2.1 Buildings in the UK Climate – Climate and Weather

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Main contributors to Module 2

Eric Parks and Andy Simmonds

 

The key objectives of Module 2 are:

  • to give a background in today’s climate across the UK
  • to give a background of how the UK climate might be in the future
  • and to consider the aspects of climates and microclimates that we need to keep in mind when designing a low energy retrofit

Module 2 consists of the following lessons:

Lesson 2.1 – Climate and Weather

Lesson 2.2 – Climate Change

Lesson 2.3 – UK Climates and Microclimates

Environmental conditions can vary significantly even within a small geographical area. In this module we look at some of the main weather-related factors to consider when retrofitting a property.

The climate is changing, and understanding all the possible consequences related to buildings in each region and individual locale is challenging. However, we aim in this module to give you a basic understanding of some key ideas and concepts that you will be able to apply to any retrofit.

 

By the end of this lesson you will have learned about:

  1. an introduction to climate and weather
  2. the relationship between climate and weather
  3. how our climate works (at different scales)

 

1. Introduction to Climate and Weather

Here, we start by looking at climate processes at different scales, starting with the global climate right down to the factors that create microclimates around our buildings.

Then we will identify issues at the macro- and micro-climate levels now and as the climate changes in the future (Lesson 2.2 and 2.3).

Later, in Module 5, we will study microclimates in more detail – describing the location, shape and typical characteristics of spaces or zones where microclimates affect structural and material condition or internal air quality.

Buildings are affected by climate at the following scales:

  • Global
  • National
  • Regional
  • Site
  • Building
The earth's atmosphere - a thin line
The earth’s atmosphere – a thin line

Above: This thin, delicate line (earth’s atmosphere) brings home why our climate is so vulnerable to greenhouse gas pollution of the atmosphere.

2. What is the difference between weather and climate?

We will be focusing mainly on climate at both the large and small scales. However, it is important to understand the main distinction between weather and climate – the time over which the conditions are experienced.

The Met Office offers the following description of weather and climate:

“Weather is how the atmosphere is behaving on a day to day basis including temperature, rain and wind. These can change hour by hour, day by day. Climate on the other hand looks at how the weather changes over a long period of time, typically over 30 years but sometimes over hundreds of thousands of years.
Climate is what you expect, weather is what you get”

Essential Reading: MetOffice_Guide_to_Climate_Science1

Optional Reading: A short video and further information about climate science is available here on the Met Office website: http://www.metoffice.gov.uk/climate-guide  

3. How Our Climate Works

We cannot know for certain the exact nature of our future climate. But we can base our assumptions in a sound understanding of the elemental workings of weather and climate.

We will start with the global scale and gradually move right down to the micro-climate scale within and around buildings, their components and layers.

The global climate is driven primarily by the following factors:

Solar radiation
This is the ultimate energy source that drives global climate through differential heating of land, air and water. The heated water, in turn, creates air currents / wind which drive weather patterns.

Solar radiation also heats at every level right down to an individual building. It is up to designers to control solar radiation – to provide heat in cold weather and to minimise overheating in hot weather.

Angle of Earth’s axis
Earth orbits around the sun in an elliptical orbit and with its axis tilted at 23.5 degrees off vertical – this creates the seasonal temperature differences:

  • When the northern hemisphere tilts away from the sun it is winter in northern hemisphere & summer in the southern hemisphere.
  • When the northern hemisphere tilts towards the sun it is summer in northern hemisphere & winter in the southern hemisphere.

Rotation of Earth on its axis
Global rotation induces the “Coriolis effect”. This effect is the rotation of Earth’s surface creating air movement that is generally clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere.

Other factors also influence how air and moisture moves across the globe. Some of these operate on a national or regional scale, and some can also be very localised:

Humidity
Moisture is present in the air – from bodies of water and precipitation. The lower the air humidity, the greater potential it has to take up and transport large amounts of moisture across the globe (and deposit that water somewhere else).

The surface over which air is moving will also influence the characteristics of the air flow (i.e. faster laminar or smooth flow typically occurs over plains or oceans vs. turbulent flow through urban, hilly or mountainous terrain).

On and off shore breezes
During the day, the dominant direction of wind will be on shore, and at night the dominant wind direction is off shore (see diagrams below).

Diagram to show air flowing onshore in the day and offshore at night
Diagram to show air flowing onshore in the day and offshore at night

Diurnal air flow patterns
These can also be found inland, amongst hills or mountains and valleys, for example. During the day, the wind flows up valleys. While at night the wind flows in reverse.

Diagram of wind direction in the daytime - uphill
Diagram of wind direction in the daytime – uphill
Diagram of wind direction at night - downhill
Diagram of wind direction at night – downhill

Changes in elevation
Height above sea-level affects temperature. It will be widely known that in situations similar to those shown above, the temperature will be highest at the lower points in the landscape and cooler at the tops of hills and mountains. Globally, the temperature falls by 6.5ºC for every 1000m increase in altitude.

Rain shadow effect

One further process to be aware of is the “rain shadow” effect. Moist air is cooled as it rises over high ground, leading it to deposit some of its moisture burden as rain or snow. The resulting dry air gives rise to a drier zone in the lee of the mountains – see diagram below.

Diagram to illustrate warm air rising over mountains and moisture falling as rain (leaving drier air in the lee of the mountains)
Diagram to illustrate warm air rising over mountains and moisture falling as rain (leaving drier air in the lee of the mountains)

All of the factors above are some of the fundamental and unchanging processes of climate that will operate, regardless of the severity of any changes in climate.

Activity

Keeping in mind the features of climate listed above, can you think of projects you have worked on or places you have lived where particular features were relevant? How did they affect the buildings?

Can you think of a very exposed location – and how this affected buildings in the area?

Note: Some of the quiz questions for this lesson are drawn from the Essential Reading list.

Summary

This lesson has covered:

  • The difference between climate and weather.
  • Climate processes that control the weather on different scales from global down to local.

 

Suggested reading

  1. A short video and further detail is available here on the Met Office website: http://www.metoffice.gov.uk/climate-guide  
Lesson tags: climate processes, global climate, local climate, local weather
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