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Role of Fog in Urban Heat Island Modification in Kraków, Poland

Category: The interaction of fog with urban atmospheres and air pollution

Volume: 18 | Issue: 1 | Pages: 178-187
DOI: 10.4209/aaqr.2016.12.0581

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Anita Bokwa 1, Agnieszka Wypych1, Monika J. Hajto1,2

  • 1 Department of Climatology, Institute of Geography and Spatial Management, Jagiellonian University, 30-387 Kraków, Poland
  • 2 Institute of Meteorology and Water Management – National Research Institute, 30-215 Kraków, Poland


In cities located in concave landforms fog and UHI are strongly modified by the relief.
Fog formation decreases UHI in lowest city locations by 1 K at cloudless/windless weather.
Three types of spatial and temporal RMUHI pattern were found for days with fog.


The impact of fog on relief modified urban heat island (RMUHI) in Kraków has been presented using fog observations at 06 UTC from two meteorological stations: a rural one (Balice, B) and an urban one (Botanical Garden, BG) from the period 2006–2015. Daily UHI magnitude for the valley floor for the same period was estimated as TminBG–TminB, while for the period 2010–2015, eight daily courses of UHI were available, for the urban areas in the valley floor and 50 m above it, together with air temperature inversion data. UHI data for days with various combinations of fog occurrence and weather conditions were compared using non-parametric statistical tests: Wald-Wolfowitz test, Kolmogorov-Smirnov test and U Mann-Whitney test. Data of 2010–2015 were also the subject of cluster analysis (k-means method). Fog is an important factor decreasing UHI magnitude by about 1 K but mainly during weather conditions with little or no cloudiness and small wind speed or atmospheric calm, during anticyclonic synoptic situations, and only in the valley floor areas. With an increase in cloudiness and wind speed, the role of fog decreases and is similar in all parts of the city.


Fog Relief modified urban heat island Atmospheric circulation Cluster analysis

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