PARENT SESSION
Oral Session #33: Climate Change. Presiding: A. Peterson.
Tuesday, August 7, 2001. 1:00 PM to 5:00 PM. Hall of Ideas E.
Variability and extreme events in long-term lake and river ice phenology across the northern hemisphere.
BENSON, BARBARA1, KRATZ, TIMOTHY1, MAGNUSON, JOHN1, 1
ABSTRACT- Lake and river ice phenology provide long-term climate indicators across the northern hemisphere. Our previous publications demonstrated a trend toward later freeze and earlier thaw dates over the 150-year period from 1846-1995 and an increase in variability in freeze and thaw dates and ice duration in the period 1971-1990 as compared with 1951-1970. Here we ask whether the trend in increasing variability exists over the 150-year period and whether a pattern exists in the occurrence of extreme events. Data come from the Lake Ice Analysis Group Database. We removed the linear trend and computed the standard deviations of freeze and thaw data for five-year windows. For the eleven water bodies with at least 140 years of thaw data, eight showed a decreasing trend in standard deviation over the 150-year period and an increasing trend over the period since 1950. For the six water bodies with a continuous record from 1846-1995, 72 percent of the 50-year events for late thaw occurred from 1846-1895 whereas only 6 percent of these extreme events occurred from 1946-1995. In contrast, only 6 percent of the 50-year events for early thaw occurred from 1846-1895 whereas 50 percent occurred from 1946-1995. These preliminary analyses suggest that more extreme cold events occurred earlier in the record and that some lakes exhibited decreased variability in ice thaw dates over the past 150 years and increased variability since 1950.
KEY WORDS: ice phenology, climate change, extreme events