Climate data continuity in urban areas has long been plagued by problems of instrument exposure, station moves, and changes in the environment surrounding existing monitoring sites. Consistent long-term monitoring has rarely been the focus of data collection activities. For example, since the 1930s and 40s, the emphasis in data collection in urban areas has been to support the interests of aviation with a lower priority given for climatic concerns.
In terms of long-term climate data continuity, Denver, Colorado has fared better than many cities in the United States. While the homogeneity of climate records are far from ideal, there have been relatively few station moves since early in the 20th Century, significant station overlap when moves have occurred, and nearby stable cooperative observing sites for reference. However, a combination of recent changes have compromised Denver’s climate data continuity. The completion of Denver International Airport in early 1995, the introduction of ASOS (Automated Surface Observing System), and the planned relocation of the National Weather Service Forecast Office from Denver to Boulder in early 1999 are all affecting climate data continuity.
This paper will examine the affects of recent observing changes on climate data continuity. Temperature will be the focus of this study, but precipitation and other elements will be examined briefly. Three years of data from ASOS at the new Denver International Airport will be compared to observations from eight cooperative weather observing sites in and around the Denver metropolitan area. Station to station differences will be explored as a function of time of year and also as a function of weather condition (clear, cloudy, calm, windy, etc). Regional temperature patterns derived from surface observations will be developed. Data discontinuities associated with known changes in station locations and instrumentation will be pointed out. Finally, an example single long-term temperature time series will be constructed for downtown Denver and compared to data from a recently installed cooperative station in the downtown area.