Plowing paradise: snow clearing and urban solar radiation absorption

Abstract

Urban heat islands result from human modification of land surfaces. Snow cover reduces heating due to its reflectivity; however, urban snow is quickly plowed, thus altering surface radiative properties. The goal of this study was to evaluate the extent to which municipal snow removal affects the magnitude of solar input associated with changes in the radiation balance. Incoming and reflected shortwave radiation, surface radiating temperature, air temperature, and snow depth were measured with portable devices at eight sites in Syracuse, New York. Sites were classified as cleared, undisturbed, or snow piles. Measurements were taken following fresh snowfall, and continuing until snow had melted. A HOBO weather station provided hourly baseline conditions. Longevity of snow varied across snow site types, with greater persistence when in piles and on open areas. Albedo was reduced and surface temperatures were higher over cleared areas. The difference between absorbed energy due to clearing was quantified using an albedo regression model for undisturbed sites and comparing these to average reflectivity of cleared surfaces. The magnitude difference over the study period ranged from 841 million to 1670 million MJ. Snow plowing is therefore a significant source of additional energy that enhances the winter urban heat island.