Natural process landscape plans: MICROCLIMATE

Planning for microclimate 

Air management can make places healthier and more comfortable. Air is the most public of all public goods. It passes from property to property and continent to continent with the greatest ease. Clean air is a pre-condition for good health. Polluted air is a serious cause of ill health. These points are agreed by all. But what can landscape planning do to improve air quality? A great deal. For cities, action can be taken at the macro- meso- and micro-scales. 2.14 In Stuttgart , air is encouraged to flow from cool hill-top areas, shown dark, down into the town. Stuttgart suffers from temperature inversions and becomes very hot in summer. Stuttgart 's air plan is the most famous example of a citywide climate plan [Fig 2.14]. Because of its valley location, the city suffers from temperature inversions which place a "ceiling" over the valley and trap polluted air. It becomes hotter in summer and colder in winter. Climatological studies revealed that the vegetated hills around the city were reservoirs of cooler fresher air. Building control regulations were used to protect the hills from urbanisation. A radial open space system was planned to function as a network of flow channels, ducting cool fresh air downhill to break the thermal "ceiling" over the city centre. At the meso-climate scale, individual streets and parks should be planned with regard to air quality. Air pollution and dust are severe problems. After developing asthma in my forties, I became very aware of air quality. On hot dusty days, walking into an exposed open space was like entering a battlefield. My lungs were under attack. Entering a cool shady space brought a great sense of relief. In unfavourable air conditions, I could hardly walk uphill. Drugs now ameliorate the symptoms but people who have not yet developed respiratory problems are, I think, comparatively unaware of air quality issues. The air quality requirements of open space vary according to climate and season. In hot arid climates, it is necessary to have shelter and shade: direct sun produces heat and glare; winds bring dust; pedestrians need narrow canopied streets; open space users need good tree-cover and, if possible, a dust-free breeze. In hot humid climates, the need for shade is equally great. In a damp climate dust is a lesser problem and humidity a greater problem, so outdoor space must be planned with regard to good ventilation. In temperate regions, air quality requirements are varied: sunny sheltered places for the winter; cool shady places for the summer. One of the more remarkable blunders of "form follows function" twentieth century city planning was the lack of attention given to air quality and climate. Corbusian cities with isolated blocks and wide streets were built all over the world, regardless of local conditions. Better air is one of the reasons why upper- and middle-income groups seek out "leafy suburbs" for their homes. At the microclimate-scale, significant air quality and climatic measures can be adopted. Simply put, cities should be swathed in vegetation. [Fig 2.15]. In future, the environmental impact question for developers will not be "can you get some planting into this space?" but "what special case can you make for not vegetating this wall or this roof?" The change of policy will produce the most significant difference between twentieth and twenty-first century cities. Twentieth-century cities were commonly described as "concrete jungles", despite being much more vegetated than their predecessors. Twenty-first century cities will be richly vegetated. Roofs will be clad in turf or other vegetation. Walls will have climbers. Car parking bays will have reinforced grass. Minor roads will be lightly vegetated so that they are porous to dust and water. Bare walls and roofs will become a sought-after rarity.