Heat waves becoming more prominent in urban areas, research reveals
For past four decades, global warming has been amplified in cities, warns UCLA geographer
The frequency of heat waves has increased dramatically over the past 40 years, and the trend appears to be growing faster in urban areas than in less-populated areas around the world, a new study suggests.
“Our findings suggest that urban areas are experiencing a kind of double whammy — a combination of general climatic warming combined with the heat island effect, wherein human activities and the built environment trap heat, preventing cities from cooling down as fast as rural areas,” said Dennis Lettenmaier, a co-author of the study and a UCLA geography professor. “Everything’s warming up, but the effect is amplified in urban areas.”
Lettenmaier and his co-authors studied 217 urban areas across the globe and found that prolonged periods of extreme heat increased significantly in 48 percent of them between 1973 and 2012.
The results, which were published today in the journal Environmental Research Letters, show that about only 2 percent of those urban areas experienced a significant decline in heat waves. And the change was more dramatic at night: Almost two-thirds of the urban areas showed significant increases in the frequency of extremely hot nights.
“The fact that the trend was so much stronger at night underscores the role of the heat island effect in urban areas,” Lettenmaier said. “You have heat being stored in buildings and in asphalt, concrete and other building materials, and they don’t cool down as quickly as they would outside of the urban area. This effect was likely exacerbated by decreasing wind in most of the urban areas.”
The study is one of the first to focus solely on the extent of extreme weather in urban areas globally and to examine disparities between densely populated and less-densely populated areas.
Lettenmaier collaborated with researchers at the Indian Institute of Technology Gandhinagar, Northeastern University and the University of Washington. The team obtained daily observations for rain, air temperature and wind speed from the National Oceanic and Atmospheric Administration. The researchers identified about 650 urban areas with populations greater than 250,000 and then refined the list to the 217 locales based on the areas’ proximity to weather stations with complete weather records and NOAA data — most were located at airports close to urban areas. Although the researchers would have liked to have more data for urban areas in Africa, Lettenmaier said the report provides as close as possible to a representative sample of changing weather conditions in the world’s cities.
For each of the locales in the study, the researchers identified extremes for temperature, precipitation and wind, calculated heat and cold waves, and pinpointed individual extremely hot days and nights.
The study defined heat waves as periods in which the daily maximum temperature was hotter than 99 percent of days for the four-decade period and in which those temperatures were sustained for a consecutive period of six or more days. (The median length of heat waves was eight days.) It found that the average number of heat waves per year increased by over 50 percent during the period.
Of the five years with the largest number of heat waves, four were the most recent years for which data was available: 2009, 2010, 2011 and 2012. Urban areas in South America experienced the greatest increase in frequency of heat waves, followed in order by those in Africa, Europe, India and North America.
Researchers also found other striking examples of climate change within urban settings. Sixty percent experienced a significant decline in extreme windy days, 17 percent experienced a significant increase in daily precipitation extremes, and 10 percent experienced a significant increase in maximum annual precipitation.
“Urban areas make up a relatively small part of the global land area, but over half the world’s populations now live in them, so the trend is troublesome,” said lead author Vimal Mishra, an assistant professor of civil engineering at IIT Gandhinagar. “The combination of higher temperatures and lower wind in particular is not a good combination for human health and well-being. This should concern everyone.”
The increase in precipitation could damage cities’ infrastructure, which could also mean large economic losses, Mishra said.
Using a separate data set of 142 pairs of urban and non-urban areas, the researchers found that the frequency of heat waves grew 56 percent more quickly in urban settings than in surrounding areas that were less populated. Urban areas experienced 60 percent fewer extremely windy days than non-urban areas.
“In urban areas, buildings are disrupting the air flow, which affects not only the immediate area of buildings, but apparently the larger regional wind fields,” Lettenmaier said. “The reduction in wind may well be exacerbating the heat island effect.”
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Did somebody’s taxes seriously just pay for “UHI is real – especially at night”?
I spent last June sleeping with just a sheet, in Sydney. I wouldn’t try that in the bush even near Cairns!
Glad they could identify that mankind is simply using too much energy that is converted into heat in confined urban centres. Not enough to cause global warming – but enough with careful fudging of temperatures and careful limitations on the true effect and thus using incorrect adjustments for UHI to create the illusion of global warming.
Switching from one kind of fuel to another, say fossil to solar, has no effect upon the energy use and thus heat release at point of use – be it heating, air conditioning etc. or any domestic appliances.
So with the current way of assembling and ‘homogenising’ global temperatures a complete replacement of fossil with wind and solar will show no change at all to ‘global warming’. Only when correct adjustments for UHI are used and the constant manipulation of data to reduce earlier temperatures is brought to an end will we see an end to ‘global warming’. (That is unless we see temperatures fall in the next 20 years or so as the solar minimum has its predicted effect.)
As a random thought I wonder if anyone has ever run calculations, on a national scale, for the heat generated due to resistance by the distribution of electricity ? If heat release to atmosphere were ever to replace CO2 as the scientivist and political campaigning tool behind energy (and economic) policies then I suspect that the use of fossil fuels at or near the point of use would create lower heat energy release than remote generation (of whatever kind) distributed over massive distances. Just a thought.
A UCLA geographer takes one more step in the long walk back.
Of course the SurfaceStations project was cited in the literature review, right?
One aspect of the religion of Global Warming, is that it requires it’s adherents to believe that everything in the world is constant, except for CO2.
Thus, the idea that the cities they are studying have gotten bigger and more developed over the last 40 years just never occurs to them.
Wow, aren’t climate scientists clever!
On the subject of the role of urban areas on the temperature trends, see also
Montandon, L.M., S. Fall, R.A. Pielke Sr., and D. Niyogi, 2011: Distribution of landscape types in the Global Historical Climatology Network. Earth Interactions, 15:6, doi: 10.1175/2010EI371. https://pielkeclimatesci.files.wordpress.com/2011/02/r-344.pdf
We also conclude that most of these land use types (including urban areas) have a significant warming due just to a change in the vertical distribution of heat near the surface and not a deeper layer warming. This subject is discussed in
McNider, R.T., G.J. Steeneveld, B. Holtslag, R. Pielke Sr, S. Mackaro, A. Pour Biazar, J.T. Walters, U.S. Nair, and J.R. Christy, 2012: Response and sensitivity of the nocturnal boundary layer over land to added longwave radiative forcing. J. Geophys. Res., 117, D14106, doi:10.1029/2012JD017578. Copyright (2012) American Geophysical Union. http://pielkeclimatesci.files.wordpress.com/2013/02/r-371.pdf
Other papers include
Georgescu, M., G. Miguez-Macho, L. T. Steyaert, and C. P. Weaver (2009), Climatic Effects of 30 Years of Landscape Change over the Greater Phoenix, AZ, Region. Part I: Surface Energy Budget Changes, J. Geophys. Res., doi:10.1029/2008JD010745. http://www.agu.org/journals/pip/jd/2008JD010745-pip.pdf
Georgescu, M., G. Miguez-Macho, L. T. Steyaert, and C. P. Weaver (2009), Climatic effects of 30 years of landscape change over the Greater Phoenix, Arizona, region: 2. Dynamical and thermodynamical response, J. Geophys. Res., doi:10.1029/2008JD010762, http://www.agu.org/journals/pip/jd/2008JD010762-pip.pdf
Georgescu, M. et al 2012: Summer-time climate impacts of projected megapolitan expansion in Arizona. Nature Climate Change. doi:10.1038/nclimate1656. http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1656.html
and my post of this paper
https://pielkeclimatesci.wordpress.com/2012/08/16/new-paper-summer-time-climate-impacts-of-projected-megapolitan-expansion-in-arizona-by-georgescu-et-al-2012/
[Thank you for the (extended) list of papers, your time in researching and writing them, and your time responding here. .mod]
In this study, a city is a city. There is no mention of urban area. Are you suggesting UHI is greater in the middle of a 10-km square city than in a 5-km square city? Is there a critical area required for UHI to be significant?
Population Density.
UHI can never be measured quantitatively, there is no possible control. Attempts are made, such as a bicycle with recording thermometer passing linearly through city from a distant rural starting point.
The point is that urban thermometers are measuring the temperatures of underground steam pipes, or concrete, or air conditioner exhausts. What would the temperature of Manhattan Island be without the city??
It’s impossible to know. Is it 1C, 2C or 5 C in January or July???
Urban temps must be rejected in assessments of global temps.
When only rural temps are plotted, global warming is zero. The decade of the 1930s remains the warmest decade in the time of thermometers.
“…prolonged periods of extreme heat increased significantly in 48 percent of them between 1973 and 2012.”
Ch-ch-ch-cherry pick!
I didn’t see a link to the actual paper so here it is:
http://iopscience.iop.org/1748-9326/10/2/024005/article
The study period (1973-2012) coincides with a recognized warming trend globally. Indeed, 1973 essentially coincides with the end of a multi-decade cooling trend. Urban population (and therefore urban infrastructure) has increased tremendously since 1973. Therefore, finding anything other than an increase in urban heat waves would have been shocking.
In addition, the authors provide an important caveat when they state: “Increasing and declining trends in temperature extremes may be associated with natural climate variability, anthropogenic climate warming, and land use/land cover (Kiktev et al 2003, Alexander et al 2009, Min et al 2011b, Avila et al 2012, Coumou and Rahmstorf 2012). Here we simply report the aggregate effect on urban extremes and have not attempted to quantify their separate contributions.”
Simply an acknowledgement of UHI with no relationship to CAGW other than exaggerating it due to poor siting of measurement stations.
I have to wonder about Detroit’s local climate. That would seem to be a good test case for urban heat islands being amplified hypothesis.
Think about it.
Perhaps someone could suggest it to the researchers…
Well done to captain obvious. This has been covered to death on WUWT.
Give’em a break! The scamps just found out about UHI effect, got excited, then needed to tell everyone what they “discovered.”
Almost two-thirds of the urban areas showed significant increases in the frequency of extremely hot nights.
If you install underfloor heating the concrete floor becomes a thermal mass, buildings, concrete, more buildings, more concrete, nothing to do with CO2, it`s all to with population growth.
From 1950 to 1990, Melbourne, the capital city in the Australian state of Victoria, had a population increase from 1.5 million to about 2.5 million. Within the city (where the weather observations are taken), buildings progressively became higher and these blocked wind, cast shadows and, via the thermal properties of newer building materials, changed the daily patterns of heat flow. Other factors such as increased motor traffic and the increase in use of air conditioning in buildings probably also caused additional heat energy.
http://mclean.ch/climate/Melbourne_UHI.htm
“Urban areas make up a relatively small part of the global land area, but over half the world’s populations now live in them AND 3/4 OF THE WORLDS WEATHER STATIONS ARE SITUATED WITHIN THEM, so the trend is troublesome,” said lead author
The authors of this paper missed their calling, they should have been police detectives:
“Yes, the deceased committed suicide . . . by shooting himself in the head seven times.”
I’m encouraged by this “heat island” panic. The warmists have fallen back (hugely) to the only “confirm-able” effect of the much-touted but bogus “warmist” position. Yes – the cities are getting warmer, but not from CO2. Just concrete & infrastructure growth. And all the E-windmills and carbon sequestration plans in the world aren’t going to change it. Pity its wrecking the used-to-be science of climate studies.
“For past four decades, global warming has been amplified in cities, warns UCLA geographer”
Yes, poor people flock to citie, and have greater access to energy. In addition, there are more sewer systems now, removing standing water and reducing the amount of “latent heat” from evaporation.
Just reduce allowable energy usage by having rolling power blackouts, as happened years ago in California under Governor Gray Davis, eliminate the sewer systems, and you’ll get plenty of
case of cholera, malaria, a mass exodus from cities, and reduced warming in cities and the “paradise on earth” the UCLA geographer is striving for.