Changing Station Coverage in the Upper Colorado River Basin: Is This a Problem?

Abstract:

Almost 40 million people living in the arid western U.S. depend on the Colorado River. The high demand, recent drought, and paleoclimatic studies documenting long, severe droughts have spurred numerous studies on the drivers of Colorado River flow. Understanding low-frequency variability and trends in a large and complex basin like the Upper Colorado (UCRB), which contributes the vast majority of Colorado River flow, requires long, high-spatial resolution climatological records. However, researchers sometimes find discrepancies between long climate data products and hydrological records. One explanation for such disparities is the composition of the climate data record. The National Center for Environmental Information’s Master Station History Report (MSHR) documents significant changes in the number and spatial distribution of weather stations within the UCRB. These shifts are reflected in the basin-average station elevation, which has varied by over 300m since 1950 and by over 365m since 1875. Strong elevation and aspect controls on both temperature and precipitation combined with the high degree of variability in station location could drive trends in gridded products in the absence of real climatological trends, although differences in base data, spatial resolution and gridding algorithms can complicate comparisons. Yet limiting analysis to only those stations with long, consistent records is impractical and would be problematic as station density in the early part of the record was not sufficient to characterize the basin. Here we document changes in station coverage within the UCRB and identify the degree to which coverage may have influenced climatic trends.