Satellites define the surface urban heat island (UHI) for 419 global cities
February 25th, 2013 by Warwick HughesMatt Ridley’s page “The greening of the planet” lead me to the work of Professor Ranga Myneni of Boston University. A page listing his publications has a link to this 2012 paper – “Surface Urban Heat Island Across 419 Global Big Cities”.
Peng et al., 2012 Surface Urban Heat Island Across 419 Global Big Cities, Environ. Sci. & Tech., Environ. Sci. Technol., 2012, 46 (2), pp 696-703, DOI:10.1021/es2030438
ABSTRACT: Urban heat island is among the most evident aspects of human impacts on the earth system. Here we assess the diurnal and seasonal variation of surface urban heat island intensity (SUHII) defined as the surface temperature difference between urban area and suburban area measured from the MODIS. Differences in SUHII are analyzed across 419 global big cities, and we assess several potential biophysical and socio-economic driving factors. Across the big cities, we show that the average annual daytime SUHII (1.5 ± 1.2 °C) is higher
than the annual nighttime SUHII (1.1 ± 0.5 °C) (P < 0.001). But no correlation is found between daytime and nighttime SUHII across big cities (P = 0.84), suggesting different driving mechanisms between day and night. The distribution of nighttime SUHII correlates positively with the difference in albedo and nighttime light between urban area and suburban area, while the distribution of daytime SUHII correlates negatively across cities with the difference of vegetation cover and activity between urban and suburban areas. Our results emphasize the key role of vegetation feedbacks in attenuating SUHII of big cities during the day, in particular during the growing season, further highlighting that increasing urban vegetation cover could be one effective way to mitigate the urban heat island effect.
Posted in Urban Heat Islands | 9 Comments »
February 25th, 2013 at 2:35 pm
Good find Warwick. Doesn’t Jones at UEA-CRU still deny there is any significant UHI?
February 25th, 2013 at 5:00 pm
Jones and the IPCC have pretty much stuck to this mantra –
“… urban effects on 20th century globally and hemispherically averaged land air temperature time-series do not exceed about 0.05°C over the period 1900 to 1990…”
Although in 2008 there were these papers on Chinese data – but I am not aware that any reality is filtering through to IPCC Exec Summaries yet. It will be a colossal backflip for them all to admit 25 years of errors.
History made as Jones et al 2008 paper admits huge urban warming in IPCC flagship CRUT3 gridded data over China
Chinese climate scientists tactfully tell the IPCC that surface air temperature (SAT) trends over north China include a large component of urban warming
I have several posts over the years pointing out huge differences in surface & satellites over Eastern China.
For example -
Surface minus satellites – some differences look political
February 25th, 2013 at 7:48 pm
The other day on the BBC the Met Office weather forecaster said:-
“Minimum temperatures in the towns will be -5 degrees and -8 in the countryside”.
Says it all, really!
UHI? Nah, it don’t exist. /sarc off
February 26th, 2013 at 8:57 am
The issue with UHI is whether it has a significant trend, and thus contributes to increasing global temperatures.
Once an area has been urbanized, there is generally not much change in evapotranspiration or albedo (with a notable exception below). The main effects on UHI temperature trend are increasing geographic area of urbanization (larger urban areas and the resultant increasing proximity of non-urban stations to urban areas) and increasing Urban Canyon Effect from increasing urban density (higher buildings).
In hotter drier cities increasing urban density results in increasing temperatures from decreased irrigation and evapotranspiration, with some albedo effect. We see this here in Perth, where most of the 1/4 acre lots within a few kms of the CBD have been converted from one house and a garden to 2 houses and not much garden.
Waste heat from increasing energy use per unit area also contributes to increasing urban temperatures, but its not clear how much.
February 26th, 2013 at 9:03 am
Thank you, Warwick. The community needed a paper like this, though I’ve only skimmed it so far, but certainly after a couple more reads it will be publicised as appropriate.
Possibly, I’ll be contacting Mosh privately to see if there’s a consequence that BEST would like to publicise also.
I wish I’d had the foresight you showed at Tasman ca. 1992. This looks like another example of early warning from you, providing some ways to redress the way I failed to follow up adequately way back then.
February 26th, 2013 at 11:44 am
This is a good review of UHI, concentrating on albedo. Note the size of the cloud and aerosol albedo effects, as much as 8% higher versus rural areas. Reduced urban aerosols over the last 50 years has likely produced a significant UHI warming trend.
lup.lub.lu.se/luur/download?func=downloadFile&recordOId=1856904&fileOId=1856935
It appears in the paper above they are measuring land surface temperatures (by satellite) and so are missing these significant urban aerosol effects on albedo.
February 26th, 2013 at 4:35 pm
I live in adelaide which as far as city layout is probally unique in the world.
The central business district (10 square kms) is surrounded by parklands ( 30 square kms) ,
which is then surrounded by the metropolitan area ( 750 square kms)
I used to ride my motorbike every morning across the 3 zones i mentioned into the CBD.
It was substantially cooler in the parkland zone.
My seat of the pants temp gauge would suggest many degrees cooler
February 26th, 2013 at 4:41 pm
Agree the history of aerosols is interesting indeed.
A decade or so ago I worked up some pages on air quality. At that time there was frequent publicity about air pollution – not much is heard now – climate is the big yakking point.
This page on Melbourne data has a few graphics showing how our AQ has improved over the decades in the late 20th Century – if you scroll to the bottom you see how Melbourne visibility has improved since 1955 – and then below that a graphic showing 400 years of London AQ by Bjorn Lomborg.
I feel sure AQ must have been bad pre-WWII in our cities but little is said about that.
February 28th, 2013 at 6:30 am
You may be interested in my study of inland tropical cities in the appendix of my latest paper linked below, but first you need this outline …
Prof Nasif Nahle has done studies on backradiation in his paper
principia-scientific.org/publications/New_Concise_Experiment_on_Backradiation.pdf
which I cited a year ago in my paper
principia-scientific.org/publications/psi_radiated_energy.pdf
Nasif is one of several physicists and professors of other disciplines on the team at Principia Scientific International all of whom recognise fallacies in the AGW conjecture.
You need to see the big picture to understand the relative insignificance of backradiation, as explained towards the end of my latest paper
principia-scientific.org/publications/PROM/PROM-COTTON_Planetary_Core_and_Surface_Temperatures.pdf
1. The thermal gradient (AKA “effective lapse rate”) is pre-determined by the force of gravity, the weighted mean specific heat of the gases in a planet’s atmosphere (at that altitude) and the degree of intra-molecular radiation which, in the case of Earth, is somewhat dependent on the percentage of water vapour which, as is well known, makes the gradient less steep.
2. The overall level of the plot is established by the autonomous propensity for there to be radiative equilibrium with incident Solar radiation. The area under the curved plot of outward radiative intensity thus has a propensity to remain constant if the gradient alters. So extra water vapour makes it less steep by lowering the surface end and raising the tropopause end.
3. The surface temperature can then be calculated by extrapolation of the thermal plot of temperature against altitude in the troposphere. The temperature can be derived using SBL from the values of radiative flux at each altitude from (2). The higher the tropopause, the greater the distance over which the temperature can rise, this explaining why Venus is much hotter than Earth.
4. The mechanism whereby the thermal plot is maintained involves the absorption of energy originally from the Sun (both in downwelling and upwelling radiation) which is then dispersed in all directions over the thermal plane, in order to maintain thermodynamic equilibrium, in accord with the requirements of the Second Law of Thermodynamics.
5. The thermal plot continues its upward climb more steeply in the crust (due to lower specific heat) but far less steeply in the hottest regions of the mantle because specific heat increases significantly with increasing temperatures.
6. Heat creep, as described in (4) allows thermal energy to enter deeply into the subsurface regions and, eventually, to support core temperatures and provide energy which can contribute to that in volcanoes and thermal springs and vents.
7.The surface warms temporarily during the day and then both radiative and non-radiative processes slow its rate of cooling, but there is a limit to such cooling due to the underlying very stable thermal plot of temperature against altitude or underground depth. This is why the base of the atmosphere does not continue cooling at a fast rate all through the night. The force of gravity redistributes absorbed energy in such a way as to provide a supporting temperature at the boundary of the surface and atmosphere, and even at the boundary of the mantle and core.