Changing station coverage impacts temperature trends in the Upper Colorado River basin. (13th November 2018)

• Record Type: Journal Article
• Authors: McAfee, Stephanie A.; McCabe, Gregory J.; Gray, Stephen T.; Pederson, Gregory T.
• Is Part Of: International journal of climatology. Volume 39:Number 3(2019)
• Page Start: 1517
• Page End: 1538
• Publication Date: 2018-11-13
• Subjects: climate trends -- Colorado River -- elevation‐dependent warming -- gridded data -- temperature; Climatology -- Periodicals; Climat -- Périodiques; Climatologie -- Périodiques; 551.605
• DOI: 10.1002/joc.5898
• Languages: English
• ISSNs: 0899-8418

Abstract

Abstract : Over the Upper Colorado River basin (UCRB), temperatures in widely used gridded data products do not warm as much as mean temperatures from a stable set of U.S. Historical Climatology Network (USHCN) stations, located at generally lower elevations, in most months of the year. This is contrary to expectations of elevation‐dependent warming, which suggests that warming increases with elevation. These findings could reflect (a) a genuine absence of elevation‐dependent warming in the region, (b) systematic non‐climatic influences on either the USHCN stations or high‐elevation stations, including known inhomogeneities related to changes in the time of observation and instrumentation, or (c) suppression of an elevation‐dependent warming signal introduced by changes in the station network. While we cannot categorically dismiss the first two possibilities, we show here that over portions of the 20th century, gridded temperatures warm less than USHCN temperatures, and the difference cannot be explained by accounting for known inhomogeneities. These analyses suggest that changing station coverage in the UCRB has influenced trends in gridded temperature estimates that incorporate changing suites of stations over time. Specifically, increases in the number of high‐elevation stations in the UCRB may have led to an underestimation of elevation‐dependent warming, particularly during the spring. This phenomenon is unlikely limited to this specific basin and may be present in other high‐elevation watersheds across the western United States Abstract : The effects of systematically changing station coverage are profound and significantly impact our ability to assess long‐term trends where instrumentation is sparse. Data sets disagree in ways that are consistent with choices made during product development, so that it is critical for users to understand and acknowledge each data set's specific characteristics, in much the same way that the community already addresses differences between the many hydrological models that are in use. Annual average differences between PRISM and U.S. Historical Climatology Network minimum (blue) and maximum (red) temperature estimates that have (solid) and have not (dashed) been adjusted for inhomogeneities across the UCRB relative to the average elevation of the available station network (purple). Cyan shading shows the period of time when the record might be influenced by the inclusion of data from SNOTEL sites. Marking the onset of potential inhomogeneities related to SNOTEL instrumentation.