2016/ Bioclimatic Green Cell – Category C
**A CONCEPTUAL PATTERN FOR SUSTAINABLE AND LIVABLE URBAN ENSEMBLES**
URBAN CONDITIONS IN TEMPERATE CONTINENTAL CLIMATES
Urban microclimates in temperate continental areas (such as Eastern Europe) are characterized by a regime of moderate rainfalls with dry summers (especially in the last decades) and a significant difference in temperature between winter and summer. Thus, the main bioclimatic challenges comprise high summer temperatures, due to the high levels of sunlight and heat radiation, a low air humidity level and a reduced precipitation regime, especially in July and August. In the winter, the bioclimatic comfort is affected by low temperatures and cold winds sometimes associated with blizzards and heavy snowfalls which affects the exposed areas. In urban areas, the bioclimatic discomfort is usually exacerbated by the relatively high degree of air pollution with noxious gases and dust, especially because of the heavy car traffic. Also, the bioclimatic conditions in urban environments may be affected throughout the year by a low level of air ionization, oxygenation and carbon sequestration. Starting from the complex ability of the woody vegetation to modify the microclimatic conditions, a bioclimatic landscape zoning concept for urban ensembles located in temperate continental areas is proposed.
“BIOCLIMATIC GREEN CELL”
The bioclimatic landscape zoning concept is based on the identification and classification of four major types of green areas with distinct bioclimatic roles. The placement and sizing of the green areas depend on the microclimatic impacts and on the “action radius” of each bioclimatic zone. The covered issues within the bioclimatic planting design guidelines refer to: vegetation type selection, tree canopy density, leaf area index (LAI), habitus of plants, trees height, etc.
Thus, the four types of the bioclimatic areas include: A. Protection Zones (Shelterbelts); B. Mobility Zones (Green corridors and platforms); C. Buffer Zones (Green infrastructure which protects the built area); D. Complex Zones (The green-blue core has a complex bioclimatic role and serves also as a leisure area). The hexagonal shape of the diagram is purely conceptual and serves to highlight the eco-climatic context and the possibility to develop bioclimatic green cells networks using this module at different scales. Thus, in the case of further project implementations based on this concept, areas and shapes may vary subject to the proportions and conditions set forth below.
The “Bioclimatic Green Cell” concept is based on introducing shelterbelts (Zone A) around an urban or peri-urban ensemble to create a favourable microclimate by reducing the speed of the prevailing winds, purifying the polluted air, increasing air ionization, rising the atmospheric humidity level during summer and reducing the urban noise. The shelterbelts are substantially wider in the areas exposed to the prevailing winds. So, three types of shelterbelts are proposed: A1 - summer deciduous plantations (on the W-SW side); A2 - winter mixed plantations (on the NE-E side) and complementary shelterbelts (A3) otherwise. The shaping and sizing of such a green micro-system depends on the bioclimatic impact radius of the shelterbelts, which is usually 20 times higher than the average height of the planted area. Thus, a 20 m height shelterbelt can provide protection against wind and pollution over a distance of about 400 m, which means that the optimum area of an urban bioclimatic ensemble cell is about 15-20 ha, while the minimum recommended area is about 3-5 ha.
The Mobility Zone (B), used for parking and accessibility, is planted with deciduous trees especially with a high capacity to absorb the direct and indirect solar radiation, being characterised by a medium LAI(Leaf Area Index) level, a canopy density higher than 50-60% and wide tree canopies.
The Buffer Zone (C) includes green infrastructure features located close to buildings (C3) such as deciduous trees and shrubs on the SW facades (C1) and a high percentage of coniferous on the NE sides (C2), green roofs and green walls (lianas).
The Blue-green core (D), located in the centre of the bioclimatic cell, offers a refreshing microclimate and comprises a water feature (D2) for thermoregulation and mixed multi-layered vegetation (D1). It has an important recreational role, providing the best microclimatic conditions within the ensemble. Complementary, the bioclimatic cell includes two green ventilation corridors situated on the opposite direction of the prevailing winds to ensure the exchange of the air, especially in the summer or in foggy winter days and also to disperse the strong air currents from NE-E and W-SW.
BIOCLIMATIC GREEN NETWORK
The bioclimatic cell concept can be applied in planning as a repeatable module with variable shapes and sizes also at the extended scale of the metropolitan green spaces system in order to create bioclimatic green networks to provide a high level of comfort and security for the local communities. The implementation feasibility of the concept is higher especially in peri-urban areas, where territorial availability allows better development perspectives of green infrastructure. Also, the development of bioclimatic green networks can contribute to control the urban sprawl phenomenon and its environmental and social negative consequences.