Interior Alaska River Ice Breakup and Climate

The link between Interior Alaska river (Yukon, Tanana, and Kuskokwim Rivers) ice breakup date and the large-scale winter climate is investigated to assess seasonal predictability. Multiple rivers in Interior Alaska are examined. The climate-river relationship is examined using standard climate analysis techniques of correlation, regression, composite and time series. The mechanisms that control the timing of breakup depend both on local and regional temperature and precipitation, so the analysis is carried out at hemispheric, regional, and local scales. During the warm (cold) phase of ENSO fewer (more) storms travel into the Gulf Alaska during the spring, resulting in a decrease (increase) of cloud cover and consequently increased (decreased) solar insolation reaching the surface. This results in warmer (cooler) than average surface air temperatures in spring (April-May) and an earlier (later) breakup date. Our results indicate that breakup is most strongly controlled locally by surface air temperature in spring. Additionally, low frequency variability is evident in the smoothed breakup time series, and is consistent with a previously identified regime shift in the Pacific in 1989. Our findings show that the variability of breakup in Alaska is linked to the large-scale climate through storm track processes in the Pacific; this gives insight into the predictability of breakup.