Urban Heat Island in the Ljubljana City

Abstract

Ljubljana made the first climate mapping of the city in 2000, putting the differences in terms of UHI effects between the inner part of the city and the surrounding areas are quite evident. An efficient planning of city infrastructure takes into account increasing average temperatures in a city, and therefore provides solution to reduce and monitor the effect of its urban heat island. The chapter presents the urban heat island in the Ljubljana region, temperature modelling based on satellite data and UHI project pilot actions in the Ljubljana city.

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© The Author(s) 2016
F. Musco (ed.), Counteracting Urban Heat Island Effects in a Global Climate
Change Scenario, DOI 10.1007/978-3-319-10425-6_12
Chapter 12
Urban Heat Island in the Ljubljana City
B l a ž Komac , Rok Ciglič , Alenka Loose , Miha Pavšek , Svetlana Čermelj ,
K r i štof Ošt i r , Žiga Kokalj , and Maja Topole
Abstract Ljubljana made the fi rst climate mapping of the city in 2000, putting the
differences in terms of UHI effects between the inner part of the city and the sur-
rounding areas are quite evident. An effi cient planning of city infrastructure takes
into account increasing average temperatures in a city, and therefore provides solu-
tion to reduce and monitor the effect of its urban heat island. The chapter presents
the urban heat island in the Ljubljana region, temperature modelling based on satel-
lite data and UHI project pilot actions in the Ljubljana city.
Keywords Urban heat island • Urban heat island atlas • Satellite termography mea-
surements • Pilot actions • Ljubljana • Slovenia
12.1 Introduction
Urban heat island is an urban area where temperatures are higher than in the sur-
rounding area. This is mainly due to the accumulation of heat in buildings, concrete
and asphalt land during the day. This leads to a greater night long wave radiation
from the surface and thus to a smaller cooling than the surroundings (Žiberna 2006).
The city also has lower albedo, greater diffuse solar radiation due to pollution,
reduced evapotranspiration and lower relative humidity which infl uences quality of
life (Ravbar et al. 2005 ; Tiran 2016 ).
B. Komac (*) • R. Ciglič • M. Pavšek • M. Topole
Anton Melik Geographical Institute ZRC SAZU , Novi trg 2, 1000 , Ljubljana , Slovenia
e-mail: blaz.komac@zrc-sazu.si
A. Loose
Energy Manager of the City of Ljubljana , City of Ljubljana ,
Adamič-Lundrovo nabrežje 2, 1000 , Ljubljana , Slovenia
S . Č ermelj
Department of Environmental Protection , City of Ljubljana ,
Zarnikova 3, 1000 , Ljubljana , Slovenia
K. Oštir • Ž. Kokalj
Institute of Anthropological and Spatial Studies ZRC SAZU ,
Novi trg 2, 1000 , Ljubljana , Slovenia

324
In Ljubljana, urban heat island was fi rst detected when creating The climate map
in 2000 (Fig. 12.1 ). Area with above-average temperatures was lying between the
Rožnik and Golovec hills (Rejec Brancelj et al. 2005 ; Smrekar et al. 2016 ). In the
context of climate map guidelines for spatial planning were prepared, which pre-
served the green wedges and fresh air corridors for the city centre (Internet 3 ).
During the UHI project we found that the development of the city and in particu-
lar the construction of many shopping centres with large parking places increased
the intensity of urban heat island phenomenon. The project was designed primarily
for mitigating as well as adapting to this phenomenon and thus climate change.
12.2 Meteorological Measurements
During the project the urban heat island index was calculated for the Ljubljana
Bežigrad (46 °07′ N, 14°52′ E, 299 m a.s.l.) and Brnik (46 °22′ N, 14°22′ E, 364 m
a.s.l.) meteorological stations (Internet
1 ). The Ljubljana Bežigrad weather station
is within the inner circle of the city. The area is representative for a typical urban
Ljubljana setting, 1.5 km away from the city centre. The weather station is a synop-
tic one and thus equipped with many for the UHI-recognition meteorological
Fig. 12.1 Climate chart of Ljubljana showing the urban heat island area
B. Komac et al.

325
devices (Internet 1). The Brnik weather station is in a complete rural area and stands
on the SE edge of the Jože Pučnik Airport runway, over 100 m NW from it and more
than 1 km away from the nearest bigger building. First larger forest area is over the
airport’s runway more than 500 m away. The surrounding terrain is in general fl at,
open and grassy. Weather station is a climate one and the measurements are taken
automatically. The air distance between both weather stations is something more
than 17 km; the difference in altitude is 65 m (Fig. 12.2 ).
The UHI intensity-cycle was calculated for the period July 20. to July 26. 2011.
Its intensity was quite similar every day. The lowest intensity was present in the
morning of the second day, when the heating at the rural station has started earlier
than at the urban station and it was signifi cantly more rapid. Before a midday the
urban station became warmer, but in the evening rural station was cooling
signifi cantly faster. That caused that UHI intensity has reached the third highest
Fig. 12.2 Mean hourly air temperature and wind speed data in urban and rural station
12 Urban Heat Island in the Ljubljana City

326
value in the selected period (4.95 K). A little higher air humidity compared to fol-
lowing days in the period was probably a cause for thin-fog formation near the
middle of the night, which has decreased cooling rate at the urban site. In the whole
period wind was varying from calm in the night/early morning time to the top speed
around 2–3 m/s in the afternoon on the both stations. In the beginning of selected
period the prevailing wind was weak mid-atmosphere NE winds, which usually
doesn’t reach the valley’s bottom. That is why none of the stations shows a signal of
constant NE winds. The measured wind variations were thus thermally driven by a
daily heating and nocturnal cooling, because in the selected period the sky was clear
all the time. The biggest anomaly of the wind in the selected period occurred during
the day on the 24
th of August, when the wind direction in the middle altitudes has
changed to SW, which descends over the Dinaric Mountains to Ljubljana basin and
has some characteristics of the foehn wind. Also the air humidity was the lowest in
that time at the both stations. A weak SW wind was blowing till the end of a selected
period and very low humidity has caused the lowest night-time temperatures
especially at the rural station and thus the UHI intensity has raised for 0.5–2 K
(Figs. 12.3 and 12.4 ).
Fig. 12.3 Mean urban heat island intensity data
B. Komac et al.

327
12.3 Satellite Thermography Measurements
Effi cient planning of city infrastructure and its activities has to take into account
increasing average temperatures in a city, and therefore consider and monitor the
effect of its urban heat island (Zakšek and Oštir 2012 ).
Land surface temperature can be monitored with satellite systems (Colombi
et al. 2007 ). To assess the extent and state of urban heat island of Ljubljana we used
Landsat 8 imagery that has adequate spatial resolution for a detailed analysis of
temperature variations (Bechtel et al. 2012 ). Images of Ljubljana and its vicinity are
acquired twice every 16 days. Land surface temperatures were calculated from two
cloudless images per season in the period between April 15
th 2013 and March 8
th
2014.
Fig. 12.4 Mean heat degree days (HDD) and cold degree days (CDD) in the period 1980–2011 for
Ljubljana
12 Urban Heat Island in the Ljubljana City

328
The area of interest was divided into three zones, with the fi rst being inside the
city ring road, the second a 3 km band from the fi rst, and the third a 2.5 km band
from the second. The zones have been further divided according to land use; we
have grouped the classes into: built up, water, agricultural land, and forest. Build up
and water areas smaller than the resolution of the thermal band (1 ha) were excluded
from the analysis. The fi rst zone was further partitioned to city districts, and the
second and third zones to areas of settlements.
Comparison of temperatures included build up areas of smaller cities close to
Ljubljana (Kranj, Domžale, Kamnik, Grosuplje, and Vrhnika) and some of the
city’s more interesting regions (the centre, industrial areas, business-shopping cen-
tres, areas of individual housing, and parks). The impact of water and trees on the
surrounding surface temperature was assessed with profi ling – across the whole city
and through specifi c areas of interest.
We have found that Ljubljana exhibits a distinct urban heat island. Furthermore,
some of its districts are constantly warmer than others, and specifi c areas are defi ni-
tive hot spots (Figs. 12.5 and 12.6 ).
Fig. 12.5 The frequency of occurrence of the top two percent of the highest temperatures in build-
up areas
B. Komac et al.

329
12.4 Urban Heat Island Atlas
The Urban heat island atlas is an internet application for visualization of spatial
data, related to urban heat island in the area of Central European countries (Ciglič
and Komac 2015 ). The database was elaborated in GIS environment using ArcGIS
Desktop and published online using ArcGIS Server. This project result is intended
to support decision-makers in the fi eld of spatial planning and is therefore free-
accessible to everyone at http://zalozba.zrc-sazu.si/p/1352 .
The atlas presents urban heat island infl uencing factors including elevation, nor-
malized difference vegetation index, land use (Corine land cover and Urban atlas
data), human activity shown by night scene image (detected by VIIRS sensor data),
air temperature at 2 m and land surface temperatures (Komac and Ciglič 2014 ).
Viewer can analyse the data by making profi les across the temperature layers for
April and August (at 2 p.m.). In this way, temperatures in the city and the surround-
ings can be compared (see the example of Ljubljana in Fig. 12.7 ).
Various local and regional datasets provided by the project partners are also pre-
sented in the atlas.
The atlas was prepared by the Anton Melik geographical institute ZRC SAZU
and Hungarian meteorological service.
12.5 Mitigation of the Urban Heat Island in the Ljubljana
City Area
The purpose of the project was to establish the existence of a heat island, which was
confi rmed by data from meteorological stations and satellite thermography, and
then use this knowledge to mitigate the effects of heat islands.
Fig. 12.6 Profi les of summer land surface temperatures across Ljubljana, with indicated land use
and prominent orientation points. The location of the profi le is marked as a red line on Fig. 12.5 but
it extends beyond the boundaries of the fi gure
12 Urban Heat Island in the Ljubljana City

330
As urban island is affected by several factors such as green areas in the city,
location and design of the land use, types of building and roofi ng materials, layout
of buildings, and their energy effi ciency, including spatial development of the city,
we examined some of the characteristics of the city of Ljubljana. We carried out
some pilot actions to draw attention to the importance of taking into account the
effects of the urban heat island in the planning of land use and activities in the city.
In 2010 the Municipal spatial plan (Internet 2 ) was adopted defi ning the planned
land use with special focus on urban land uses and future development of green
areas (Fig. 12.8 ).
In order to minimize the effects of the urban heat island the basic strategic objec-
tive of the Ljubljana city is to create an interconnected and transparent network of
open public spaces of high quality. During several last decades an action called
»Ljubljana – My Town« has been under way. It stimulates the facades’ renovation
all over the important public areas or representative areas.
One of the most important measures is preserving the city green areas and pro-
tecting the city forests as a part of green wedges. A specifi c feature of the city is its
green ring, a way along barbed wire, which encircled the city during the WW2
being a popular recreational area. The focus area is the axis along the river of
Ljubljanica and green areas along the Sava river, the Gruber’s canal, the Špica bank,
and the Gradaščica and Glinščica brooks.
Fig. 12.7 Print screen of the Urban heat island atlas. Its user friendly interface enables users to
select between different layers, make profi les across April ( as below ) and August temperatures in
Central Europe and zoom to UHI partner data
B. Komac et al.

331
Related to green areas a special attention is given to open public areas network
that connect the surrounding of the city with its squares, streets, riverbanks and
walkways, and also serve as an air-corridor network. They create micro-climatic
and mesoclimatic conditions, enable ventilation of the city. The stretches of water-
ways also constitute a system of open public spaces. Adequate directions for protec-
tion and management are defi ned for such areas.
The extent of pedestrian areas increased lately due to the traffi c limitation and
complete stop in inner city centre. Still, poor airing is presented in the Ajdovščina
area. The city planning measures regain pedestrian areas that would make various
social interactions possible. Urban ventilation is therefore an important factor of
urban heat island mitigation, and connecting natural areas in landscape parks with
the city.
In Ljubljana garden-plot areas were spontaneously developed and distributed
across the entire fl at area of Ljubljana. Due to a urban lifestyle and a policy change
by the city authorities, the area of garden plots fell considerably at the end of the
twentieth and the beginning of the twenty-fi rst centuries. Until recently garden plots
were spread on 200 locations and covered 1.3 km
2 (Jamnik et al. 2009 ) Due to
pesticide residues and heavy metals in the soil and produce, as well as groundwater
contamination, plot gardening poses a threat to public health and the environment,
and the 2008 Ljubljana Zoning Implementation Plan reduced the total area of plot-
gardening areas by nearly half.
Another way of minimizing the effects of urban heat island is related to building
and roofi ng materials. The majority of old buildings in the centre of the Ljubljana
city are built of bricks and stone. In the broader city area concrete buildings were
built in the 1970’ and 1980’, while iron was used to build some new high buildings.
Fig. 12.8 Future development of green areas in the City of Ljubljana (Internet 3)
12 Urban Heat Island in the Ljubljana City

332
Most of the stone and brick buildings in the old city are plastered, while stone was
used primarily for portals, window frames and in some cases, pet mats. Mitigation
is diffi cult due to the fact that the Ljubljana centre was declared a cultural and his-
torical monument, which requires full protection of the cultural, aesthetic, historical
and natural values (Decree … 1986 ). Common roofi ng material in Ljubljana is tiles.
Tiles cover the majority of older buildings in the centre of the city. Some atriums of
the buildings have been covered by glass and only few buildings and winter gardens
have been equipped by green roofs until now, built mostly by incentives of individu-
als (Črnuče, Lek pharmaceutical company, Maros company) or by public funds
(Stožice sport park a green roof with size 8000 m
2 ).
12.6 Pilot Actions
The notion of spatial organisation as a method of urban management has been
adopted in three typical areas of the City of Ljubljana: the city centre, suburban area
and hilly hinterland. This division is merely schematic as it would be diffi cult to
demark these areas where the contents are intertwined (Decree ... 1986 ).
In Ljubljana 21 streets in the centre of the city have been closed to traffi c since
2006. The public cycling system Bicikelj has been established in 2011. In some
areas in the city centre the allowed speed of traffi c was reduced to 30 km/h, allowing
safer cycling and pedestrian transport.
The 2010 Municipal spatial plan defi nes land use activities from urban land use,
green areas, cycling routes and green areas points of view.
A number of drinking fountains were established in the city centre next to several
fountains. In 2010 two new parks measuring 15 ha have been established: the
Northern park and the park at the Šmartinska street. The city of Ljubljana is taking
care of more than 72,000 trees in the city and its surroundings. More than one hun-
dred trees were planted in the streets of the city centre in 2009 and more than 250
trees were planted in 2010 as a part of a project the Labyrnth of Art. About 1409 ha
of forests on the nearby hills (Rožnik, Šišenski hrib, Grajski grič, Šmarna gora and
Grmada) were given a status of forest of special importance, although almost 90 %
of the forests are a property of private subjects. Next to a new stadium and sport hall
about 90.000 m
2 of green areas (parks and sport areas including cycling and running
tracks) next to 5000 m
2 of play grounds are going to be built. Also, the Ljubljanica
river banks were reconstructed in order to allow public access to water in the city.
Large areas of the city dump in the Ljubljansko barje area were transformed to golf
links ( http://www.ljubljanapametnomesto.si/ ). A list of buildings which are acces-
sible for disabled people has been made public ( http://www.disabledgo.com/sl/org/
ljubljana ).
The determination of pilot Urban Heat Island installations locations was a sub-
ject of numerous consultations and debates within the City administration and pub-
lic. Some of them were realized in 2013, the others were prepared and installed this
year.
B. Komac et al.

333
12.6.1 Ambient Urban Intervention “Boats in the Fountain”
on the Plateau in Front of Slovenian Ethnographic
Museum (SEM), June, 2013
The architectural concept of the plateau in front of the SEM in the very city centre
is a part of a collage of various surfaces and objects. Some of the surfaces are less
used that expected, as is the case of the 260 m2 plateau, that was planned as a water
surface, but was not realized for years. In the summer period, water is one of the
most important elements of public space – it cools the ambient and represents an
ideal playground for children. Water also reminds us on holidays, sea, boats, …, and
is especially attractive for children. For those reasons we have decided to restore the
project and to realize the long-time ago planned water surface in an innovative way
that will be attractive for public.
In June 2013, the ambient intervention “Boats in the fountain” was realized, by:
– re-establishment of water surface,
– establishment of spaces where it is possible to play, work or rest,
– rearranging the area to bring it closer to the children and adults.
For the installation old boats were used, after the detailed renewal, each of them
had its own name and own story. It became an ideal meeting place for all genera-
tions. Throughout the whole summer period numerous visitors enjoyed the vicinity
of water surface, especially children. The project was concluded by the end of
September (Figs. 12.9 and 12.10 ).
12 Urban Heat Island in the Ljubljana City

Fig. 12.9 Project baseline – Slovenian ethnographic museum (SEM)
Fig. 12.10 SEM – realized water surface

335
12.6.2 Temporary Installation on the Central Section
of the Slovenska Street after its Closure to Traffi c
(September 2013)
Since September 22, 2014, the central part of Slovenska street, passing through the
very city centre was closed to motorized traffi c, with the exception of public trans-
port. With this measure the transit of motorized vehicles is being reduced in the city
centre and the priority of using it is given to pedestrians, cyclists and public trans-
port. On the occasion of closing the street a temporary arrangement was designed
and realized to show the citizens and tourists what they can gain from the street
closure. The project of temporary arrangement was planned in a sustainable way
according to the principle “Less is more” (or “More with less”). All elements may
be moved from one location to another, whenever needed. Besides street markings
no element will be used for the Slovenska street only. Temporary arrangement com-
prised of:
– information point (Info point) about new arrangement of the Slovenska street –
citizens were invited to give additional proposals for additional installations or
improvement of the existing,
– potted groups of trees (wooden pots),
– smaller permanent green plants in pots – pocket parks,
– Tables and chairs,
An info point-container in which the exhibition of the projects concerning the
new look of the street was prepared together with the exhibition showing the history
of the main street. Numerous citizens and other visitors gave their proposals for
improvements and compliments. It is important that the citizens were satisfi ed with
new arrangements, using the newly gained space daily. With additional plants (green
areas) an effort was taken to improve local environmental conditions and to estab-
lish more attractive street ambient. The black-carbon and nitrogen dioxide measure-
ments were performed on-site as well (Fig. 12.11 ).
12.6.3 Green Gym – Gymnastic House with Green
Roof (April 2014)
The prototype of small green gymnastic house with green roof was designed and
built. It was designed for adults, to be placed on public playground for children to
serve for parents and other adults while their children are playing. The time, usually
spent waiting for children on the bench, has changed into the active/healthy recre-
ation and can serve as an example of a good practice for children, as well. The gym-
house is placed on recently renewed playing ground in the city centre.
The gym-house was named “Always young” has a base of 6 m
2 and is about 3 m
high. It consists of the metal construction that serves as well as a gymnastic object,
12 Urban Heat Island in the Ljubljana City

336
solid roof planted with extensive growing grass on wooden base reinforced by metal
sub-construction. As the installation is placed outside, the rain will be enough for
the watering of the roof. In the house a simple construction consisting of three basic
gym equipment suiTab. for both genders and ages are available. The gym house is
funded on concrete foundation. Within the area of 1.8 m around house, material that
buffers falls is spread. On the walls there is a Table with instructions how to exercise.
As the gym-house is a part of the playground for children it was planned and built
in such a way that it meets the standards (the gym-house is certifi ed) (Fig.
12.12 ).
Fig. 12.11 Temporary installation on the main street (Slovenska ulica) soon after its closure
to personal motorized traffi c
B. Komac et al.

337
Fig. 12.12 Children and parents playground – the gym-installation for parents with the green roof
was added to the classical playground for children, with the invitation letter ( right )
12 Urban Heat Island in the Ljubljana City

338
B. Komac et al.

339
12.6.4 Pocket-Parks in the Streets with Parking
Places (April 2014)
Pocket parks are representing the long-term cultivation of public-spaces. With these
installations we are trying to develop a method for revitalization and remediation of
degraded spaces in the built part of the city centre. The interventions are not only
artistic installations but also a serious search of new urban possibiliries for better
use of urban spaces. The main objective is to pay special attention and to reveal
selected city areas.
Pocket-parks are a kind of containers with the dimensions of a single parking
place (car) that can play a certain role, with its planted part, to mitigate the UHI
phenomenon on the micro-scale within the densely built area in the city centre.
Since May 2014 it is possible to enjoy on one of the pocket-parks, called
PARKplac (PARKplace) on four streets and one square. They are equipped accord-
ing to the reuse concept. Local inhabitants and local merchants will take care about
them. With these installations we are addressing the citizens to the new approach to
the public space and spreading the 3R idea (Reduce, Reuse, Recycle). According to
the 3R approach all materials that are used were taken from past installa
12 Urban Heat Island in the Ljubljana City

340
tions.
12.6.5 Planting Trees (April 2014)
By planting trees we are trying to increase the quantity of green areas in the city.
Trees have been planted on three locations according to the standard SIST DIN
18916.
Near the Nove Fužine block-settlement the new park “Art Labyrinth” was
planted. The Art labyrinth is bringing together the park as a green public area with
the labyrinth art tradition, artistic approach and literature (book reading). The park
is a kind of growing and development feature as it grows with its visitors. The more
care that it is being given and the more trees that are planted, the bigger is the place
where we can rest in peace and read a good book.
B. Komac et al.

341
12.6.6 Promotion of the Project
On different occasions the UHI project was promoted (opening the pilot installa-
tions). One of them was also the project “For the cleaner city” that was taking place
through the whole city area from 22
th March to 22
th April, 2014.
12 Urban Heat Island in the Ljubljana City

342
The project was promoted by the lectures about UHI phenomenon, public polls
considering the pilot actions and general opinion on climate change, delivering the
UHI gadgets and leafl ets, see fi gures below.
B. Komac et al.

343
12.7 Conclusions
The urban heat island project gave us a comprehensive scientifi c insight in the phe-
nomenon, useful tools and instructions for adaptation and mitigation of urban heat
island effects. At the same time it was proved that our efforts in the past were suc-
cessful preserving the important green areas (wedges) and fresh air corridors.
We are satisfi ed with a big success of the project that can be recognized by the
number of people that were involved and mobilized by its activities.
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