Warming-induced monsoon precipitation phase change intensifies glacier mass loss in the southeastern Tibetan Plateau

Abstract

Glaciers are key components of the mountain water towers of Asia and are vital for downstream domestic, agricultural, and industrial uses. The glacier mass loss rate over the southeastern Tibetan Plateau is among the highest in Asia and has accelerated in recent decades. This acceleration has been attributed to increased warming, but the mechanisms behind these glaciers’ high sensitivity to warming remain unclear, while the influence of changes in precipitation over the past decades is poorly quantified. Here, we reconstruct glacier mass changes and catchment runoff since 1975 at a benchmark glacier, Parlung No. 4, to shed light on the drivers of recent mass losses for the monsoonal, spring-accumulation glaciers of the Tibetan Plateau. Our modeling demonstrates how a temperature increase (mean of 0.39 ∘ C ⋅dec −1 since 1990) has accelerated mass loss rates by altering both the ablation and accumulation regimes in a complex manner. The majority of the post-2000 mass loss occurred during the monsoon months, caused by simultaneous decreases in the solid precipitation ratio (from 0.70 to 0.56) and precipitation amount (–10%), leading to reduced monsoon accumulation (–26%). Higher solid precipitation in spring (+18%) during the last two decades was increasingly important in mitigating glacier mass loss by providing mass to the glacier and protecting it from melting in the early monsoon. With bare ice exposed to warmer temperatures for longer periods, icemelt and catchment discharge have unsustainably intensified since the start of the 21st century, raising concerns for long-term water supply and hazard occurrence in the region.

Multi-decadal monsoon characteristics and glacier response in High Mountain Asia

“…Parlung Glacier Number 4 (29.245 • N 96.928 • E, hereafter 'Parlung 4' or 'PAR4') is a 11.7 km 2 , spring-type accumulation glacier in the southeastern Tibetan Plateau. The glacier has been the focus of several recent studies that have explored meteorological processes (Yang et al 2011, Shaw et al 2021, glacier dynamics (Yang et al 2020) and energy/mass balance (Zhu et al 2015, 2018, Jouberton et al 2022. Mugagangqiong Glacier (34.248 • N 87.490 • E, hereafter 'MUGA' for tables and figures) is a 2 km 2 glacier in the arid central Tibetan Plateau.…”

“…(Steiner et al 2021) were used to generate hourly-monthly temperature lapse rates, and temperatures were adjusted for the boundary layer cooling effect of Yala using the onglacier AWS temperatures. For Parlung 4, we consider the off-glacier temperature lapse rates derived from the data of Shaw et al (2021) and as applied by Jouberton et al (2022). Precipitation is distributed similarly to Jouberton et al (2022) who applied a correction factor of 1.75 and gradient of 14% 100 m −1 to account for the distinct precipitation regime between valley and the glacier.…”

“…For Parlung 4, we consider the off-glacier temperature lapse rates derived from the data of Shaw et al (2021) and as applied by Jouberton et al (2022). Precipitation is distributed similarly to Jouberton et al (2022) who applied a correction factor of 1.75 and gradient of 14% 100 m −1 to account for the distinct precipitation regime between valley and the glacier. Given the differences in model forcing and structure, we recalibrate these gradients for the current study against ablation stakes and an upper elevation ice core record (table S3).…”

“…For example, the suggested weakening of the South Asian Summer Monsoon since the 1950s, exacerbated by anthropogenic aerosol emissions, has resulted in observed summertime drying across much of northern India and towards the Nepalese Himalaya (Bollasina et al 2011). Conversely, a tendency towards earlier monsoon onset over the Bay of Bengal can be linked to increases in May precipitation in the southeastern Tibetan Plateau (Zhu et al 2020, Jouberton et al 2022, accelerating wetting and greening in recent decades (Zhang et al 2017). While the full mechanisms remain elusive (e.g.…”

“…While the full mechanisms remain elusive (e.g. Saha and Ghosh 2019), the complex interaction of temperature and precipitation changes have important implications for both glacier accumulation and ablation, largely through precipitation phase and albedo (Jouberton et al 2022). While it has been established that the dynamics of the summer monsoon, as well as longterm climatic trends, local geography (Yao et de Kok et al 2020) and even land use change ( de Kok et al 2018) all contribute to the heterogeneity of glacier mass balance in HMA, responses of glaciers' mass balances in different sub-regions to multidecadal variability in the monsoon remains largely unexplored (Arndt et al 2021).…”