Protection and prevention

What is urban heat island?

An urban heat island (UHI) is a metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. The main cause of the urban heat island effect is from the modification of land surfaces, which use materials that effectively store short-wave radiation. As a population center grows, it tends to expand its area and increase its average temperature. The less-used term heat island refers to any area, populated or not, which is consistently hotter than the surrounding area.

A growing awareness of the issue of heat in urban areas – particularly as a result of the European heatwaves of 2003 and climate change projections, suggests that it is an emerging issue!

How it effects us?

Our warming climate has the potential to have adverse effects on our health and wellbeing. Temperature and humidity influence thermal comfort and for most people the optimal range for air temperature is between 20°C and 27°C and when relative humidity is from 35% to 60%. Record high temperatures and more frequent and severe heat waves will have a significant effect on many aspects of our everyday life. The direct impacts of heat exposure are well documented and include the heat-related illnesses of heat fatigue, exhaustion, heat rash, cramps , as well as heat stroke and sunstroke. Prolonged periods of high temperatures can interfere with daily activities and increase the potential for mistakes or injuries, reduce productivity, cause sleep deprivation and reduce physical performance. Motivation and general well-being can be detrimentally affected and studies have shown increases in aggressive and violent behavior. UHI can affect communities by reducing thermal comfort and play a role in heat-related illness and mortality. They also have detrimental effects on water quality and contribute towards escalating energy demand and costs, increasing air pollution and greenhouse gas emissions.Adapting to these impacts is critical. The key objective of adaptation to a changing climate is to reduce vulnerability by reducing exposure and sensitivity, and increasing adaptive capacity.

Table 1.Problems and symptoms caused by hot temperature

HOW CAN WE KEEP THE URBAN ENVIROMENT COOL?

Trees and other vegetation have an important influence on urban temperatures. We need to invest in natural spaces, tree canopy and innovative building design. Vegetation provides a natural cooling effect through evapotranspiration and absorptive and reflective processes. Trees are of particular importance as they can also provide shade that can reduce air temperatures by 10 to 50C. As vegetation and trees are removed from the landscape, their natural cooling effect is lost. Studies have shown that tree planting has been found to have the most effective cooling outcome. Trees can transpire significant volumes of water and it has been estimated that a mature tree can transpire up to 150 litres per day. In a hot dry location this produces a cooling effect similar to that of two air conditioners running for 20 hours 29.

Trees can reduce a building’s temperature by directly blocking radiation through windows and cooling the surrounding air, and can also keep the soil cool. Also we must reduce paved surfaces, buildings should be made from reflective materials, their hights should be limited and there should be enough spacing between them so that it won’t create urban canyons(narrow streets lined with tall buildings) and there would be free airflow ..

Recommendations :

Initiation of mechanisms to understand UHI vulnerabilities through appropriate studies and monitoring
Setting targets and measuring progress toward agreed tree canopy target
Accounting for health, environmental and social costs of tree removal
Increasing knowledge and communicating information about tree canopy effects
Establishing a cross-sector working group with key stakeholders from planning,development, environment, health and community sectors
Considering the value and importance of an Urban Forest Management Strategy forthe region
Establishing central government support for tree canopy management strategies to be developed at a local government level
Reduce urban heat build up and the need of air-conditioning by using reflective roofing materials("green roof"- coverd with soil and vegetation)

By analysing measurements, the researchers concluded that the number of trees planted for example along a pavement has a significant effect on wind speed. The street with the most trees produced the biggest reduction in wind speed compared to the control. Temperature, measured at a height equivalent to that of pedestrians, also varied considerably depending on street design. Tree-lined streets were cooler for most of the day thanks to shading, except for two to three hours before midday, when the street with the most trees was hottest. According to the researchers, this was probably caused by the low wind speed in this model. During mid-afternoon, all the tree-lined streets were around 7°C cooler. The researchers also found that trees on the sidewalks were more effective than trees in the middle of the street for reducing the temperature.

A developed range of urban characteristics that contribute towards better health outcomes for communities, includes links with biophysical environments through endorsement of:

A clean, safe physical environment of high quality
Stable and sustainable ecosystems
Access to a wide variety of experiences and social and cultural resources
Enabling connections with the cultural and biological heritage of the various urban inhabitants

Recognition of the potential benefits to health of retaining and restoring trees in the urban environment must be a key component of planning strategies and policy. Planning policy and development incentives can include:

Incorporation of trees in new and infill developments
Strategic placement of trees to provide optimal benefits for cooling and shade
Integration of energy saving techniques into land use and zoning activities
Encouragement of community-wide programs for tree planting in urban settings
Promotion of the benefits of trees through community education programs
Incentives for developers to retain and restore trees in subdivision plans
Promotion of specific UHI mitigation strategies by Local Governments and other public service sectors
Establishment of new and recognition of existing local by-laws to promote trees