Reply on RC1

Stefan Fugger

doi:10.5194/tc-2021-97-ac1

Abstract

The Indian and East Asian Summer Monsoons shape the melt and accumulation patterns of glaciers in High Mountain Asia in complex ways due to the interaction of persistent cloud cover, large temperature amplitudes, high atmospheric water content and high precipitation rates. While the monsoons dominate the climate of the southern and eastern regions, they progressively lose strength westward towards the Karakoram, where the influence of Westerlies is predominant. Despite the major role of the monsoon in the Himalayas, a holistic understanding of their influence on the region's glaciers is lacking because previous applications of energy- and mass-balance models have been limited to single study sites. In this study, we use a full energy- and mass-balance model and seven on-glacier automatic weather station datasets from different parts of the Himalayas to investigate how monsoon conditions influence the glacier surface energy and mass balance. In particular, we look at how debris-covered and debris-free glaciers respond differently to monsoonal conditions. The radiation budget mostly controls the melt of clean-ice glaciers, but turbulent fluxes also play an important role in modulating the melt energy on debris-covered glaciers. The sensible heat flux reduces during core monsoon, but the latent heat flux removes energy from the surface due to evaporation of liquid water. This interplay of radiative and turbulent fluxes, together with compensations between increasing and decreasing melt rates over the diurnal cycle, causes debris-covered glacier melt rates to stay almost constant over the entire ablation period through the different phases of the monsoon. Ice melt under thin debris, on the other hand, is amplified by both the dark surface albedo and the turbulent fluxes, which act as a source of energy through surface heating and condensation, especially during monsoon. Pre-monsoon snow cover can considerably delay melt onset and have a strong impact on the seasonal mass balance. Intermittent monsoon snow cover further modulates the melt rates at high elevation. Given our results, we expect the mass balance of debris-covered glaciers to react less sensitively to projected future monsoon conditions than clean-ice and dirty-ice glaciers. This work is fundamental to the understanding of the present and future Himalayan cryosphere and water budget evolution, while informing and motivating further glacier- and catchment-scale research using process-based models (Yang et al., 2017).

Highlights

High Mountain Asia (HMA) holds the largest ice volume outside the polar regions (Farinotti et al, 2019) and due to the large elevation range and vast geographic extent, HMA glaciers are highly diverse in character and hydro-climatic situation (Yao 25 et al, 2012)
The Indian Summer Monsoon dominates the Central Himalaya and the Southeastern Tibetan Plateau during summer, and gradually loses strength moving towards the Karakoram, Pamir and Kunlun ranges in the east, where the influence of Westerlies is strong
It is an important control of both amounts and patterns of ice melt, as ice melt rates are suppressed during periods of snow cover (Figure 5)

Summary

Introduction

High Mountain Asia (HMA) holds the largest ice volume outside the polar regions (Farinotti et al, 2019) and due to the large elevation range and vast geographic extent, HMA glaciers are highly diverse in character and hydro-climatic situation (Yao 25 et al, 2012). A more continental, monsoon-westerlies-influenced regime controls the Central Tibetan 30 Plateau (Yao et al, 2012; Mölg et al, 2014), and the East Asia Monsoon influences the eastern slopes of the Tibetan Plateau (Maussion et al, 2014; Yao et al, 2012) These major modes of atmospheric circulation do control the surface processes and runoff regimes of glaciers (e.g. Mölg et al, 2014, 2012; Kaser et al, 2010) and lead to distinct responses of glaciers to climate change (Yao et al, 2012; Sakai and Fujita, 2017; Scherler et al, 2011b; Kraaijenbrink et al, 2017). Mass losses are high throughout most of HMA, and are pronounced on the South-Eastern Tibetan Plateau, 35 while glaciers exhibit a near-balance regime in the Karakoram, Pamir and Kun Lun (Farinotti et al, 2020; Gardelle et al, 2012; Brun et al, 2017; Shean et al, 2020)

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