Application of a Three-Dimensional Coupled Hydrodynamic-Ice Model to Assess Spatiotemporal Variations in Ice Cover and Underlying Mechanisms in Lake Nam Co, Tibetan Plateau, 2007-2017

A three-dimensional lake-ice coupled model is used to investigate the space-time variations of ice and underlying mechanisms in Lake Nam Co (LNC), the third largest lake over Tibetan Plateau (TP), during 2007-2017. The model reasonably reproduces the in situ measured ice thickness and water temperature profile, and satellite retrieved ice coverage and lake surface temperature. Seasonally, the lake ice first forms in the eastern basin during early January, expands from east to west during January and February, covers nearly the entire LNC in March, starts melting from west to east in April, and eventually disappears in May. The eastward drift of thin ice throughout the ice-covered phase and the eastward water heat transport during the ice melting phase are key factors to determine the spatial variation of ice and freeze-thaw processes. A multiple linear regression analysis confirms that the eastward drift of thin ice can be mostly attributed to the prevailing westerly. During 2007-2017, ice volume, duration, ice-on and ice-off dates show significant interannual variations, and they are highly correlated with the surface air temperature (T2m) averaged over January-March, from the preceding December to May, in December and over March-May, respectively, suggesting the "cumulative effects" of T2m. Seasonal and interannual variations of ice drift are attributed to the combined effects of wind and ice volume variations. Sensitivity analysis further points out the important impacts of ice on the lake temperature and circulation structure in winter and spring, hence the necessity of hydrodynamic-ice coupled models in large TP lakes. The space-time variations of ice play fundamental roles in controlling a wide range of physical and biogeochemical processes within lakes, as well as the regional climate, mainly by modulating the lake-air interactions. In this study, we use a three-dimensional lake-ice coupled model to investigate the space-time variations of ice and the underlying mechanisms in Lake Nam Co, the third largest lake over Tibetan Plateau. The numerical model reasonably reproduces the seasonal evolution of ice coverage from satellite remote sensing and ice thickness from in situ observations. Model results reveal that the eastward drift of thin ice throughout the ice-covered phase and eastward water heat transport during the ice melting phase, which are related to the prevailing westerly, are key factors controlling the spatial variation of lake ice. The ice area, volume, duration, ice-on date and ice-off date all show large interannual variability, which can be mostly attributed to the "cumulative effects" of surface air temperature over different preceding months. Analysis of hydrodynamic-ice simulations gains insights on spatiotemporal variations in ice cover and underlying mechanisms in Lake Nam CoEastward drift of thin ice and water heat transport (related to westerly) are main factors determining the spatial variation of lake iceSignificant interannual variations of lake ice volume and phenology are closely related to "cumulative effects" of surface air temperature