A very interesting NASA study has been reported entitled Keeping New York City “Cool” is the Job of NASA’s “Heat Seekers”
Thus study illustrates that the González et al tropical study that was discussed on the weblog on January 29th, also applies to midlatitude cities. The NASA study also shows that the deliberate modification of the urban landscape can alter the temperatures in this area.
Excerpts from the NASA report state,
“The ‘heat is on’ in New York City, whether it’s summer or winter. This is due to a phenomenon called the urban heat island effect that causes air temperatures in New York City and other major cities to be warmer than in neighboring suburbs and rural areas. And, in a big city, warmer air temperatures can impact air quality, public health and the demand for energy. ”
‘We need to help public officials find the most successful ways to reduce the heat island effect in New York. With ever-increasing urban populations around the world, the heat island effect will become even more significant in the future,’ said Stuart Gaffin, an associate research scientist at Columbia University, New York, and a co-author of the new NASA study. ‘The summertime impacts are especially intense with the deterioration of air quality, because higher air temperatures increase ozone. That has health effects for everyone. We also run an increased risk of major heat waves and blackouts as the heat island effect raises demand for electricity.’
“In large cities, land surfaces with vegetation are relatively few and are replaced by non-reflective, water-resistant surfaces such as asphalt, tar and building materials that absorb most of the sun’s radiation. These surfaces hinder the natural cooling that would otherwise take effect with the evaporation of moisture from surfaces with vegetation. The urban heat island occurrence is particularly pronounced during summer heat waves and at night when wind speeds are low and sea breezes are light. During these times, New York City’s air temperatures can rise 7.2 degrees F higher than in surrounding areas. ”
‘We found that vegetation is a powerful cooling mechanism. It appears to be the most effective tool to reduce surface temperatures,’ Gaffin said. ‘Another effective approach is a man-made approach to cooling by making very bright, high albedo, or reflected light, on roof tops. These light-colored surfaces, best made using white coatings, reflect the sun’s light and thereby, its heat. Interestingly, more area is available to create the lighter surfaces than to add vegetation in a city such as New York.’”
There are two cavaets to t his study, however. First, while the planting of vegetation can reduce the surface air temperature from what it otherwise would be, the addition of water vapor from transpiration can increase the humidity. This can make summer days more stressful as the heat index is elevated (e.g. see Segal, M. and R.A. Pielke, 1981: Numerical model simulation of human biometeorological heat load conditions - summer day case study for the Chesapeake Bay area. J. Appl. Meteor., 20, 735-749.).
Secondly, if the vegetated surface is darker, the solar insolation that is received at the surface will be greater than in the absence of this surface type. The result would be greater heat added to the surface, even though a fraction of the heat would be involved with the transpiration of water vapor. The need to account for the diverse consequences of land surface change for climate manipulation is discussed in Pielke Sr., R.A., 2001: Carbon sequestration — The need for an integrated climate system approach. Bull. Amer. Meteor. Soc., 82, 2021.
With these cavaets, however, the NASA study provides an effective summary of how we can positively alter the local climate for the benefit of society. The research group at the Lawrence Berkeley Laboratory directed by Hashem Akbari
is a leader in the investigation of such urban climate mitigation.
[...] 20;global temperature” estimates. Some professional level discussion on the topic is here. Trackback · [...]
Pingback by Common Sense Technology »Blog Archive » NASA finds “urban heat island” in New York City — January 31, 2006 @ 12:51 pm
Prof. Pielke; You may be interested in a similar example in Japan. As for UHI in Tokyo, a large city like New York, a kind of old wisdom has been tested by volunteer people based on an idea proposed by govermental officers. They sprinkled water (basically waste water but sufficiently clean one) onto paved road during hot summer days; this is called “Uchi-mizu” in Japanese (uchi = sprinkle, mizu = water); you can see a related HP in English (http://www.uchimizu.jp/05eng.html).
In 2003 summer, 430 thousand people reportedly attended this trial, and it was claimed that 1-2 deg C decrease in average temperature was observed in Tokyo. In 2005, they say more than one million people in Japan have attended.
It is intersting to note that when and where to sprinkle water was important to avoid uncomfortableness due to humidity increase. This is related to your advice.
The trial is not a thorough research of course, and may have secondary adverse effects as you have pointed out. But it may be interesting although being possibly dangerous and more or less hysteric.
Comment by Kiminori Itoh — February 1, 2006 @ 3:57 am
Much time an effort has been put into vetting the MSU data set over the past few years, and while the reported trend in MSU temperature has been increased, it hasn’t caught up to the surface trend. (Am I correct in my recollection that GCMs predict a greater warming trend in the upper troposphere than at the surface?) With all the recent discussions here and elsewhere about surface issues — the urban heat island, measurement site micrometeorology, site histpries, “local” biosphere changes, etc., it would appear that a critical evaluation of published surface temperature trends is now appropriate, especially in the context of the upcoming IPCC review of climate science.
This leads me to two questions, the first pragmatic and the second somewhat more “cosmic”:
– What is the surface trend in, say, the GISS data without the urban heat island correction? This must be easily available.
– What would be the impact on the climate discussion of a 20% or greater change (i.e., a significant change) in the surface temperature trend due to such considerations?
If the trend was to be increase the answer is easy, but what if the trend was to decrease?
Comment by S. Japar — February 1, 2006 @ 7:58 am
Dr. Itoh- Thank you for the information in comment #2 and the informative url.
On very local scales, people in Phoenix Arizona spray water from a garden hose on their patio floor surfaces (which are often concrete) to cool this small space. In this case, the added water vapor quickly blows away, but the surface of the patio is cooler, resulting in cooler air above, until the water completely evaporates.
Sprayers are also used in restaurants in such hot, dry climates to cool the air of the patrons as they eat.
Comment by Roger Pielke Sr. — February 1, 2006 @ 9:55 am
Sorry that I am just replying to this older posting on UHI …
2 comments:
Re: “vegetative surface is dark …” Typical plant albedoes are indeed probably generally low and probably close to dark pavements, however the low temperatures we have *observed* on NYC vegetated surfaces proves that the latent heat cooling more than compensates for the additional solar absorbed on the dark plants. In my recent green roof modeling, I found that latent cooling was up to 8 times greater than sensible cooling.
Further in some recent UHI “reconnaissance” work we have been doing around NYC, we find that light colored surfaces are not dramatically cooler than darker surfaces. In reality, considering the soot, weathering and texture of typical lighter colored urban surfaces, their albedo is probably not that great.
The only time we have seen impervious surfaces ever cooler than vegetated surfaces is in the early morning, with dense materials, that have cooled at night and take a long time to heat up …
On the question of surface temperature trends with and with out UHI included, we calculated this for NYC and find that, excluding UHI, NYC’s 100 year temperature trend has been +.109 deg C per decade. By contrast the trend for Central Park (which was not included in the last number) is .14 degrees per decade. Therefore the uhi warming seems to be roughly about .031 deg/decade, or about a third of the non-uhi/climate warming …
Comment by Stuart Gaffin — June 13, 2006 @ 12:46 pm
First, if there is sensible “UHI” in cities, what makes us think there is none on rural highways, bldgs, bared land, etc. and it is not just in “urban” areas?
Second, am I missing something or is there a sign error in Stuart’s post?
Third, how much of the flora “darkness” is due to biomass production and evapotranspiration? That’s actually a loaded question, as I’m sure every species is different.
Comment by Steve Hemphill — June 14, 2006 @ 5:51 pm
Stuart- Thank you for your comment.
The use of temperature by itself is an incomplete measure of heat. This is clearly illustrated by lower air temperatures over grassy areas on sunny clear days, as constrasted with concrete. Even with the lower albedo, the grass can have a lower temperature since a large fraction of the heat is contained in the absolute humidity of the air over the grass. This absolute humidity will typically be higher then over the concrete.
Moreover, the difference in heat capacity between the soils of the grass area, and the concrete will also complicate the ability to relate the temperatures at each site to heat.
Please see Pielke Sr., R.A., C. Davey, and J. Morgan, 2004: Assessing “global warming” with surface heat content. Eos, 85, No. 21, 210-211
http://blue.atmos.colostate.edu/publications/pdf/R-290.pdf
for an overview of this issue.
Your assessment of the UHI needs to include both temperature and absolute humidity.
Comment by Roger Pielke Sr. — June 15, 2006 @ 10:36 am
[/ignore]
sigh…so much malinformation, so little time.
One tends to suspect this malinformation must be willful, as this has been explained to you so many times:
First, if there is sensible “UHI� in cities, what makes us think there is none on rural highways, bldgs, bared land, etc. and it is not just in “urban� areas?
Because we’ve studied it and know the effects of soil and plants on temp. A visit to the library will help you speak to the issue.
Second, am I missing something or is there a sign error in Stuart’s post?
Why don’t you point it out rather than trying to sow doubt?
Third, how much of the flora “darkness� is due to biomass production and evapotranspiration?
This is gobbledegook.
Albedo is a measure of reflectivity.
“Flora” is dark because of the light it absorbs. Vegetation has a relatively dark albedo because of the fact that it is green.
So, landcover changes affect albedo, and plowed bare earth has a higher albedo, relatively cooling the area. Darker albedos due to vegetation affect temps, which are moderated by ET and water vapor. This is simplified, of course, but should suffice to point out the errors in the implied argument above.
[ignore]
Best,
D
Comment by Dano — June 15, 2006 @ 10:44 am
I have one further comment on the UHI issue. The use of parks within urban areas to assess “rural” effects” is not appropriate. The temperature profile that is altered as air flows over urban areas of a city will also flow over embedded parks. Thus Central Park is still significantly influenced by the adjacent urban landscape of New York.
Comment by Roger Pielke Sr. — June 15, 2006 @ 3:02 pm
re: Comment 9.
Note in our UHI study we did *not* use Central Park (CP) to “assess rural effects” - on the contrary we specifically excluded it (& other inner city stations) from the 23 stations outside the NYC metro area, to assess UHI.
In my prior comment # 5, I was quoting the 20th century Central Park warming as an indicator for urban warming, not rural, because it has such a nice long record from the mid-Manhattan vicinity. However as such, because the CP station is in the middle of heavily vegetated area it is no doubt underestimating urban warming experienced in the nearby dense Mid-town area. Nevertheless, Central Park too shows UHI unequivocally when compared to the 23 stations well away from Manhattan’s core.
Comment by Stuart Gaffin — June 19, 2006 @ 1:10 pm
Stuart-Thank you for the prompt clarification.
My comment was specifically with respect to the claims such as those made in the paper Peterson, T, 2003: Assessment of urban versus rural in situ surface temperatures in the contiguous U.S.: No difference found. J. of Climate (pages 2941-2959). Peterson used park areas embedded within urban areas as part of his study.
Comment by Roger Pielke Sr. — June 19, 2006 @ 2:13 pm
Roger,
what you say in comment #11 is unbeliveable.
But, I know, you are right (sic!).
Comment by Paolo M — June 19, 2006 @ 2:53 pm