A Hierarchical Modeling Approach for the Himalaya-Karakoram Glaciers

The complex glaciological environments of the Himalaya-Karakoram-Hindukush (HKH) mountains require comprehensive process-based assessments to understand the current state and future evolution of glaciers. To advance our understanding of the dominant processes driving glacial change in this region, we conduct a hierarchical modeling assessment of a glacier subset in the Eastern Himalayas and the Karakoram. Simple ice flow models require limited data and may be suitable for the data sparse HKH region, however, they cannot capture detailed processes (e.g., higher order ice dynamics) that may be important for steep and narrow valley glaciers. We therefore employ a three-step hierarchical modeling approach to gain insight into glacier behavior, i.e., starting from simpler models and gradually moving to more advanced modeling systems while developing an understanding of the governing processes step-by-step. We first assess changes in glacier length in response to atmospheric forcing using a linear geometric model that solves a third-order linear differential equation for the glacier length. The second stage employs a more sophisticated analysis of the glacier geometry and dynamics using the Open Global Glacier Model. Finally, we use the Community Ice Sheet model to simulate higher order dynamics of these glaciers. We discuss the modalities of the three models and the types of science questions they are best suited to address.