Merging operational satellite and historical station snow cover data to monitor climate change

Abstract

Since the middle of 1987, snow cover Northern Hemisphere lands has been less extensive than at any time since the advent of reliable satellite snow charting in 1972. In fact, 1990 should of down as being the lowest snow year on record: monthly minima have been established for February through September (based on observations through September). However, with less than a two-decade long record of satellite observations of snow cover, it is impossible to place this recent dearth of cover in proper perspective. To do so requires a longer period of record, one which can only be supplied from station data. Regional intercomparisons of visible satellite-derived snow products and networks of station observations agree well on a seasonal time scale, given a network of high-quality stations in non-mountainous terrain. Thus, where these conditions are met, lengthy time series of regional snow cover may be compiled confidently from station observations, permitting documentation of natural fluctuations and trends of cover that may occurred over the past century. For instance, decadal fluctuations in snow cover have been identified over the United States Great Plains this century, and a trend towards increasing duration of cover from the 1930's to 1970's has been observed in the central Plains. Such information enhances the utility of satellite-derived snow cover observations identifying and monitoring future climate change.