Spatial and temporal variations in annual balance of North Cascade glaciers, Washington 1984–2000

Abstract Since 1984, annual glacier mass balance measurements have been conducted on eight glaciers by the North Cascades Glacier Climate Project (NCGCP). Since 1993 the National Park Service (NPS) has monitored the mass balance of four glaciers, and the NCGCP an additional two glaciers. This 14 glacier monitoring network, covering an area of 14 000 km 2 , represents the most extensive network of mass balance measurements for alpine glaciated areas in the world. The breadth of the record allows determination of the annual variability of annual balance from glacier to glacier, and from year to year. Data indicate a broad regional continuity in the response of these glaciers to climate. All cross‐correlation values between any pair of the 14 glaciers ranged from 0·80 to 0·98. This strong degree of correlation indicates that regional‐scale climate conditions, not local microclimates, are the primary control of glacier annual balance in the North Cascades. Data also indicate that the annual mass balance trend for glaciers was strongly negative from 1984 to 1994 and slightly positive from 1995 to 2000. The cumulative annual mass balance for eight glaciers between 1984 and 1994 was −0·39 m year −1 . From 1995 to 2000 the cumulative annual mass balance of the same eight glaciers was +0·10 m year −1 , and +0·15 m year −1 for all 14 glaciers in this study. The correlation coefficients indicate the strongly similar response, not that the specific magnitude of the annual mass balance for each glacier is the same. There is a significant annual range in the individual glacier balances, averaging 1·01 m, and in the mean annual mass balance between glaciers. All of the glaciers with more positive annual mass balances since 1995 had either significant accumulation areas extending above 2300 m, and/or are east of the zone of maximum precipitation. The glaciers with the most negative annual mass balance are those with the lowest mean elevation. The record is, as yet, too short to explain the variability of mass balance fully using climate data and seasonal mass balance data. Copyright © 2001 John Wiley & Sons, Ltd.