Reconciling precipitation trends in Alaska

Numerous studies have evaluated precipitation trends in Alaska and come to different conclusions. These studies differ in analysis period and methodology and do not address the issue of temporal homogeneity. To reconcile these conflicting results, we selected 29 stations with largely complete monthly records, screened them for homogeneity, and then evaluated trend over two analysis periods (1950–2010 and 1980–2010) using three methods: least absolute deviation regression, ordinary least squares regression (with and without transformation), and Mann-Kendall trend testing following removal of first-order autocorrelation. We found that differences in analytical period had a significant impact on trends and that the presence of inhomogeneities or step changes also posed a substantial challenge in detecting reliable long-term trends in precipitation over Alaska, particularly in the southern part of the state. Although some of these inhomogeneities occur in the mid-1970s and could be associated with well-documented changes in the Pacific Ocean and the Aleutian Low at that time, many of the inhomogeneities co-occur with changes in station location, instrumentation, or operation. These operationally induced changes make it difficult to accurately detect the impact of decadal to multidecadal climate variability on precipitation amounts and to assess historical precipitation trends in Alaska.
McAfee, S.A., G. Guentchev, and J.K. Eischeid
Journal of Geophysical Research