Climatic trends in major U.S. urban areas, 1950-2009

Abstract

We evaluate changes in climatic indices for the 100 largest U.S. urban areas and paired surrounding non-urban areas. During the period 1950-2009, we find that there were statistically significant changes in as many as half of the urban areas in temperature-related indices, such as heating and cooling degree-days and number of warm and cool nights, almost all of which are reflective of a general warming. Similarly, statistically significant changes (mostly increases) in indices related to extreme precipitation, such as daily maximum intensities and number of days with heavy precipitation, were detected in as many of 30% of the urban areas. A paired analysis of urban and surrounding non-urban areas suggests that most temperature-related trends are attributable to regional climate change, rather than to local effects of urbanization, although the picture is more mixed for precipitation. Copyright 2011 by the American Geophysical Union.