Birmingham Urban Climate Laboratory: monitoring Birmingham’s urban heat island
The Birmingham Urban Climate Laboratory (BUCL) has recently been established by the University of Birmingham. BUCL is a high density, near real-time network of weather and air temperature sensors which are located in schools across the city. The long-term aim of the network is to identify, predict and promote adaptation to the impacts of urban heat and climate change on the population and infrastructure of Birmingham. But what is the ‘urban heat island effect’ and why are we interested in it?
The urban heat island (UHI) effect is a well-established phenomenon describing the elevated temperatures that are felt in towns and cities compared to rural surroundings which is particularly felt at night-time as the heat retained by artificial surfaces is slowly released keeping temperatures higher that in the countryside, as well as other impacts such as the reduced cooling effect of vegetation in urban areas, and the compounding effect of anthropogenic heat. UHI up to 8 degrees C have been felt in Birmingham, and cities the size of London have experienced temperatures in the order of 10 degrees C.
Q. Why is it important to find out how much warmer the city gets than the surrounding countryside?
Not only are the majority of the World’s population now living in cities [>50% world’s population now inhabit towns and cities (UN, 2009), with approx 70% expected to live in cities by 2050!], but the effects of extreme events (e.g. heatwaves, storms, floods, blizzards, hurricanes and tornadoes) are felt more strongly when they occur in populated environments. The severe European heatwave of 2003 was the warmest for 500 years, and was considered to be responsible for 14,802 and 2,045 excess deaths in France and the UK (most of these deaths were in urban areas and were a direct result of the increased temperatures experienced in towns and cities). Temperature of up to 38.5 degrees C was felt in the UK – and although these temperatures may be common place in other parts of the globe, this is unheard of in the UK. Indeed, the 2003 heatwave may be typical by 2040.
Even the heatwave we experienced in July 2013 – which saw an abnormally hot, dry and sunny July and temps up to 34.2oC – is thought to have resulted in up to 760 excess deaths. Urban heat can therefore have a big impact on hospital admissions, crime and anti-social behaviour, problems with transportation infrastructure such as roads and rails, as well as energy networks and of course there are the environmental and ecological impacts such as air pollution. However, if we can identify vulnerable areas of the city, then we can look to develop targeted mitigation strategies and improve our responses during such events.
Now I need to include a caveat here. I’m sure many of you are thinking ‘there are lots of other countries around the world that regularly deal with extremely high temperatures, so why can’t the UK cope?!’ Well, the problem in the UK – and in other countries with marginal, temperate climates who experience a whole range of weather and climate extremes – is that we simply aren’t used to these conditions so we aren’t adequately set up to deal with heatwaves. Our mostly old infrastructure needs updating and we need to develop appropriate adaptation and mitigations measures to help us cope with a warming climate and a climate with more extreme weather. But in order to do that we need a better understanding of these conditions and the impacts this has within urban areas.
Q. So what is BUCL?
BUCL is a high-resolution near real-time meteorological network of 25 automatic weather stations -collecting a whole range of variables including temperature, precipitation, wind direction, wind speed, pressure, relative humidity, solar radiation – and nearly 100 hundred air temperature sensors, the majority of which are located in schools across the region. In fact we think that this network could well be the highest resolution network within a city once it is complete.
BUCL is initially being used to explore air temperatures and urban heat across Birmingham, which will allow air temperatures to be mapped at a scale not previously possible. For example, up until recently, there was just one Met Office weather station within the Birmingham conurbation and one in a rural location just outside the city, with a city-centre site also added in 2010. One of the objectives of BUCL is to test models of the UHI, and have just a few stations isn’t sufficient to fully explore how temperatures vary across a large city which has variable land-uses.
Q. Were the sensors useful this summer during the heatwave?
Yes, and the heatwave event resulted in some really nice maps showing how temperatures varied across the city – we actually saw night-time UHIs of up to 6.5 degrees C between the city centre and areas around Sutton Park (a large urban park to the north of Birmingham), which demonstrates the cooling effect city parks and vegetation can have on air temperatures.
We have done some previous work using satellites to explore surface temperatures across the city and one of the future objectives is to use BUCL to explore relationships between the measured air temperatures and the surface temperature measurements derived from satellites – the idea being that if we can develop a robust relationship, we can use satellite observations of other urban areas to explore UHIs in more detail, without the need for such as dense network on the ground. The 25 weather stations we have located across the city collect a whole range of weather variables and we are looking to expand the network to include more rainfall measurements and air quality measurements in due course.
Q. What is the impact of urban areas on things like clouds and precipitation?
That is a very interesting question – however unlike for air temperatures, we are less clear about the precise effect urban areas have on clouds and precipitation, and to some extent it does depends on the type of rainfall. On one hand, cities are thought to increase precipitation, espectially convective precipitation, due to the impact of temperatures and the mechanical effect of the large buildings increasing convergence and convection, yet on the other hand, cities contain a large number of abnormally small man-made particles in the air, which although act as cloud condensation nuclei increasing the amount of cloud across cities, it is thought that this suppresses rainfall formation as the droplets don’t form into raindrops. So it is still a big research area and there may be a role for BUCL to play in this field in due course. There is certainly a role for BUCL to play in the observation of extreme rainfall events and the impact these events have on surface water flooding.
Q. Are urban areas and rural areas vulnerable to different impacts of climate change?
There are a lot of common impacts that both areas are vulnerable to but the fact is that urban areas are more vulnerable to a number of these. As we mentioned elevated temperatures in urban areas are felt more strongly, and this, coupled with higher relative humidity and less ventilation, means that cities are particularly uncomfortable – in contrast to this, during extreme cold weather, urban areas have slightly milder temperature so there is often less ice which is a positive effect for transportation systems in cities, but not for rural roads.
Flooding is another hazard which varies somewhat. The impervious surfaces in urban areas mean these areas are susceptible to surface water flooding as water can’t infiltrate through the ground and we get a lot of runoff into drains which can become inundated. So urban areas are often more susceptible to flooding caused by extreme precipitation events.
The key point here is that most people live in towns and cities, and there is more infrastructure located in urban areas, so any impact of climate change that occurs is going to be felt more strongly and by a greater number of people within urban areas, which is why we are focusing on these environments; essentially there is more to lose in these areas both in terms of society and the economy.
Q. Will concerns over urban heat grow as urbanisation spreads?
We’re already seeing awareness and concern for excess urban heat growing, certain industries, for example, the energy sector are concerned about the impacts on electricity transformers as temperatures increase and there is an increased demand for energy for air con units, so we’ve been doing some work with them to assess this issue, and I can only see this level of concern increasing with time, not only as we become more urbanised, but also as the effects of climate change become realised.