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Are the effects of urban urban heat islands more intense in downtown areas or are they equally noticeable throughout sense cities? Can other factors make the downtown area actually cooler? Although I assumed downtowns would be warmer, I found an example from Chicago that shows otherwise. Using data from US Climate Data, the downtown Chicago climate station averages 49.65 degrees during the 1961-1990 time period, the last available time period for that site. Midway Airport averaged 50.5 degrees during the same period (SERCC Nowdata). The lake clearly cooled downtown during the summer by about 2 degrees, but the reverse was not true during the winter. Also, can urban heat islands cause more precipitation in the citty, or is the effect limited to temperature?
Are the effects of urban urban heat islands more intense in downtown areas or are they equally noticeable throughout sense cities? Can other factors make the downtown area actually cooler? Although I assumed downtowns would be warmer, I found an example from Chicago that shows otherwise. Using data from US Climate Data, the downtown Chicago climate station averages 49.65 degrees during the 1961-1990 time period, the last available time period for that site. Midway Airport averaged 50.5 degrees during the same period (SERCC Nowdata). The lake clearly cooled downtown during the summer by about 2 degrees, but the reverse was not true during the winter. Also, can urban heat islands cause more precipitation in the citty, or is the effect limited to temperature?
Chicago may not be the best example for UHI impacts as it is very heavily influenced by the temperature of Lake Michigan during different seasons.
Also there is 1981-2010 data for Northerly Island which is in downtown right on the lakefront.
Annual Mean is 51.9F
Here is MDW's data which is located 9 miles away from the lake in a heavily urbanzied part of Chicago.
The UofC which is only 1.5 miles from the lake has similar temps with that of MDW.
Last edited by chicagogeorge; 04-03-2017 at 07:53 AM..
Chicago may not be the best example for UHI impacts as it is very heavily influenced by the temperature of Lake Michigan during different seasons.
Also there is 1981-2010 data for Northerly Island which is in downtown right on the lakefront.
Annual Mean is 51.9F
Here is MDW's data which is located 9 miles away from the lake in a heavily urbanzied part of Chicago.
The UofC which is only 1.5 miles from the lake has similar temps with that of MDW.
The reasons you state are some of the reasons I chose Chicago; I wanted to see if there were exceptions to some of the widely held opinions about heat islands. Does Northerly Island report precipitation and snowfall? I knew it existed but I didn't use it because it lacked this info and I could only find data for a ten year period. It is also about a mile from the center of downtown and completely surrounded by water, so it seems have much more lake influence than the rest of the city. However, as you said Midway is almost 10 miles away from the downtown and nowhere near the lake. I have yet to find a station that accurately portrays downtown and the north side of the city.
This is the data 1961-1990 from the downtown station I referenced.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann
32. 34. 43. 55. 65. 75. 81. 79. 73. 63. 47. 36. 56.8
18. 20. 29. 40. 50. 60. 66. 65. 58. 47. 34. 23. 42.5
This is noticeably cooler than MDW, even being in the center of downtown. While the lake would have an effect, I would think the annual mean temperature should be virtually the same. This is why I wondered whether a dense urban neighborhood like MDW could actually have more heat island than center city. Some months, such as May and June are about 5 degrees cooler than MDW, but the opposite is not true in the fall. The only time MDW is clearly colder is early winter lows. I really wish snowfall statistics were provided; I am curious if the lakeside locations get significantly more than the airports.
Another reason I chose the city is I am probably moving there next year. I have always heard how cold and snowy is in the winter, but have recently seen the statistics weren't as cold as I expected and the coastal north side and downtown were supposedly even warmer. One of the things I look for in a city is a real winter with a lot of snow. I was hoping for a place with 2-3 months of at least some snow cover (even if it is not always measurable), and was curious if Chicago could provide that most years.
The reasons you state are some of the reasons I chose Chicago; I wanted to see if there were exceptions to some of the widely held opinions about heat islands.
I see
Quote:
Does Northerly Island report precipitation and snowfall?
No, not to my knowledge.
Quote:
I knew it existed but I didn't use it because it lacked this info and I could only find data for a ten year period.
NOWData only had records for that site going back to 2005. NCDC however has 30 years of data for Northerly Island online, but I believe it combines older data from when the station was Meigs Field and now, so it has been moved around.
Quote:
It is also about a mile from the center of downtown and completely surrounded by water, so it seems have much more lake influence than the rest of the city. However, as you said Midway is almost 10 miles away from the downtown and nowhere near the lake. I have yet to find a station that accurately portrays downtown and the north side of the city.
This is the data 1961-1990 from the downtown station I referenced.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann
32. 34. 43. 55. 65. 75. 81. 79. 73. 63. 47. 36. 56.8
18. 20. 29. 40. 50. 60. 66. 65. 58. 47. 34. 23. 42.5
This is noticeably cooler than MDW, even being in the center of downtown. While the lake would have an effect, I would think the annual mean temperature should be virtually the same. This is why I wondered whether a dense urban neighborhood like MDW could actually have more heat island than center city. Some months, such as May and June are about 5 degrees cooler than MDW, but the opposite is not true in the fall. The only time MDW is clearly colder is early winter lows. I really wish snowfall statistics were provided; I am curious if the lakeside locations get significantly more than the airports.
High temps closer to the lake will be cooler in the spring and summer. Lows will be higher in the winter. High temps are very different during the winter..
ORD has lower minimum temps than both MDW and Northerly as well as UofC demonstrating that ORD is more like a Northwest suburban station and not as representative of the city itself. The highs are very similar to MDW and UofC
Probably the most urban station that I know is located at DePaul University. Unfortunately like UofC theyd don't publish data. I recall during the summer of 2012, WGN said that the minimum at that site was 86F/30C which was a few degrees higher than all other stations.
Quote:
Another reason I chose the city is I am probably moving there next year. I have always heard how cold and snowy is in the winter, but have recently seen the statistics weren't as cold as I expected and the coastal north side and downtown were supposedly even warmer. One of the things I look for in a city is a real winter with a lot of snow. I was hoping for a place with 2-3 months of at least some snow cover (even if it is not always measurable), and was curious if Chicago could provide that most years.
You likely won't see 2-3 months of continuous snow cover....
For areas moderated by water, UHI will only appear with night-time lows relative to surrounding areas farther inland; the effect becomes neutralized, even reversed, during the daytime summer heat.
This is a data table I created by taking the data from the previous stations in the Loop and applying the average temperature changes exhibited by other stations in the area since then. Based on this data, downtown and the lakefront appear to be about five degrees lower during summer days than MDW or ORD, whereas Northerly Island only shows a difference of about one degree. Based on my experiences in the city, this table seems more accurate. If the Northerly Island data is correct, than downtown must have warmed far faster than the surrounding area, which makes little sense because this was not true in the old data prior to 1970. Also, downtown has long been developed and therefore had the UHI whereas other areas are only beginning to receive UHI. When comparing this data with another coastal station such as Kenosha, downtown appears to exhibit typical UHI. The highs are only slightly higher in the city, but the lows are a few degrees colder in Kenosha. Does the table appear close to accurate to you, chicagogeorge? Is there something I am missing? I am currently working on precipitation and snowfall statistics.
Last edited by brianpmcdonnell17; 04-20-2017 at 08:29 PM..
[quote=Texyn;47733545]For areas moderated by water, UHI will only appear with night-time lows relative to surrounding areas farther inland; the effect becomes neutralized, even reversed, during the daytime summer heat.[/QUOTE
Very true.
For example, here in Toronto, what you mentioned holds true.
Average day time highs (except in winter) are slightly warmer out at the airport,
than downtown. Only the lows are warmer downtown.
Kew and Northolt are in frost hollows and Hampstead is elevated. St James's Park data is behind a paywall, probably has similar highs to the London Weather Centre but slightly cooler winter lows. Olympic Park has warmer minima than Heathrow, but has only been recording for 6 or 7 years. There are not enough weather stations in the 'normal' parts of London.
Given the time of year the data were recorded and the conditions at the time, the map probably represents the maximum UHI effect. Nevertheless, using it verbatim it looks like within about 15km of the centre of town the nocturnal effect is 2°C or higher. If you do the math you'll see this area probably includes about 50% of the population of London metro.
This paper shows a comparison between St. James Park and a site in Wisley (30km southwest of London). The effect of the UHI is greatest in summer, smallest in winter. According to these data the effect is considerably smaller than that suggested by the above map; this likely reflects the "ideal" UHI conditions when the map data were measured and the fact that St. James Park is, in fact, a park.
This is a data table I created by taking the data from the previous stations in the Loop and applying the average temperature changes exhibited by other stations in the area since then. Based on this data, downtown and the lakefront appear to be about five degrees lower during summer days than MDW or ORD, whereas Northerly Island only shows a difference of about one degree. Based on my experiences in the city, this table seems more accurate. If the Northerly Island data is correct, than downtown must have warmed far faster than the surrounding area, which makes little sense because this was not true in the old data prior to 1970. Also, downtown has long been developed and therefore had the UHI whereas other areas are only beginning to receive UHI. When comparing this data with another coastal station such as Kenosha, downtown appears to exhibit typical UHI. The highs are only slightly higher in the city, but the lows are a few degrees colder in Kenosha. Does the table appear close to accurate to you, chicagogeorge? Is there something I am missing? I am currently working on precipitation and snowfall statistics.
I just spent some time looking into Northerly Island weather data on SERCC Nowdata, which only goes back to 2006. Interestingly, there was a drastic change in readings between 2012 and 2013 relative to other stations. Whereas prior to this Northerly Island's mean annual temperature was 1-2 degrees warmer than Midway, afterwards it has been 1-2 degrees cooler. This was not a gradual change, but rather a sudden one. I also compared it to O'Hare in case the changes occurred at Midway instead of Northerly Island, however, the results were the same when comparing Northerly Island with either Midway or O'Hare. After discovering this, I determined the difference between average maximum and minimum temperatures for each month when comparing the stations for the period since 2013. I then added/subtracted the differential to the 1981-2010 data at the station being compared to (Midway/O'Hare). The results were incredibly similar to those I predicted in the quoted post. Did some change occur at the Northerly Island weather station in 2012/2013? I believe the newer results to be more accurate, as they compare nicely with my other estimates. In addition, Northerly Island is slightly further north and located in a park, whereas Midway is in a dense neighborhood. Although Northerly Island is near downtown, the park setting means there should be less urban heat island than the location of Midway. One example of this concept is New York City, where Central Park is generally cooler than LaGuardia Airport. There is also a graph that illustrates the concept at the following website: https://www.google.com/amp/amp.usato...tory/14389371/. Therefore, I can find no explanation why Midway would have a lower annual mean temperature than Northerly Island. My results show that Midway's mean temperature is slightly cooler from November to March, but warmer during the rest of the year. This is especially apparent in late Spring and early Summer. Another interesting aspect of this climate's temperatures that I noticed is that it mirrors Boston closely from March through October. I will post the my exact estimates within a few days, although as I stated it is very similar to the last one I posted.
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