Large-scale coupled hydrologic and hydraulic modelling of the Ob river in Siberia

The Ob river in Western Siberia is one of the largest rivers in the Arctic and has a complex hydrological cycle mainly driven by snow melting in spring and rainfall and evapotranspiration in summer/autumn. The Ob is a source of fresh water for the Arctic Ocean and a change in its regime could affect the ocean thermohaline circulation. Due to the scarcity of in situ measurements in the Arctic and the size of the region, the hydrological modelling of large Arctic rivers is difficult to perform. To model the northern part of the Ob river basin, the land surface scheme ISBA (Interactions between Soil–Biosphere–Atmosphere) has been coupled with the flood inundation model LISFLOOD-FP. Different sensitivity tests on input data and parameters have been performed and the results have been compared with in situ measurements and remotely sensed observations of water level. The best modelling is obtained with a river depth of 10 m and a Manning coefficient of 0.015: correlation and Nash–Sutcliffe coefficients with in situ measurement are equal or even slightly above (depending on the precipitation dataset used) 0.99 and 0.95 respectively. The sensitivity tests show that modelling errors are mainly linked with atmospheric input (snow and rain precipitation), snow cover and drainage parameterization for ISBA and Manning coefficient, river depth and floodplain topography for LISFLOOD-FP.