Cities plan for the future

  Climate change and its amplification in large cities as urban heat islands is a great concern for all of us. These phenomenons are happening and have life threatening potential for many people in the developing world. As nations keep failing to agree on regulations for greenhouse gas emissions the future does not look great.

  However, on a city scale action is being taken much more effectively. National Public Radio aired a discussion about sustainable practices in Chicago and Salt Lake City in July of this year. Professor Brian Stone joins the conversation to present the science behind the necessesity to take measures against climate change in the city.

  The next few posts will explore the variety of action that is being taken to tackle climate change on an urban scale. To start with I want to warmly  recommend a fellow bloggers site. When thinking about a city that is at the forefront in the struggle against climate change and has already built a community which is closest to be considered 'sustainable', most of us would probably come up with Copenhagen. And indeed, Copenhagen has the ambitious goal to become the first carbon neutral capital in the world. The Danish capital wants to be carbon neutral by 2025. In addition to cutting carbon emissions, investment in renewable energies will be boosted and more trees planted around the city. All of these goals want to be achieved without impeding economic growth. The Copenhagen Design Week in 2011 presented many ideas. One of them deals with the expected population growth of 100 000 by 2025. New housing must be provided, Copenhagen does not go for the cheap and easy solution. The North Harbour is an excellent example of clever planning, it is one of the largest new urban development areas in Europe and will house 30 000 people. This city quarter is planned to be sustainable in every aspect. Other projects place family houses with attached gardens in inner city locations, watch this cnn report or go for a swim in Copenhagen's old industrial harbour.

  A very good resource on Green Copenhagen is provided by Anne Haugvaldstad in her Blog post Copenhagen: The First CO2 Neutral Capital. Follow her blog and you can also find out more about your personal climate impact and what you can do to stop the world from overheating.


Still to come...
How major cities around the globe work together to tackle climate change. Also, I want to run a special on my native Berlin and efforts to prevent climate change in the German capital.

To all Berliners:

source

London

  This time it is all about the city I currently live in: London. R.L. Wilby at his time at King's College London published a paper in 2003 on London's urban heat island which will be reviewed in this post. 

  The UK Climate Impacts Programme (UKCIP) predicts an increase in solar radiation and a decrease in cloud cover over southern parts of the UK. More global radiation (see post Urban Heat Island) will warm the land surface. The largest urban area inside the EU, London is located within this area. As I discussed in the last post, urban regions disproportionally warm a lot faster during heatwaves. Will hot days become an increasing problem in the UK capital famous for its fog and rain? 

  Over the summer of 1999 Wilby (2003) measured an average peak temperature difference between the British Museum and rural reference station Bracknell (30km to the west) of 3°C. London's Urban Heat Island (UHI) is strongest at night and it weakens with increasing wind speed. Figures 1 & 2 confirm a high night time (nocturnal) UHI which is strongest in inner city areas. Measurements representing Westminster (see Figure 1) were taken in St. James Park and therefore do not represent evening temperatures in built up areas which would be significantly higher as shown in Figure 2.  

Figure 1: Hourly variation in London's Urban Heat Island with increasing distance from the city centre (British Museum) to a rural site 30km to the west (Bracknell): Westminster (~2km), Hammersmith (~6km), Kew (~13km) and Heathrow (~26km), during six days in July and August 1999 & 2000, source: Wilby, R.L. (2003)

Figure 2: London Heat Island on 07/08/2003 at 9:30 pm, Inner city areas are significantly warmer than outer regions, source: Website 1

  London's UHI is strongest during summer where nocturnal averages reached 2.2°C in August of 1999. Whereas daytime UHI values were highest in December, however, their impact with 0.4°C on average is much less and can be attributed to anthropogenic heat production. From 1960 to 2000 the number of days with an UHI of 4°C or more (=intense UHI) has gone up by 4.4 days per decade. In the same time period the average nocturnal UHI during spring and summmer has gone up by 0.12°C per decade.

  How will London's UHI develop in the future? Wilby (2003) created a model. [For all of you who are keen to understand the model, here are the variables included: near-surface wind strength, vorticity, relative humidity and 850 mb geopotential height. This combination gave a correlation coefficient of R=+0.6 for observed vesus modelled values.] He then took the medium-high greenhouse gas emissions scenario by the IPCC for future atmospheric composition. Under this scenario, Wilby expects an increase in intense UHI days by 15 days per year in the 2080s compared to the 1961-2000 average. He also modelled an intensification of the UHI by +0.26°C on average. All of this is on top of an expected warming of 3.5-4°C in southern parts of the UK (UKCIP). Considering that the summer UHI is much stronger than in the winter, London's city centre could become a very hot place by the 2080s. If Wilby (2003)'s model is correct, Inner London will experience less night-time relief during heatwaves and reduced cooling of the already at times unbearably warm underground system.

And just imagine this lot...

...down here!

  On this note we should start thinking about techniques that can be incorporated into the built environment of a city to reduce the UHI. The next post will explore how cities start to take measures against further warming. An interview with this blog's compagnion Professor Brian Stone Jr. on Public National Radio will feature as well.

References

Wilby, R.L. (2003) Past and Projected Trends in London's Urban Heat Island, Weather, Vol. 58, pp.251-260

Website 1: http://climatelondon.org.uk/climate-change/heatwaves/ (accessed 14/11/2012, 17:05)

Urban Heat Island vs. Anthropogenic Greenhouse Effect

  This week's post is largely a review of chapter three in the book The City and the Coming Climate. Brian Stone introduces a study undertaken by his Urban Climate Lab to distinguish global warming due to greenhouse gases from the effects of the urban heat island.
 Stone (2012) takes us back to the year 1999. The Midwestern United States experienced a heat wave which led to the death of several hundreds of people. Figure 5 displays the temperature difference between the city of Chicago as well as the metropolitan area of St. Louis and their respective surrounding rural areas. The graph shows a mean difference of 1.1°C (2°F) to 1.7°C (3°F) for the week before the peak of the heat wave. During the last week of July 1999, the urban heat island intensified significantly. The average rural-urban temperature difference for St. Louis climbed to 2.8°C (5°F) and even up to 3.3°C (6°F) in Chicago for that week at the height of the heat wave. The temperature difference therefore doubled! Hence, urban areas have the potential to exacerbate extreme rural warming trends on the regional scale.

Figure 5: Urban-Rural Temperature Difference for 1999 Heat Wave, source: Website 1

  Since cities make up not more than 3% of the global land surface (Stone, 2012) the effect of the urban heat island is largely neglected in global warming research. An increase in atmospheric greenhouse gases has led to increasing global temperatures after the onset of industrialisation. Weather stations around the world confirm this trend. Many of these weather stations are located in major cities. They are statistically adjusted to mirror rural conditions, the urban heat island effect is therefore artificially excluded. However, focussing only on warming due to greenhouse gases greatly underestimates warming on a regional scale in metropolitan areas. As mentioned above urban centres exacerbate the underlying warming due to greenhouse gases. Stone (2012) identifies a lack of knowledge on urban climates.
  More people have died from heat stress than all other forms of extreme weather. It is therefore mandatory to get more data on the places half of the world's population lives in and where temperatures increase at a higher speed than anywhere else: our cities. Stone (2012) presents a study by the Urban Climate Lab in Atlanta, Georgia. The first problems arise when areas have to be identified as urban. Here, the night light intensity as measured from space (see Figure 6) is combined with population density data to distinguish an urban (bright lights) from a periurban (dim) and a rural place (dark).

Figure 6: Light Intensity at Night, source: Website 2

The urban heat island in the 50 most populous American metropolitan areas were monitored during a five-decade period, dating back to 1960 (see Stone, 2007 & Stone et al, 2012). Figure 7 gives an account of the rural (grey line) and urban (black line) temperature development from 1961-2010 in the US. The horizontal line at 0°F is the rural temperature average for this time period. The rural long term increase of about 0.8°C (1.4°F) is equivalent to global surface warming due to rising greenhouse gas concentrations in the atmosphere. The vertical distance between the grey and the black line represents the urban heat island. Stone et al (2012) have found an urban mean rate of warming over the 50-year period of 0.24°C (0.43°F) per decade. Rural areas warmed at a pace approximately one third less: 0.16°C (0.29°F) per decade. However 14 out of 50 cities did not show an intensifying urban heat island. These cities were largely older industrial cities with low sprawl indicies. Please read last week's post to find out about the relationship between a large sprawl of a city and its urban heat island. When only the 36 cities with a growing urban heat island are considered, the rate of warming is 0.31°C (0.56°F) and therefore double the rate of rural warming.

Figure 7: Urban-Rural Temperature Difference Over Past 50 Years, source: Stone et al (2012)

  The urban heat island effect in the majority of US metropolitan areas has the same warming potential as the rise in greenhouse gases. Major cities may therefore continue to warm twice as fast as rural areas. Heat-related deaths could still increase and will most likely do so in the megacities of the global south. An increase of concrete and asphalt in urban settings must be balanced with more green spaces to let the city breathe.

To look out for:
Beijing and Tokyo have been warming at rates five times greater than their rural surroundings in the past 50 years. In following posts I want to move away from the US for a bit and consider other continents and their urban heat islands. Architecture to counteract unwanted effects of urban warming are also still to come...

References

Stone, B. Jr. (2012), The City and the Coming Climate - Climate Change in the Places we live in. Cambridge University Press

Stone, B.Jr., Vargo, J., Habeeb, D. (2012) Managing climate change in cities: Will climate action plans work?, Landscape and Urban Planning, Vol. 107, No. 3, pp. 263-271

Stone, B.Jr. (2007) Urban and rural temperature trends in proximity to large U.S. cities: 1951-2000, International Journal of Climatology, Vol. 27, pp. 1801-1807

Website 1: http://mrcc.isws.illinois.edu/living_wx/heatwaves/heatwave1999.html (Midwestern Regional Climate Center, accessed 31/10/2012, 14:58)

Website 2: http://apod.nasa.gov/apod/ap001127.html (NASA, accessed 31/10/2012, 15:38)