LAUSR

This study examines the climatic drivers of ice-off dates for lakes and rivers across the Northern Hemisphere. Most lakes and rivers have trended toward earlier ice-off dates over the last century, as would be expected from long-term climate change. However, we also identify modes of climate variability that significantly impact the short-term behavior of ice-off time series. In particular, the North Atlantic Oscillation (NAO), Pacific-North American Pattern (PNA), and to a lesser degree the El Niño-Southern Oscillation (ENSO) explain a substantial fraction of the interannual variance in melt dates, while the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) generally do not. Furthermore, the spatial pattern of the early or late ice-off dates associated with the NAO, PNA, and ENSO matches a priori expectations due to the known surface temperature patterns associated with these oscillations. In all regions, the strongest correlation to ice-off is with one of the high-frequency modes—the NAO or PNA, suggesting that short-term weather variations play a stronger role than lower-frequency climate variability (ENSO, PDO, AMO) in driving ice-off.