Climate-Driven Glacier and Snowpack Changes in the Water Towers of Asia

Abstract:

The high mountain regions of Asia are a critical water resource within and downstream of those mountain systems, and is one of the most vulnerable water towers to climatic change. This is, in part, due to the water storage and supply role of the cryosphere within these mountain settings, and the sensitivity of cryospheric systems to even small changes in climate. Observations and models have advanced significantly in the past decade, providing unprecedented opportunity to assess magnitudes, rates, causes, and impacts of HMA cryospheric change. This has significantly advanced our knowledge of glacier mass changes over HMA. The results highlight rapidly accelerating glacier mass loss over the past 40+ years over the Himalayan range. While temperature change is generally accepted to play a role in this glacier loss, there is significant debate over the importance of other potential forcing mechanisms, such as changes in precipitation and light absorbing aerosols.

We utilize modern remote sensing imagery and a glacier mass balance model to assess the trends in snow covered area and aerosols for Himalayan glaciers over the past two decades, and the impact of those trends on glacier mass balance. The results show (1) aerosols have no discernable impact on glacier mass balance over this period, (2) trends in snow-covered area are important in the monsoonal Himalaya where surface albedo feedbacks are large, and (3) accelerating temperature changes in high mountain settings dominate glacier change. The regional importance of snow-covered area highlights the importance of precipitation phase, timing, and frequency on glacier response to climatic change. We reassess the geographical divisions between summer- and winter-dominated precipitation regimes in HMA using climate products of varying resolution. Our results demonstrate the spatial complexities in precipitation statistics in HMA when viewed through a topographic lens, and the resulting spatial complexity in glacier sensitivity to climate across the region. The results of this work highlight the recent trends in glaciers, snowpack, and aerosols in the Himalayas, temperature as the dominant driver of glacier change over this period, and the importance of precipitation in moderating glacier sensitivity to climate change now and in the future.