather than the trees, and that much of the soil
degradation associated with deforestation results from poor
land use practices (e.g. soil compaction during road
building, overgrazing, litter removal, destruction of organic
matter, clean weeding) (Balmford et al. 2008).
The role of wetlands
Wetland, floodplain, lake and reservoir ecosystems play an
important role in the regulation of floods in inland systems
and provide protection from the adverse consequences of
natural hazards to humans, even for urban areas. In par-
ticular, wetlands are significant in altering water cycle and
perform hydrological functions (Bullock and Acreman
2003). Floodplain wetlands reduce or delay floods; on the
other hand most of the studies show that wetlands located
upstream in a watershed tend to be quickly saturated and
increase the risk of flash floods (Bullock and Acreman
2003). If wetlands are too small, functions, such as storage
of floodwater (for mitigation of floods), no longer exist: it
has been assessed that 3–7% of the area of a watershed
in temperate zones should be maintained as wetlands to
provide both adequate flood control and water quality
improvement functions (Mitsch and Gosselink 2000).
Effective control is more often the result of the combined
effect of a series of wetlands within a catchment area
instead of single units. Some authors argue that, to main-
tain the pulse control function of wetlands, a greater
number of wetlands in the upper reaches of a watershed is
preferable to fewer larger wetlands in the lower reaches
[Loucks (1989) cited in Mitsch and Gosselink (2000)].
A modelling effort on flood control suggested the opposite:
the usefulness of wetlands in decreasing flooding increases
with the distance of the wetland downstream [Ogawa and
Male (1986) cited in Mitsch and Gosselink (2000)]. Further
research is therefore needed in order to determine the real
effects of wetlands and their position in the landscape in
terms of buffering urban areas from floods.
Impacts of floods on ecosystem services
While floods provide a series of benefits (e.g. nutrients
deposition), these hazards can also affect ecosystems
especially when the environment has been degraded. For
instance, flooding and submergence are responsible for
major abiotic stresses and, together with water shortage,
salinity and extreme temperatures are the major factors that
determine species distribution (Visser et al. 2003). Overall,
only pioneering species are able to locate in zones close to
the river (Blom and Voesenek 1996), and floods have a
greater impact on plant species during the growing season
(Kozlowski 1997). Plant responses to flooding during the
growing season include: ‘‘injury, inhibition of seed ger-
mination, vegetative growth, and reproductive growth,
changes in plant anatomy, and promotion of early senes-
cence and mortality’’ (Kozlowski 1997). Adaptive strate-
gies and flood tolerance of plants depend on plant species
and genotype, age of plants, frequency, duration, timing
and conditions of flooding (i.e. soil flooding, water logging,
total submergence of vegetation) (Kozlowski 1997;
Vervuren et al. 2003). Underwater light intensity and depth
of the water column may also affect survival during periods
of submergence (Vervuren et al. 2003).
Flooding also changes the physical status of soils, which
may severely affect peri-urban agricultural practices. For
instance, water logging causes the breakdown of large
aggregates into smaller particles, deflocculation of clay
and destruction of cementing agents. As the water level
declines, these small parts of soil are redistributed in a new,
more dense structure, creating: ‘‘smaller soil pore diame-
ters, higher mechanical resistance to root penetration, low
concentrations and the inhibition of resource use’
(Blom and Voesenek 1996) and the accumulation of CO
in soils (Kozlowski 1997). Gas diffusion is severely
inhibited during flooding (Blom and Voesenek 1996):
oxygen remains in the soils and is consumed by aerobic
processes (roots and soil organisms), nutrient availability
for plants strongly decreases and anaerobic processes take
102 Sustain Sci (2012) 7:95–107
place producing toxic substances for plants [lowering of
soil redox potential (Eh)]. Chemical changes also include
the increased solubility of mineral substances, reduction of
Fe, Mn and S, and anaerobic decomposition of organic
matter. The reduction condition (i.e. low soil Eh) is also a
major factor in wetland ecosystems that influences plant
survival, growth and productivity (Pezeshki 2001). Floods
can also cause secondary impacts, for instance affecting
industries and in particular petrochemical ones, causing
the release of toxic chemicals, which further impact the
Policy initiatives for the protection of urban ecosystem
services for disaster risk reduction
At the international level, policy initiatives that target any
of the three points of policy leverage identified in Fig. 1, are
rare. The United Nations International Strategy for Disaster
Reduction’s (UNISDR) Hyogo Framework for Action
2005–2015 lists ‘‘sustainable ecosystems and environmen-
tal management’’ as one of the main pillars for reducing
underlying risk factors (UNISDR 2005). Calling for an
improved management of ecosystems and their services for
disaster risk reduction, this initiative directly targets arrow 2
of the framework in Fig. 1. Paragraph 19 of the Hyogo
Framework can be situated in correspondence to arrow 3 of
the framework as it establishes the Priority for Action 4:
‘Reduce the underlying risk factors’’, which include:
‘Incorporate disaster risk assessments into urban develop-
ment planning and management of disaster-prone human
settlements’‘rural development’‘major infra-
structure’‘including considerations based on social,
economic and environmental impact assessments’’. In
addition the UNISDR campaign on Making Cities Resilient
proposes a 10-point checklist to serve as a guide for com-
mitment by Mayors (UNISDR 2010). Point 8 makes explicit
the need to consider the environmental dimension: ‘‘Protect
ecosystems and natural buffers to mitigate floods, storm
surges and other hazards to which your city may be vul-
nerable. Adapt to climate change by building on good risk
reduction practices’’ (UNISDR 2010,p.9).
At the local and regional levels, policy initiatives are
very few for the incorporation of ecosystem preservation
for disaster risk reduction in urban areas. At the European
level, the Communication from the Commission to the
European Parliament ‘‘Options for an EU vision and target
for biodiversity beyond 2010’’ identifies four policy
options to halt the loss of biodiversity and ecosystem ser-
vices by 2020 but with no reference to disaster risk
reduction (EC 2010). For European countries, notably the
UK, The Netherlands and Germany, affected by severe
flooding in recent years, have made policy shifts to
‘making space for water’’, represented by arrow 2 of the
framework (Fig. 1). New risk management policies and
practices favour a more holistic approach to flood risk
management based on River Basin Management Plans,
Integrated Coastal Zone Management to enhance natural
Regarding heat waves, the London local government
authorities have developed the ‘‘Right Trees for a Changing
Climate’’ database and website to provide advice on
planting the right trees in the right place, based on the fact
that planting more trees, alongside increasing other green
cover, is one of the ways in which London can adapt to
climate change (,
using vegetation to keep the city cool. The city has set
ambitious targets to: increase tree cover by 5% by 2025;
increase greenery in the centre of London by 5% by 2030
and a further 5% by 2050; create 100,000 m
of new green
roofs by 2012; and enhance 280 hectares of green space by
2012. Stuttgart has planned to exploit the role of natural
wind patterns and dense vegetation in reducing problems of
overheating and air pollution. A Climate Atlas was devel-
oped for the Stuttgart region, presenting the distribution of
temperature and cold air flows according to the city’s
topography and land use. Based on this information, a
number of planning and zoning regulations are recom-
mended that aim to preserve open space and increase
the presence of vegetation in densely built-up areas
(Kazmierczak and Carter 2010). In Stuttgart the preserva-
tion of the natural environment in urban areas is principally
guided by the Federal Nature Conservation Act
(BNatSchG), which prohibits the modification or impair-
ment of protected green spaces, or changing land use in
these protected areas (i.e. ‘‘zones in settlement areas, parks,
cemeteries, significant gardens, single trees, lines of trees,
avenues or groves in settled or unbuilt areas; and
some plantings and protective wood outside forests’’)
(Kazmierczak and Carter 2010). London and Stuttgart have
thus put in place policies that focus on arrow 2 and 3 of the
framework presented in Fig. 1, meaning that they call for
ecosystem conservation and an improvement of urban
Other examples of the implementation of projects and
policies to protect cities from hydro-meteorological hazards
through the restoration and management of ecosystem ser-
vices come from the US and Lao PDR. The ‘‘Grow Boston
Greener (GBG)’’ is a collaborative effort of the city of
Boston (USA) and its partners to increase the urban tree
canopy cover in the city by planting 100,000 trees by 2020.
The planting of these trees will increase Boston’s tree
canopy cover from 29 to 35% by 2030 as the planted trees
mature. The goals are to: ‘‘increase the tree canopy cover in
low canopy areas; mitigate the urban heat island effect
and reduce energy consumption through the appropriate
Sustain Sci (2012) 7:95–107 103
placement of trees on residential and commercial proper-
ties; improve air quality; and improve storm water man-
agement through strategic neighbourhood plantings’’
300a-4a28-9ac9-48681de04b07). This case is interesting as
it considers the multiple benefits and services that can be
derived by the same ecosystem, in this case the urban forest.
‘Integrating Wetland Ecosystem Values into Urban
Planning: The Case of That Luang Marsh’’ is an economic
assessment of the goods and services provided by the
marshes in an attempt to examine the economic value of
urban wetland biodiversity and its importance to people
living around the wetland as well as the larger urban area of
Vientiane (Gerrard 2004). Wetlands and marsh areas in and
around the city are important physical features and provide
hydrological functions such as flood control. There are
currently 175 flood-prone areas within the city limits, 70 of
which are located in the city’s core area. Flooding occurs at
least six times a year but in many cases flood-prone areas
will flood every time it rains. In the urban area of Vientiane
flooding is not deep, but frequent flooding causes damage
to buildings and roads, and interrupts transportation. The
value of the regulating ecosystem service has been mea-
sured as the annual value of flood damages avoided in these
areas and it will amount at close to US$ 3 million by the
year 2020 (Gerrard 2004).
Basing our analysis on the conceptual framework of Fig. 1,
we reviewed how locally and regionally generated and
well-managed ecosystem services can contribute to lower
the vulnerability of urban communities to hydro-meteoro-
logical hazards such as heat waves and floods. We also
reviewed studies that quantify, when possible, the role of
these ecosystem services.
Urban areas will continue to attract people who want to
settle in them because of the many economic advantages
they provide. It is therefore critical for urban areas to pro-
vide safe livelihoods to their populations, and although
urbanisation will always imply a change in ecosystems and
the services they provide, urban planning should system-
atically consider the role of ecosystems in buffering and
mitigating the effects of environmental hazards such as heat
waves and floods. In this respect, urban areas would benefit
from the restoration and adequate management of ecosys-
tems. Urban planners and managers should take into con-
sideration the role of ecosystems in reducing risks and
vulnerabilities (arrow 2 of Fig. 1). When establishing urban
development plans the presentation of landscape plans and
green open space structure plans should be taken into
account (arrow 2 and 3 of Fig. 1). Although urban areas will
generally create similar types of effects when it comes to
heat waves and flooding, the specific local climatic condi-
tions (e.g. urban heat island effect) will dictate the magni-
tude and frequency of the hazards and the urban ecosystems
the potential to buffer these. There are therefore no generic
sets of solutions to address the problems globally, but
adapted solutions need to be sought regionally or locally.
On the other hand, while designing strategies that make use
of ecosystem services to buffer cities, it is important to take
into consideration the effects of hazards on the ecosystem
itself (arrow 1 of Fig. 1). For instance, the right type of trees
(i.e. in general native species) or the right succession that is
more resistant to the impacts of hydro-meteorological
hazards should be identified to be planted. Overall we have
sufficient ecological knowledge on how cities can be buf-
fered by ecosystem services with respect to the reviewed
hydro-meteorological hazards. But we know little on how to
measure ecosystem services for hazard regulation, which is
an obstacle towards the design and implementation of
appropriate policies and plans. We propose here a series of
general recommendations to fill this gap:
ecosystem conservation and restoration play an
important role in lowering the vulnerability of urban
areas to hydro-meteorological hazards. A meta-analysis
of 89 restoration assessments in a wide range of eco-
system types across the globe indicates that ecological
restoration increased provision of biodiversity and
ecosystem services by 44 and 25%, respectively
(Benayas et al. 2009);
the vulnerability of urban communities and ecosystems
to hydro-meteorological hazards is influenced and
aggravated by the impacts of these hazards on ecosys-
tems and urbanisation. It is therefore necessary to
integrate disaster risk reduction, appropriate urban
planning and ecological restoration. For instance, in
areas where land-use pressure is considerable, ecosys-
tem services can be secured by leaving green and blue
areas in close proximity to one another, so that these
areas form larger nature and landscape entities (Nie-
¨et al. 2010);
one ecosystem my provide services for the regulation of
more than one type of hydro-meteorological hazard, as
is the case for green areas in cities. It is therefore
recommended to adopt a multiple-hazard approach;
generally cities are located in a watershed. The
management of ecosystems for the protection of cities
from hydro-meteorological hazards at this scale, which
transcends administrative boundaries, can provide
important elements of comparison of the vulnerability
of different cities.
Urban ecosystems provide essential services to cities
and city dwellers that are exposed to heat waves and floods.
104 Sustain Sci (2012) 7:95–107
Given the rapid urbanisation throughout the world and the
likely impacts of climate change in terms of these two
hazards, it is urgent to manage these ecosystems in a better
way than has been done in the past through integration of
ecosystem management in urban planning and disaster risk
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... Furthermore, the population decline of large grazing mammals may result in increased fires in savannahs, causing the release of CO 2 from ecosystems into the atmosphere (Johnson et al. 2018). It is also worth noting that preserved ecosystems act as natural buffers against extreme weather events, such as cyclones, floods and heat waves (Depietri et al. 2012). In this way, changes in land use must be integrated into climate models so that we can achieve a more detailed representation that increases our ability to predict how local impacts of change in land use will affect the future of biodiversity at a global level (Titeux et al. 2017). ...
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Since the establishment of the Intergovernmental Panel on Climate Change (IPCC), decision makers have realised that periodic assessments were needed to closely monitor climate change. Studies on it became widespread and include the science of greenhouse gas emissions, the composition of these gases and the extent to which humans have been responsible for climate change. In this sense, the United Nations summit has made significant progress since the Rio Conference (Eco 92), with the creation of the Conference of the Parties (COPs). However, governments should not solely focus on curbing greenhouse gas emissions into the atmosphere. In a society with broad and deep environmental problems, governments, the private sector and non-governmental organisations' (NGOs) efforts should include biodiversity conservation in their agenda. Solving a single problem, the climate crisis is honourable and urgently needed, but to constrain our ever-increasing land-use footprints on the planet needs the tackling of another equally challenging problem, the loss of biodiversity. The destruction of ecosystems undermines nature's ability to regulate greenhouse gas emissions and protect against extreme weather, thus accelerating climate change and increasing our vulnerability to it. Therefore, tackling environmental challenges means more than building electric cars, investing in "clean" energy and imposing fines on those who burn forests. To save the environment, scientists, industry , policy-makers and the wider society urgently need to look at other aspects of ecosystem conservation and restoration in the same way they look at the climate agenda.
... Globally, a number of studies have focused on flood mitigation and greenness association [94,95]. A study undertaken in Ghent, Belgium, focused on greenness to mitigate urban surface water flooding risk by developing a green infrastructure-based multi-criteria evaluation method [96] and found little research for planners and designers to determine an appropriate strategy for greenness planning. ...
... During the drought period, a gradual decrease in the amount of water vapor or carbon dioxide passing through the small pores of the plant is observed (Pavlidou et al. 2019). Because droughts occur at low latitudes, there is a strong negative relationship between the normalized difference vegetation index and land surface temperature (Depietri et al. 2012). Some studies are also performed for investigating the effects of earthquake on increasing the intensities of SUHI (Pavlidou et al. 2019). ...
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In this research, the effects of Covid-19 locked down and limitations on human activities were investigated on and urban heat islands. The multi-temporal images those were taken by the Landsat-8 OLI sensor in the spring 2017–2021 are used. For investigating the effects of lockdown in the spring of 2020, the status of surface urban heat island (SUHI) maps during the same period of lockdown in the three years before and the following year have been examined. The proposed method in this paper consists of two main steps; 1) producing the SUHI maps using the rule based analysis of land surface temperature (LST), normalized difference vegetation index (NDVI) and land use / land cover (LULC) maps.2) Quantitatively analyzing the behavioral changes in the SUHIs during Covid-19 locked down and compares their changes with the previous and subsequent years. The obtained results of performing the proposed post-classification change detection confirms that applying the locked down led to changes in the area percentage of high, medium and low SUHI classes by -17.61%, + 4.8% and + 12.8% respectively. Reducing the restrictions in 2021 caused to increase again the area of high SUHI class and decrease the areas of medium and low classes. In addition, the analysis of LST and NDVI obtained from Landsat-8 satellite images in the years 2017 to 2021 reveals that the Covid-19 locked down applied in spring 2020 caused a decrease of -22.52 in LST values and an increase of + 0.103 in NDVI compared to the average of its last three years.
In this paper, a time-conserving fragility curve formulation methodology for extreme events is discussed. Uncertainty is a parameter that has a significant effect on the probabilistic estimations of infrastructure failures. Structural damages to civil infrastructure range from minor defects to collapse relative to serviceability or restoration measures. In this paper, earthquake-induced landslides are used as a sample case study, to study empirical methods of fragility curve formulation. Method of maximum likelihood and best-fit regression methods are applied to an extreme event, and fragility curves are derived. Monte Carlo stimulation is applied to analyse the behaviour of uncertainty parameter concerning standard sections of highway and railway embankments. Finally, the coefficient of determination was calculated to illustrate the correlation between developed curves and data points. The proposed method suggests an optimum method to quantify the failure probability from an available data sample or a real incident-based data sample, which is computationally very effective. Improvement in vulnerability estimations provides high maintenance and efficient restoration schemes for transportation networks which are prone to extreme events such as landslides.KeywordsFragility curvesEarthquake-induced landslidesMaximum likelihoodMonte Carlo
Alongside rapid urbanization, the warm, humid tropical climate of Colombo exerts pressure on the city intensifying thermal discomfort. This could further create a negative influence on performing outdoor activities restricting the quality of life of urban dwellers. Therefore, creating a thermally comfortable urban space is significant. Yet, identifying the suitable tree species to provide better thermal comfort in Colombo has seldom been discussed. This study evaluates the impact on outdoor thermal comfort based on the physiologically equivalent temperature (PET) of five common species in Colombo; Cassia fistula, Tectona grandis, Plumeria obtuse, Mangifera indica, and Terminalia catappa. The field data collection was conducted on the sites of five selected species under both sunny and cloudy conditions. The parameters that contribute to assessing the urban thermal environment; sky view factor, relative humidity, air temperature, surface temperature, wind speed, solar radiation, and cloud cover were measured. The RayMan model was used to estimate thermal comfort by calculating PET values. The results indicated that the shading of trees can considerably influence outdoor thermal comfort expressed by PET. The lower PET values under the tree canopies indicated a lower level of thermal discomfort compared to an adjacent site, which was not directly shaded. Moreover, the one-way ANOVA test (p = 0.027) indicated that thermal comfort under Terminalia catappa was statistically different compared to Plumeria obtuse on sunny days. Additionally, among the selected species, Terminalia catappa was identified to be the most suitable species for improving thermal comfort in outdoor urban settings. The findings assist in the identification of species that offer greater thermal comfort in Colombo. As the use of appropriate tree species for shading is critical in alleviating heat stress, the results achieved can be employed as a measure of enhancing outdoor thermal comfort and as a vital initiative to achieve sustainability in Colombo.KeywordsUrban MicroclimateOutdoor thermal comfortUrban greeningSky View Factor (SVF)Physiologically equivalent temperature (PET)Colombo
Residential apartment buildings are widely implemented in Sri Lanka due to rapid urbanization and land scarcity. The confined spaces and controlled ventilation in such apartments could result in adverse health effects, including Sick Building Syndrome (SBS). Because of the usage of chemical products such as incense sticks in such compact spaces for religious activities in South Asia, SBS can occur. This study is one of the first field studies to establish a connotation between the indoor air quality of apartment buildings in Colombo, Sri Lanka, with various chemicals, including incense products and SBS. Measurements were taken from multiple locations in 50 apartments of various indoor environment parameters. Significant Total Volatile Organic Compound (TVOC) concentrations (up to 4.500 ppm) were associated with the use of chemicals, particularly cube-type incense products. Higher CO2 concentrations were associated with migraine and headaches. The relationship between chemical and incense products with higher levels of TVOC and SBS symptoms calls for urgent attention of the key urban planning stakeholders in Sri Lanka to improve ventilation and avoid using such products indoors.KeywordsSick Building SyndromeIndoor air pollutionIncense productsUrban high risersTVOC concentration
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The population living in urban areas is increasing day by day all over the world. Due to the increase in population in cities, social, economic, and environmental problems are also increasing. At the forefront of these problems is the formation of an urban heat island, which is one of the microclimatic negativities. Especially due to dense construction, changes in urban morphology, decrease in green areas and increase in impermeable surfaces increasing the formation of urban heat islands. Urbanization and global climate change, which are caused by human influence, have an impact on the environment, society, and economy. Unplanned construction, which emerged as a result of urban growth and population growth, reduces the resilience of cities in this process. However, it is possible to contribute to the creation of resilient cities with the strategies and planning decisions made in urban transformation applications made to prevent unplanned construction. The urban heat island, which is the biggest impact of climate change on cities, is a long-term process that threatens living things. In this process, which affects many areas, especially urban life, ecosystem, and human life, it is an important necessity to produce effective planning strategies for harmony and resilience. Evaluation of urban form optimizations is also important in this process. In this context, the study presents a systematic review of studies that deal with planning strategies within the scope of green infrastructure, architectural design, and albedo parameters, focusing on urban heat island effects, urban form, and landscape relationship in urban heat island formation.
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Urban green spaces are important for bird conservation, functioning as a buffer against the impacts of human actions on their surroundings. However, green spaces also provide several benefits to humans, such as the improvement of climatic conditions and a more intimate contact with nature. In this point of view, divided into three sections, we describe how ornithological research in a peri-urban vegetation patch in a tropical metropolis culminated in an environmental protection movement. This vegetation patch is composed of a mosaic of typical phytophysiognomies of the transition zone between two biodiversity hotspots: Cerrado and Atlantic Forest. Its vegetation presents characteristics that indicate high degradation, but the region still harbors 108 bird species (including threatened and endemic species), suggesting that even under intense impacts, the area presents characteristics of resilience to shelter the local biodiversity. Given these findings, we discuss the potential of this urban green space for scientific research, environmental education, and birdwatching. We highlight the possibility of influencing community engagement in the conservation of the area, whether for the preservation of charismatic species or for leisure and educational activities. Reducing the gap between academia and society can assist in the conservation of urban green spaces, especially in a region that presents high social environmental vulnerability.
Climate change is a global phenomenon that significantly disturbs urban life through occurrences such as urban flooding, resulting from extensive rainfall in the cities that are built up and consist mainly of concrete surfaces. The effects of climate change have been exacerbated by the urbanisation process in Africa’s major cities and towns. It has dominated contemporary debates in urban planning and development practice. As towns and cities continue to grow and climatic conditions endure change, the urban landscape continues experiencing negative effects of climate stress. The effects of climate change are felt by the natural and built environment, but they are mostly felt by people who inhabit these environments and reap benefits from it. Effects of climate change impact and are costly on service delivery, provision of infrastructure, housing, health and livelihood of the urban citizens. On the other hand, major African cities contribute significantly to climate change due to urban emissions. Built-up areas that include buildings, surfaced roads and concrete driveways prevent precipitation and storm-water to percolate into the ground. Climate change has direct and indirect effects on urban temperatures, rainfall intensity, built infrastructure, energy or power, hydrology and flooding, habitats and biodiversity. Open spaces, parks and places, gardens and streets provide critical services to the urban ecosystem, biodiversity and quality of life for urban citizens. The deliberate and conscious investment in policy and programmes that deal with climate change has been lagging in urban areas in Africa. The idea of developing urban infrastructure that adapts to climate change has not been fully exploited in African cities and towns. In most populated parts of major cities in Africa, the infrastructure is dilapidated and cannot adapt to climate change. Rapid urbanisation in Africa has reduced the capacities of major cities and towns to provide the required infrastructure and services that adapt to climate change. There has been a mismatch between existing urban infrastructure and population levels in major cities in Africa.
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An increasing amount of information is being collected on the ecological and socio-economic value of goods and services provided by natural and semi-natural ecosystems. However, much of this information appears scattered throughout a disciplinary academic literature, unpublished government agency reports, and across the World Wide Web. In addition, data on ecosystem goods and services often appears at incompatible scales of analysis and is classified differently by different authors. In order to make comparative ecological economic analysis possible, a standardized framework for the comprehensive assessment of ecosystem functions, goods and services is needed. In response to this challenge, this paper presents a conceptual framework and typology for describing, classifying and valuing ecosystem functions, goods and services in a clear and consistent manner. In the following analysis, a classification is given for the fullest possible range of 23 ecosystem functions that provide a much larger number of goods and services. In the second part of the paper, a checklist and matrix is provided, linking these ecosystem functions to the main ecological, socio–cultural and economic valuation methods.
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Ecosystem services are the benefits humankind derives from the workings of the natural world. These include most obviously the supply of food, fuels and materials, but also more basic processes such as the formation of soils and the control and purification of water, and intangible ones such as amenity, recreation and aesthetics. Taken together, they are crucial to survival and the social and economic development of human societies. Though many are hidden, their workings are now a matter of clear scientific record. However, the integrity of the systems that deliver these benefits cannot be taken for granted, and the process of monitoring them and of ensuring that human activity does not place them at risk is an essential part of environmental governance, not solely at a global scale but also regionally and nationally. In this chapter, we assess the importance of ecosystem services in a European context, highlighting those that have particular importance for Europe, and we set out what is known about the contribution biodiversity makes to each of them. We then consider pressures on European ecosystem services and the measures that might be taken to manage them. One of the key insights from this work is that all ecosystems deliver a broad range of services, and that managing an ecosystem primarily to © Royal Society of Chemistry 2010. deliver one service will reduce its ability to provide others. A prominent current example of this is the use of land to produce biofuels. There is an urgent need to develop tools for the effective valuation of ecosystem services, to achieve sustainable management of the landscape to deliver multiple services.
The effects of weathering on the aesthetic perception of oak wood (Quercus petraea (Matt.) Liebl.) were assessed through interviews realised on the same specimens before and after 500 hours of artificial UV weathering. About fifty people participated to each inquiry, regarding 17 pairs of pieces. Each pair was characterised before and after weathering by the difference of mean colour, colour variations and several ring pattern descriptors between both pieces. Two logistic regression models were proposed to explain the users’ choices through those measurements performed on weathered or non-weathered pairs of samples. The first inquiry, regarding non-weathered samples, showed that the users choose among two samples the one with the lightest, the more red, saturated and homogeneous colour and with the largest ring width. Regarding weathered samples, the users’ perception is slightly different: they still choose considering lightness, hue and colour homogeneity differences but no more considering saturation or ring width.
Estimates of air pollution removal by the urban forest have mostly been based on mean values of forest structure variables for an entire city. However, the urban forest is not uniformly distributed across a city because of biophysical and social factors. Consequently, air pollution removal function by urban vegetation should vary because of this spatial heterogeneity. This paper presents a different approach to evaluate how the spatial heterogeneity of the urban forest influences air pollution removal at the socioeconomic subregion scale. estimated using measured urban forest structure data from three socioeconomic subregions in Santiago, Chile. Dry deposition was estimated using hourly climate, mixing height, and pollutant concentration data. Pollution removal rates among the three socioeconomic subregions were different because of heterogeneous urban forest structure and pollution concentrations. Air pollution removal per square meter of tree cover was greatest in the low socioeconomic subregion. Pollution removal during 1997–1998 was different from 2000 to 2001 due to pollution concentration differences. Seasonal air quality improvement also differed among the subregions. Results can be used to design management alternatives at finer administrative scales such as districts and neighborhoods that maximize the pollution removal rates by the urban forest in a subregion. Policies that affect the functionality of urban forest structure must consider spatial heterogeneity and scale when making region-wide recommendations. Similarly, when model-ing the functionality of the urban forest, models must capture this spatial heterogeneity for inter-city comparisons.
Though the main reason for extreme floods in river basins are still extraordinary hydrometeorological events, the role of human influences on flood generation is growing world-wide during the last decades. Due to the economic consequences, the assessment of flood risks is most important in large river basins. On the other hand, it is primarily at the regional and local scale that political and technical measures can be taken rather quickly in order to reduce negative developments for the environment and society. The present study demonstrates how the impacts of extreme meteorological events in a river basin are and may be influenced by human actions. The influences of environmental changes on flood generation were studied in a meso-scale river basin situated in the German Elbe lowland. Extreme land use change scenarios as well as climate change scenarios assuming a 1.5K and 3K mean temperature increase during the next 50 years were used to assess the impacts of these changes on flooding risks in the basin.
When disaster strikes in cities the effects can be catastrophic compared to other environments. But what factors actually determine the vulnerability or resilience of cities? The Vulnerability of Cities fills a vital gap in disaster studies by examining the too-often overlooked impact of disasters on cities, the conditions leading to high losses from urban disasters and why some households and communities withstand disaster more effectively than others. Mark Pelling takes a fresh look at the literature on disasters and urbanization in light of recent catastrophes. He presents three detailed studies of cities in the global South, drawn from countries with contrasting political and developmental contexts: Bridgetown, Barbados - a liberal democracy; Georgetown, Guyana - a post socialist-state; and Santo Domingo, Dominican Republic - an authoritarian state in democratic transition. This book demonstrates that strengthening local capacity - through appropriate housing, disaster-preparedness, infrastructure and livelihoods - is crucial to improving civic resilience to disasters. Equally important are strong partnerships between local community-based organizations, external non-governmental and governmental organizations, public and private sectors and between city and national government. The author highlights and discusses these best practices for handling urban disasters. With rapid urbanization across the globe, this book is a must-read for professionals, policy-makers, students and researchers in disaster management, urban development and planning, transport planning, architecture, social studies and earth sciences.