Heating and cooling in Colorado mining towns

The urban climate literature is replete with analyses of growing communities and cities and their effect on the temperature record. Very little research has considered the declining town and its effects on climate. Our fieldwork in Silverton, Colorado, peaked our interest on whether declining anthropogenic activity within a town and the accompanying land use changes would have induced noticeable effects on the 20th century temperature record. Such effects, we hypothesize, should produce a cooling trend. This paper primarily focuses on the town of Silverton, because the authors have experience in snow/ice research in this location since 1976. As part of those endeavors, students from respective institutions have been trained in snow/ice processes, variations of climate with elevation, and avalanche risks, in addition to human features of the town's activities during the 20th century. However, to learn of the general phenomena of cooling and/or warming in mountain towns in the region, we have chosen other climate stations of Telluride, Durango and Hermit, Colorado, all GHCN sites. Twentieth century population data were accessed for all these places, detailed sub-station histories were obtained from the Colorado Climate Center, and mapping and visits to all station locations were accomplished. All of these points are crucial to interpreting the trends that were revealed. The analysis of temperature and population trends, focused on decadal time scales, reveals the existence of a diminished town heat island effect during the past century. This effect is a cooling, especially notable in the average January minimum temperatures, and appears to be the result of a combination of both diminished anthropogenic activities caused by the boom and bust cycles of mining during the 1900s and station location changes. Results also indicate that Telluride and Silverton have a substantial cooling trend relative to the Hermit weather station, which is a rural ranch location at similar altitude and terrain setting. Conversely, Durango experienced population growth and demonstrates the classic town warming through time. In sum, the small towns analyzed have quite sizeable warming and cooling effects most likely due to major temporal changes of anthropogenic activity and land surface conditions nested within the surrounding snow and terrain landscape of these mountainous sites.