Glacier Sensitivity in the Monsoonal Himalayas: Relative Contributions of Feedback Mechanisms to Regional Glacier Mass Balance

Despite their societal relevance, glacier mass balances across High Mountain Asia (HMA) remain poorly constrained due, in part, to the limited number of direct measurements, regional climate heterogeneity, and uncertainty in glacier mass balance models. Many studies that model glaciers throughout HMA cite surface feedbacks as an important factor affecting glacier melt, however, little has been done to actually quantify their effects. This study develops a fully distributed surface energy- and mass-balance model to quantify the contributions of 3 surface feedbacks to glacier mass balance. The 3 target feedbacks are an accumulation/snow depth feedback, a sensible heat feedback, and an albedo feedback. The model follows well-known energy balance methods, but includes unique "switches" which allow individual feedbacks to be independently turned on and off. The model applies meteorological inputs from the High Asia Refined analysis to an idealized glacier for 4 different climate settings in HMA. The results show that surface feedbacks increase melt by up to 67% for a +1°C temperature forcing, but that feedback contributions vary significantly under different climate settings. For any given glacier, the feedback strength is highest near the equilibrium line altitude. Furthermore, feedbacks that directly reduce surface albedo consistently contribute the most to glacier mass loss. Feedback magnitude depends most strongly on the frequency of snowfall events occurring concurrently with the melt season, and on the magnitude of incoming shortwave radiation for that region. These results highlight the potential significance of feedbacks on glacier mass balance in HMA, what conditions maximize these feedback magnitudes, and what regions are likely most sensitive to them. They also highlight physical processes that need to be especially well constrained in future glacier mass balance models for glaciers in regions with high feedback sensitivity. Creating glacier mass balance models whose higher complexities focus on the processes that control regional glacier sensitivities to feedbacks for targeted glaciers will increase glacier mass balance constraints in HMA.