Comment on tc-2022-256

Abstract

Earth System Models (ESMs) can help to improve the understanding of climate-induced cryospheric-hydrological impacts in complex mountain regions, such as High Mountain Asia (HMA). Coarse ESM grids, however, have difficulties in representing cryospheric-hydrological processes that vary over short distances in complex mountainous environments. Variable-resolution (VR) ESMs could help to overcome these limitations. This study investigates the ability of the VR-Community Earth System Model (VR-CESM) to simulate cryospheric-hydrological variables such as glacier surface mass balance (SMB) over HMA. To this end, a new VR grid is generated with regional grid refinement up to 7 km over HMA. Two coupled atmosphere-land simulations are run for the period 1979–1998. The second simulation is performed with an updated glacier-cover dataset and includes snow and glacier model modifications. To evaluate the outcomes, comparisons are made to gridded outputs derived from a globally uniform 1degree CESM grid, observation-, reanalysis-, and satellite-based datasets, and a glacier model forced by a regional climate model (RCM). In general, climatological biases are reduced compared to the coarse-resolution CESM grid, but glacier SMB is too negative relative to observation-based glaciological and geodetic mass balances as well as RCM-forced glacier model output. In the second simulation, the SMB is improved but still underestimated due to cloud-cover and temperature biases, missing model physics, and incomplete land-atmosphere coupling. The outcomes suggest that VR-CESM could be a useful tool to simulate cryospheric-hydrological variables and to study climate change in mountainous environments, but further developments are needed to better simulate the SMB of mountain glaciers.