Integrated simulation of snow and glacier melt in water and energy balance‐based, distributed hydrological modeling framework at Hunza River Basin of Pakistan Karakoram region

Energy budget‐based distributed modeling of snow and glacier melt runoff is essential in a hydrologic model to accurately describe hydrologic processes in cold regions and high‐altitude catchments. We developed herein an integrated modeling system with an energy budget‐based multilayer scheme for clean glaciers, a single‐layer scheme for debris‐covered glaciers, and multilayer scheme for seasonal snow over glacier, soil, and forest within a distributed biosphere hydrological modeling framework. Model capability is demonstrated for Hunza River Basin (13,733 km 2 ) in the Karakoram region of Pakistan on a 500 m grid for 3 hydrologic years (2002–2004). Discharge simulation results show good agreement with observations (Nash‐Sutcliffe efficiency = 0.93). Flow composition analysis reveals that the runoff regime is strongly controlled by the snow and glacier melt runoff (50% snowmelt and 33% glacier melt). Pixel‐by‐pixel evaluation of the simulated spatial distribution of snow‐covered area against Moderate Resolution Imaging Spectroradiometer‐derived 8 day maximum snow cover extent data indicates that the areal extent of snow cover is reproduced well, with average accuracy 84% and average absolute bias 7%. The 3 year mean value of net mass balance (NMB) was estimated at +0.04 myr −1 . It is interesting that individual glaciers show similar characteristics of NMB over 3 years, suggesting that both topography and glacier hypsometry play key roles in glacier mass balance. This study provides a basis for potential application of such an integrated model to the entire Hindu‐Kush‐Karakoram‐Himalaya region toward simulating snow and glacier hydrologic processes within a water and energy balance‐based, distributed hydrological modeling framework.