Changing spring air‐temperature gradients along large northern rivers: Implications for severity of river‐ice floods

Concern exists about future changes to air‐temperature gradients along large “northward”‐flowing Arctic rivers having the potential to affect the timing and severity of spring river‐ice breakup, and associated flooding events. To evaluate the significance of this concern, an analysis was conducted of temporal and spatial changes to the spring 0°C air‐temperature isotherm (I 0°C ), which is also known to be a good index for the timing of spring melt/breakup conditions. Changes in I 0°C were analyzed for the downstream 2000‐km main‐stem reaches of four large Arctic rivers: the Lena, Mackenzie, Ob and Yenisey. Current climatic conditions (1979–2008) were compared to those of two future climatic periods (2041–2070 and 2071–2100) projected by an ensemble of four Global Climate Models. Future projections show I 0°C chronology patterns along the rivers that closely parallel current conditions, but with earlier dates varying from an ensemble mean of 7.5 (13.6) to 16.5 (25.5) days for the 2050s (2080s). Results also reveal a progressive downstream increase in warming under future climates. At the time when headwater temperatures reach 0°C, river mouth to headwater temperature differences for the four rivers decrease by an average of 0.8°C (2.4°C) to 2.1°C (3.7°C) for the 2050s (2080s). The implications of such decreases on the severity of spring ice‐jam floods are discussed.