WRAL WeatherCenter Blog

When giving the record lows and highs and denoting whether we've broken either, is the amount of growth taken into consideration? It seems that the more a town grows ( concrete, brick, asphalt etc.) the warmer it becomes over the decades. I've noticed this over the many years of watching your reports. So if we're setting a record high this season is it really hotter than it was 30 or so years ago in comparison?

Posted June 17, 2008

MIKE MOSS SAYS:        Linda,       The short answer to that question is no, there isn't any particular adjustment or accounting in records that are reported on air for such "urbanization" effects. Over time, as you note, some reporting locations that become increasingly urbanized develop a "heat island" effect that can push average temperatures (and associated records) upward on a localized basis. There certainly could be some component of such an effect at the RDU airport, although it should be somewhat muted by the airport's location on the northwest side of Raleigh and the southeast side of Durham. We have a prevailing southwest flow in the area that places the airport frequently downstream from a part of the region that is relatively suburban to rural and still notably wooded. Another consideration in terms of new record temperatures (be they record highs or record lows) is the fact that the period of observation has a finite starting point. In that since, it was only 64 years ago that every day at the airport set a new RDU record! The longer you maintain observations that start from a fixed point in time, the larger the span of possible conditions you sample, and therefore the larger the likely range between the hottest and coldest readings for a given day or month. For that reason, even if there were no larger scale trends in temperature (either due to weather pattern chages or to localized land use variations) you would continue to see occasional excursions to new record values, at a rate that would gradually approach zero as the length of the time series approached infinity. Of course, if you superimposed a long-term warming trend on that series, record highs would become more numerous than record lows, and vice versa for a cooling trend.


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