Effect of Temperature Adjustments on the Minneapolis-St. Paul Urban Heat Island

Abstract

In order to better estimate urban influence on local climate, mean temperature series were corrected for biases and heterogeneities. Annual, January and July mean temperatures for 21 stations in and around Minneapolis-St. Paul, Minnesota were adjusted for background climate, differences in observation time, and changes in station location. The effect of the adjustments on the spatial structure of the urban heat island was judged by comparing isopleth analyses of the adjusted and unadjusted temperatures for each of the three time periods. Adjusted temperature data depict a larger heat island that conforms more closely to the urban structure. The influence of the adjustments on the strength of the heat island was estimated by comparing urban-rural temperature differences calculated from both data sets for the three time periods. The mean urban minus mean rural temperature differences calculated from the adjusted data are as much as 5017o larger than the differences calculated from the unadjusted data.