Lesson objectives: To examine the other symptoms of urban stress Developed / Developing Compare and contrast the problems

Urban stress The social, economic and environmental problems created in an urban area as a result of urban growth

Key terms Urban sprawl Urban heat island Microclimates Commuting Infrastructure

P305 – problems of MEDC / LEDC cities

Impacts of the urban heat island UHI: an urban area that is significantly warmer than its surrounding rural areas due to human activities. 

Urban Heat Islands

Urban Areas tend to produce heat Due to all the people, buildings, cars etc cities ‘give off’ heat. They are usually warmer than surrounding rural areas

The East Coast of the USA The East Coast of the USA.. You can clearly see the urban areas on this thermal map.

Urban Areas may have different ‘Microclimates’ within them What is a microclimate?? ‘A microclimate is a local atmospheric zone where the climate differs from the surrounding area. The term may refer to areas as small as a few square feet (for example a garden) or as large as many square miles (for example a valley area)’ In English… some places near to each other may have slightly different weather conditions.. This usually means that the temperature and wind conditions may be different in certain parts of a city.

A city will usually have different weather than the surrounding rural areas. The weather is obviously not uniform across the country, and there can be big differences in just a short distance. By building large cities in what once was a rural setting, we can disturb the weather and give the location its own micro-climate. This is called an urban heat island. So, in theory, the further you move away from the rural area the weather should gradually change. Likewise, as you travel out of the city the weather should become similar to that of the rural areas surrounding the city

How could different places in a city have different weather? Usually it is hotter near the city centre..

Other factors influencing UHI intensity Weather conditions Topography and hydrology Population size and density Economic development Building and street design Land surface cover Anthropogenic heating Air pollution

Is it because of all the buildings? The buildings and roads act like giant storage heaters. The large amounts of concrete, asphalt and bricks used in buildings and roads 'soak up' heat in the daytime and store it. The energy is then released during the night time. Also in the morning the city will have the stored heat so the sun starts warming the city from a higher ‘starting point’ than the rural area

What else might have an influence? A lack of natural environment in the city that absorbs less heat than buildings, such as open spaces, has an impact. Heat released from vehicles and places like factories also add to the heat problem.

In some places the presence of water and the ground surface has an effect.. Another reason why large towns and cities are generally warmer is due to decreased amounts of evaporation. In the countryside there is more water. As the water evaporates the process of changing from a liquid to a gas uses latent heat, which cools the surroundings. Road surfaces and building materials such as brick and concrete absorb heat during the day and act like giant storage heaters releasing it slow at night. . You can easily feel this by standing on a black tarmac road on a hot summer's day, and then walking onto some parkland. You will immediately feel cooler. Dark colours absorb more heat than light colours.

The buildings can have an additional role to play.. Heat energy is released from industrial and domestic buildings (e.g. through poorly insulated roofs, doors and windows). An ordinary incandescent light bulb, like those still used in many homes, only uses 10% of the energy it requires for light and gives the rest off as heat. Glass buildings and windows reflect large amounts of solar radiation into the surrounding air.

And some more complicated ones… Water attracting (hygroscopic) pollution particles in the air act as nuclei for condensation. These promote the formation of clouds and smog which can trap heat in the lower atmosphere. In many cities there may be relatively small amounts of liquid water. Less heat energy is therefore used up in evaporation.

Some places in cities may be windier than the surrounding rural areas and other parts of the city. Tall buildings provide shelter from the fast moving winds in the upper atmosphere. At the same time however buildings can disturb the pattern of airflow. Fast turbulent winds can be funneled between buildings creating wind that swirls up dust and litter making walking between buildings difficult.

The ‘Aspect’ may be a factor If a surface is exposed to the sun all day it will absorb energy and ‘give off’ heat. Areas that do not face the sun very much or even some that never seethe sun will therefore be cooler. This is assuming that all other things are the same.

Sometimes even the amount of rain might differ.. As well as being warmer urban ecosystems often have more rain. atmospheric pollution from cars and buildings can lead to more cloud cover which in turn could lead to more rain The warmer temperatures can also lead to the formation of convection currents and strong thermals. These can help both to form and strengthen thunderstorms leading to higher rainfall both in the urban area and downwind of it.

Impacts of UHI Cause Impact Explanation Higher levels of ozone and particulate matter So: Therefore Therefore increased human discomfort Disease such as vector and water bourne diseases Loss of energy by air conditioning Heat stress and illness Degradation of tarmac and other materials

So what? Write a paragraph to explain why UHIs are of concern: Consider 1) increasing rates of urbanisation 2) increasing affluence 3) global warming 4) positive feedback

Where am I? I am an urban area I have a population density of 130,000 per km2 According to the Guinness World Records I am the busiest district in the world I am located at 22.3225° N, 114.1706° E

What other factors of urban stress? Housing, social problems and inequality (crime), violence, noise, over crowing, loss of green space