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We present a number of time-lapse images and satellite observations of regional climate change over mountain-snow areas in terms of snow albedo reductions for decadal and seasonal timescales. For seasonal variation critically important for hydrology and water resources, we illustrate from the 12-year MODIS satellite dataset analysis that the snow albedo reduction from March to April is caused in part by the deposition of absorbing aerosols associated with an increase in aerosol optical depth over the Sierra Nevada in the Western United States and the Southern Tibetan Plateau. In addition to global warming, the reduction of mountain snow cover must be related to interactions of 3D topography and incoming solar radiation as well as the deposition of black carbon (BC), and dust particles.We then describe the 3D solar radiative transfer over inhomogeneous and complex topography by means of Monte Carlo photon tracing calculations and its correlation parameterization using a number of key parameters defined by the position vector with reference to the sun over a mountain slope in terms of direct and diffuse fluxes, including mountain to mountain interactions. This is followed by a brief discussion of parameterization of the spectral light absorption and scattering by BC/snow system in terms of the extinction coefficient, single-scattering albedo, and asymmetry factor for snow grains contaminated by BCs during their aging processes in the atmosphere. For multiple BC internal mixing, we have innovated a stochastic process to place coated BCs of various sizes within the 3D snow grain domain using BC mass as input in view of the fact that physical equations to define internal mixing do not exist.The effects of 3D radiative transfer and snow albedo reduction induced by internal BC absorption are illustrated by a number of model simulations. The first involves the use of GEOS-Chem with a resolution of ~ 200 km for the study of the impact of BC deposition on snow reduction and radiative forcing analysis. In the second, we employed CCSM4, a global model with a resolution of 0.9o x 1.25o for a 10-year climate run to investigate the 3D radiative transfer impact on cloud, snowmelt, runoff, temperature, and circulation patterns over the Tibetan Plateau in winter and summer. In the third, we modified WRF-Chem to include both BC deposition and 3D topography to study their impacts on precipitation over mountain regions in the Western United States using a Pineapple Express case. A number of pertinent results are presented and physically discussed. Finally, we present a preliminary unification of the evolution of BC in the atmosphere produced by anthropogenic emission and its dry and wet depositions onto snow grains over the Tibetan Plateau, using the widely-known Noah-MP land surface model as a prototype to study the impact of BC on snow albedo reduction and feedback.

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