ALBERT

Description: The cryosphere is a crucial water storage and buffer in the Amu Darya River basin, which receives little precipitation downstream of the Pamir and Hindu Kush mountains. Lowland agriculture and livelihoods heavily rely on the water released from the cryosphere, especially during the summer period. While the Pamir glaciers exhibited near-neutral mass balance in recent decades, the future of the region’s mountain water supply depends on how snow and glaciers will respond to continued climate change.We apply a state-of-the-art land surface model to the Kyzylsu catchment, a recently established research catchment in the basin’s glacierized headwaters, for the recent past and for four decades into the future. We force the model with an ensemble of CMIP6 SSP scenarios downscaled to 100m spatial resolution. The model is constrained and evaluated with in-situ observations and remote sensing data. We study the present and future of the catchment’s water and ice mass balances and in particular the energy driven partitioning of fluxes into runoff and vapor. We investigate whether the catchment’s cryosphere is at a tipping point towards a negative mass balance, as it has been hypothesized for the wider region, as well as whether peak water will be reached by the middle of the 21st century. This study provides an important insight into the efficacy of mechanistic models to reveal the hydrological functioning of the region’s headwater catchments and to project their future evolution.

Description: High Mountain Asia (HMA) hosts the largest mass of ice outside the Polar Regions and provides water to large downstream communities. Glacier change has been highly diverse across the region over the last decades, with glaciers in the Pamirs experiencing near-neutral mass balance while fast rates of mass loss are observed in the Southeastern Tibetan Plateau (STP). In a previous modelling study in the STP, we found that precipitation phase changes associated with climate warming were a major accelerator of glacier losses, but this mechanism of mass loss acceleration has yet to be explored across the rest of HMA. High-elevation measurements of precipitation phase are rare, especially along glacierized elevations, which lie at the solid-mixed-liquid boundary during summer months. Therefore, accurate representation of precipitation phase in models is essential for quantifying glacier accumulation rates and projecting change.Here we use downscaled and bias-corrected ERA5-Land reanalysis to show the high sensitivity of the solid precipitation ratio to the choice of parameterisation and its impacts on the seasonality of simulated snowfall accumulation at three glacierized catchments covering distinctive climates in HMA (Kyzylsu in the Northern Pamirs, Trakarding-Trambau in the Nepalese Himalayas and Parlung No.4 in the STP). We then apply a land-surface model at high spatio-temporal resolution (100m, hourly) to show the effect of the precipitation phase parametrization on the simulated glacier-mass balance, snowpack dynamics and catchment hydrology. Our results highlight the need to better constrain precipitation phase in glaciological studies and to consider the uncertainty associated with the choice of parameterisation.

Description: Glaciers in the European Alps recorded exceptional melt volumes in the summer of 2022. Impressions from High Mountain Asia also suggested higher-than-usual mass loss. Our observations at seven hotspots in the Pamir mountains highlighted glaciers suffering from small accumulation areas at the end of the balance year, due to reduced winter snowfall and increased summer melt. The glacier mass budget of this mountain range has been regarded as part of the Pamir-Karakoram Anomaly, but the most recent satellite observations suggest that the Karakoram Anomaly is coming to an end. Here, we draw together field and remote sensing observations to assess the severity of Pamir mass loss in recent years, and in the extreme 2022 summer in particular, as compared to the historical baseline. We examine climatic records and reanalyses to establish the degree to which recent years fit within the observed historic seasonal and annual ranges. We compare the recent to historic mass balance measurements at Abramov Glacier, the single long-term monitoring reference glacier for the region. We combine geodetic glacier mass balances surveyed from a variety of sources to consider how well observations agree with one another. We then consider changes to observed glacier surface albedo and surface temperature over the past 20 years based on satellite record. Finally, we examine interannual and decadal changes to on-glacier and catchment snowlines. Taken together, these data sources enable us to link direct meteorological and glaciological conditions to broad spatial and temporal patterns of change across the Pamir mountains.