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Section four .

You ' ll hear a talk on the subject of the urban landscape .

First , you have some time to look at questions thirty-one to forty .

Now listen carefully and answer questions thirty-one to forty .

Good day , ladies and gentlemen .

I have been asked today to talk to you about the urban landscape .

There are two major areas that I will focus on in my talk .

How vegetation can have a significant effect on urban climate ?

And how we can better plan our cities using trees to provide a more comfortable environment for us to live in .

Trees can have a significant impact on our cities .

They can make a city , as a whole , a bit less windy or a bit more windy , if that ' s what you want .

They can make it a bit cooler if it ' s a hot summer day in an Australian city , or they can make it a bit more humid if it ' s a dry inland city .

On the local scale - that is , in particular areas within the city - trees can make the local area more shady , cooler , more humid and much less windy .

In fact trees and planting of various kinds can be used to make city streets actually less dangerous in particular areas .

How do trees do all that , you ask ?

Well , the main difference between a tree and a building is a tree has got an internal mechanism to keep the temperature regulated .

It evaporates water through its leaves and that means that the temperature of the leaves is never very far from our own body temperature .

The temperature of a building surface on a hot sunny day can easily be twenty degrees more than our temperature .

Trees , on the other hand , remain cooler than buildings because they sweat .

This means that they can humidify the air and cool it - a property which can be exploited to improve the local climate .

Trees can also help break the force of winds .

The reason that high buildings make it windier at ground level is that , as the wind goes higher and higher , it goes faster and faster .

When the wind hits the building , it has to go somewhere .

Some of it goes over the top and some goes around the sides of the building , forcing those high level winds down to ground level .

That doesn ' t happen when you have trees .

Trees filter the wind and considerably reduce it , preventing those very large strong gusts that you so often find around tall buildings .

Another problem in built-up areas is that traffic noise is intensified by tall buildings .

By planting a belt of trees at the side of the road , you can make things a little quieter , but much of the vehicle noise still goes through the trees .

Trees can also help reduce the amount of noise in the surroundings , although the effect is not as large as people like to think .

Low-frequency noise , in particular , just goes through the trees as though they aren ' t there .

Although trees can significantly improve the local climate , they do however take up a lot of space .

There are root systems to consider and branches blocking windows and so on .

It may therefore be difficult to fit trees into the local landscape .

There is not a great deal you can do if you have what we call a street canyon - a whole set of high-rises enclosed in a narrow street .

Trees need water to grow . They also need some sunlight to grow and you need room to put them .

If you have the chance of knocking buildings down and replacing them , then suddenly you can start looking at different ways to design the streets and to introduce ...