Influence of aerosol radiative effects on temperature and snow cover fraction in the Himalayan region: GCM simulations

Abstract:

Recent increases in temperature and acceleration of snowmelt have had an enormous impact on the sensitive ecological system of the Hindu Kush Himalayan (HKH) region. To investigate possible links to changes in levels of coincident aerosols, simulations were made with atmospheric general circulation model, ECHAM6-HAM2, from 1971-2010. Evolving forcing agents were prescribed, including sea surface temperature (SST) and sea ice concentration (SIC) from the Atmospheric Model Intercomparison Project (AMIP) and AEROCOM emission inventory (Dentener et al., 2006), represents a present day scenario. The simulated surface temperature showed an increasing trend in the range of 0.1-0.7 ^OC/decade with the highest in western and central region of HKH. Simultaneously, simulated snow cover fraction (SCF) showed a decreasing trend throughout the Himalayan belt. Increases in absorbing aerosols, including black carbon and dust, in the surface layer were seen to cause an increase in the shortwave heating rate (SHR), reaching up to 0.15 K/day-decade, which bore a positive correlation (0.7) with surface temperature. Further, a negative correlation between surface temperature and SCF was found. The model version does not parameterize surface temperature changes from snow albedo changes with absorbing aerosol deposition. Using an empirical formula (Ming et al., 2009), the estimated black carbon concentration in the snow was found to be 150-350 ug/kg, with a consequently significant snow albedo change. Significant differences were found in among HKH regions in warming and snowmelt rates, which correlate with aerosol abundances and radiative effects. The magnitude of effects simulated here would increase in model versions where snow albedo feedback to surface temperature is taken into consideration.