Micro-Meteorological Impact of Glacier Retreat and Proglacial Lake Temperature in Western Norway

Glaciers are retreating worldwide, yet, little is known about the influence of these changes on local weather and climate in glacial landscapes. Changes in glacier extent and proglacial lakes alter the thermodynamic forcing in glacier-lake-valley systems that may be of similar or greater importance for future microclimate than direct effects of global warming. To study the impact of these changes, we combine the first set of high-density spatiotemporal observations of a glacier-lake-valley system at Nigardsbreen in western Norway with high-resolution numerical simulations from the Weather Research and Forecasting (WRF) model. The sensitivity of the thermodynamic circulation to glacier extent and proglacial lakes is tested using glacier outlines from 2006 and 2019 as well as varying lake surface temperature. The model represents the evolution of glacier flow and cold air pools well when thermal forcing dominates over large-scale forcing. During a persistent down-glacier flow regime, the glacier-valley circulation is sensitive to lake temperature and glacier extent, with strong impacts on wind speed, convection in the valley, and interaction with mountain waves. However, when the large-scale forcing dominates and the down-glacier flow is weak and shallower, impacts on atmospheric circulation are smaller, especially those related to lake temperature. This high sensitivity to meteorological conditions is related to whether the flow regime promotes thermal coupling between the glacier and the lake. The findings of this study highlight the need for accurate representation of glacier extent and proglacial lakes when evaluating local effects of past and future climate change in glacierized regions.