Simulating cold regions hydrological processes using a modular model in the west of China

Simulating cold regions hydrological processes using a modular model in the west of China

Journal of Hydrology

Summary The Cold Regions Hydrological Model platform (CRHM), a flexible object-oriented modeling system, was devised to simulate cold regions hydrological processes and predict streamflow by its capability to connect cold regions process modules into a purpose-built models. In this study, the cold regions hydrological processes of two basins in western China were evaluated using CRHM: Binggou basin, a high alpine basin where runoff is mainly caused by snowmelt, and Zuomaokong basin, a steppe basin where the runoff is strongly affected by soil freezing/thawing. The flexibility and modular structure of CRHM permitted model structural intercomparison and process falsification within the same model framework to evaluate the importance of snow energy balance, blowing snow and frozen soil infiltration processes to successful modeling in the cold regions of western China. Snow accumulation and ablation processes were evaluated at Binggou basin by testing and comparing similar models that contained different levels of complexity of snow redistribution and ablation modules. The comparison of simulated snow depth with observations during October 30, 2007 to May 6, 2008 shows that the snow accumulation/ablation processes were simulated much better with a physically based snowmelt model, which includes the layered, hourly time step, energy balance snowpack ablation algorithm rather than with a temperature index snowmelt model. Simulated snow sublimation loss could reach up to about 69 cm in the alpine region of Binggou basin, which accounts for 48% of 145.5 cm snowfall, and half of the sublimation loss is attributed to blowing snow, which is about 35 cm. Further comparison of simulated results through falsification of different snow processes reveals that estimating snow sublimation loss is vital for accurate snowmelt calculations in this region. Meanwhile, the model with the energy balance snowmelt and blowing snow components performed well in reproducing the measured streamflow using minimal manual calibration, with R2 (the coefficient of determination for the linear regressions) of 0.83 and NSE values of 0.76. The influence of frozen soil and its thaw on runoff generation was investigated at Zuomaokong basin by comparing streamflow simulated by similar CRHM models with and without infiltration to frozen soil algorithms. The comparison of simulated streamflow with observation shows that the model which included an algorithm describing frozen soil infiltration simulated the main runoff events for the frozen-soil thawing period in spring better than that which used an unfrozen infiltration routine, with R2 (the coefficient of determination for the linear regressions) of 0.87 and NSE values of 0.79. Overall, the test results for the two basins show that cold regions hydrological models using modular modeling structures are sufficiently flexible to take into account the modeling objectives, scale of application, and data constraints and the modular structure can conveniently be varied to compare modeling approaches with different sets of process modules. Therefore, CRHM could successfully simulate cold regions hydrological elements in western China with minimal manual calibration. Given that CRHM and most of its algorithms were developed in western Canada, this is encouraging for predicting hydrology in ungauged cold region basins around the world.