Climate-proof cities: City of Tallinn, Estonia

Surface Permeability

Surface permeability is regarded as one of the key indicators of climate resilience.

Two time scales have been selected for assessing the surface permeability in the city of Tallinn: current situation (contemporary permeability) and future permeability. It was assumed that greenery areas have good surface permeability and that greenery ratios (percentage of greenery set for each land use type in district comprehensive plans) are equivalent to such permeability.

Contemporary permeability

Base map: Land cover layer of Tallinn City TAR

Methodology: Different surface types in Tallinn City TAR were divided into two groups:

1. Permeable surfaces:

1. Wood
2. Flintstone
3. Gravel
4. Sand
5. Cobblestone
6. Soil
7. Limestone
8. Artificial lawn

2. Impermeable surfaces:

1. Asphalt
2. Concrete
3. Rubber
4. Tar paper

The percentage of permeable surface of each map polygon was calculated. The percentages were classified into four classes: Class 0: 0-10% permeability (in red colour), Class 1: 11-40% (in orange), Class 2: 41-70% (in yellow) and Class 3: 71-100% (in green) and represented on the map.

Summary of the contemporary map (2653 polygons in total):

Class 0 – 103 polygons, 4% (in red)

Class 1 – 395 polygons, 15% (in orange)

Class 2 – 779 polygons, 29% (in yellow)

Class 3 – 1376 polygons, 52% (in green)

Currently, the lowest share of surface permeability (Class 0 and Class 1) covers about 20% of the polygons, while more than half of the polygons has the maximum share of permeability (Class 3) (Table 1 and 4).

Table 1. Current surface permeability in Tallinn districts

Future permeability

Base map: Land use maps of 7 district comprehensive plans. In the case of City Centre District (Kesklinn) the thematic plan of green areas in Tallinn was used.

Methodology: Planned greenery ratios per land use type for each map polygon were taken from the district comprehensive plans and assumed to represent future permeability in each polygon. Comprehensive plans of 8 city districts, where the greenery ratio is set as follows:

Table 2. Proposed greenery ratios per land use type in district comprehensive plans in Tallinn

Based on the greenery ratios set in district comprehensive plans, the future soil permeability

Table 3. Future soil permeability in Tallinn districts

If the greenery ratios proposed in the district comprehensive plans would be implemented to the full extent (Table 2), the surface permeability would decrease (Table 3). The most significant reduction would be in Class 3: from 52% to 20% and in Class 1, where the number of polygons with greenery ration between 11 and 40% will almost equally increase (Table 4).

Table 4. Surface permeability classes today and in the future in Tallinn

Map 2: Surface permeability in Tallinn today (left) and in the future (right), if the comprehensive plans would all be put into action. 

The comparison between the contemporary and future permeability map indicates that the number on polygons in the lowest permeability class (Class 0) will decrease (from 4% to 2%), which seems a positive development (Table 3 and 4; Fig.2., map on the right), alluding that the worst areas of surface permeability will improve. However, the number of polygons in Classes 2 and 3 will also decrease and most of the polygons (54%) will fall into Class 1, having the second lowest permeability ratio (between 11% and 40%) of the polygons (Table 4). Today, 52% of the polygons are in good permeability condition (Class 3: 71-100% of permeability).

While looking at the future surface permeability scenario across districts, 5 districts out of 8 would experience rather significant reduction in surface permeability if the proposed greenery ratios in comprehensive plans would be strictly followed (Table 5). The most pronounced changes may take place in Haabersti district, since the number of polygons in Class 0 and 1 (the least surface permeability) could increase by 10-fold compared to the contemporary situation (from 5,4% to 54,9%). Also Kristiine, Lasnamäe, Mustamäe and Põhja-Tallinn may experience significant surface permeability reduction resulting from greenery ratio reduction in polygons, but at different scales.  The least changes in the future compared to today’s situation would occur in Nõmme, Pirita and Kesklinn, where the greenery ratio has already been set high in comprehensive plan. For example, in Nõmme the suggested greenery ratio ranges from 40 to 50% and in Pirita even as high up to 75-85%. While the greenery ratio in Kesklinn (City Centre) has not been set particularly high, ranging from 15 to 40%, and in city forests up to 50%, the future scenario would not considerably differ from the today’s situation. One of the reasons may be the fact that the land use in City Centre has already taken shape and the objective is to maintain the green areas rather than to reduce them.      

However, in five districts the surface permeability in Tallinn could decrease significantly, if the district comprehensive plans become fully implemented.  

Table 5. Possible future surface permeability in districts and per permeability class

Canopy cover

Canopy cover percentage (also canopy overlay) is regarded as one of the indicators of urban climate resilience. Canopy cover plays an important role in reducing high temperature (heat wave) impacts on citizens and slows down the stormwater runoff by allowing more retention time to either infiltration of the water into the soil or flowing into stormwater collectors, and by that reducing the risk of flooding.

Canopy cover (overlay) in Tallinn

In this study, the tree canopy cover is expressed as the percentage of the ground area shaded by tree canopies relative to the total open area. No quality criteria were applied.

Only the contemporary situation was analysed in this study. The possible future canopy cover ratios in polygons depend on the implementation of the district comprehensive plans (if the greenery ratios proposed in these plans are strictly followed) and on the potential increase of construction pressure and associated tree cover loss. On the other hand, tree cover ratio may increase in some polygons that are currently brownfields with some greenery. If those underdeveloped areas are left aside for decades the tree canopy cover percentage may improve naturally. All these assumptions need additional analysis.

The following results were obtained.

Contemporary canopy cover

Base map: LiDAR-based vegetation elevation model of Tallinn.

Methodology: The vegetation elevation model contains 10x10 m cells with information of vegetation height in each cell. Cells where the vegetation height was between 5 and 30 m were extracted from the model. Cells with lower vegetation height were discarded because either they do not indicate trees or the trees are too small to offer proper ecosystem services. Cells with higher vegetation height were discarded because they contain more likely classification errors. 

Percentage of canopy cover of each map polygon was calculated. The percentages were classified into four classes: Class 0: 0-10%, Class 1: 11-40%, Class 2: 41-70% and Class 3: 71-100%. The colours of the classes are represented on the map (Map.3.).

Map 3: Current canopy cover in Tallinn, percentage classes

Table 5. Contemporary canopy cover in Tallinn districts, no of polygons per canopy cover class

As described in Table 5, there are big differences between the Tallinn districts in canopy cover classes. The largest contemporary canopy cover among the Tallinn districts is in Nõmme, where 87% of Class 2 and 3 polygons are located, whereas Lasnamäe holds 2,6% of Class 2 and 3 polygons only.

Since the canopy cover and surface permeability depend on the greenery ratio, it is crucial for the city planners to maintain the ratio of greenery at current level since it provides good prerequisites for climate resilience. Any reduction would lead to the reduced climate resilience and associated wellbeing of citizens. 

Access to public green areas

Access to public green areas has been regarded as essential for quality of life and wellbeing of local residents. Local authorities have an important role to ensure the public access to green areas via planning process.

Access to public green areas in 250m distance in Tallinn

In the current study, firstly, the availability of green areas of at least 0,75 ha (7500 m²) in size, secondly, the population in 100x100 m cells and thirdly, the number of residents living within 250 m radius of the green areas was mapped.

The following steps were taken.

Base map: Thematic plan of public green areas and a map of inhabitants in 100x100m cells. 

Green public areas are green areas for public use. It should also be noted that Tallinn City has green areas of private use (e.g. relatively large private gardens in the districts of Pirita, Nõmme, Kristiine). Thus, the access to green areas describes only the accessibility of citizens to public green areas, while the accessibility to green areas is much better if private green areas are also taken into account. But, in this study, only public green areas are considered.

Methodology: The map of inhabitants in Tallinn consists of 100x100 m quadrate cells with population data. As of 1 January 2018 there were 427 201 inhabitants in Tallinn.

The map of public green areas of Tallinn contains 197 polygons larger than 0.75 ha (Table 6; Fig.4.). 41% of the polygons are up to 2.5 ha large. The second size class (2.5-10 ha) covers 58 polygons (29%). There are also 23 polygons that cover more than 50 ha of public green areas. These are protected areas, such as Natura 2000 sites and water protection zones covered by forests.

Table 6. Number of polygons across size classes of public green areas in Tallinn 

Map 4: Current access to public green areas in Tallinn, dependant on green area size class 

There are 5490 by 100x100m cells across Tallinn city (Table 7). Population density in the city is rather low, since majority of the cells (65%) have less than 50 people. The population density is higher in districts with apartment houses, such as Mustamäe, Haabersti, Lasnamäe and North-Tallinn (Table 8; Map 5.).

Table 7. Citizens’ density in 100x100 m cells in Tallinn

Map.5 

Map 5: Number of Tallinn citizens in cells (5 classes).

Table 8. Number of 100x100 m cells and number of citizens per population size class

Table 9. Access to public green areas by citizens in districts, up to 250 m and further distance 

A 250 m buffer was constructed around the public green areas and population cells were differentiated based on whether their centroid was inside or outside of the buffer. According to the analysis, 79% of the population of Tallinn lives in a distance of 250 m or less to a public green area with at least 0.75 ha size (Table 9-11; Fig.6.).  The best access to public green areas appears to be in districts of Pirita, Kesklinn and Põhja-Tallinn, where 85 to 97% of the people in these districts have access to a public green area closer than 250 m. The district of Lasnamäe outstands the other districts, since the citizens have the least access to a public green area in their closest vicinity:  55% of the district population have access to a public green area further than 250 m of home (Table 10).   

Table 10. Access to public green areas by citizens 

Map 6: Access to public green areas closer and farther than 250 m in Tallinn.

Table 11. Citizens’ distance from public green areas in districts

In conclusion, the study results demonstrate that majority of the residents of Tallinn city (about 80%) has a rather good access to public green areas (of at least 7500 m² large) in their closest vicinity of 250 m. In addition to the access to public green areas also privately owned gardens in the districts of Kristiine, Nõmme and Pirita play an important role in providing recreational and climate resilience services to the citizens.