Advancing Understanding of Lake-Watershed Hydrology Through A Fully Coupled Numerical Model

Abstract. Understanding the intricate hydrological interactions between lakes and their surrounding watersheds is pivotal for advancing hydrological research, optimizing water resource management, and informing climate change mitigation strategies. Yet, these complex dynamics are often insufficiently captured in existing hydrological models, such as the bi-direction surface and subsurface flow. To bridge this gap, we introduce a novel lake-watershed coupled model, an enhancement of the Simulator of Hydrological Unstructured Domains (SHUD). This high-resolution, distributed model employs unstructured triangles as its fundamental Hydrological Computing Units (HCUs), offering a physical approach to hydrological modelling. We validated our model using data from Qinghai Lake in China, spanning from 1979 to 2018. Remarkably, the model not only successfully simulated the streamflow of the Buha River, a key river within the Qinghai Lake Basin, achieving a Nash-Sutcliffe efficiency (NSE) of 0.62 and 0.65 for daily and monthly streamflow, respectively, but also accurately reproduced the decrease-increase U-shaped curve of lake level change over the past 40 years, with an NSE of 0.71. Uniquely, our model distinguishes the contributions of various components to the lake's long-term water balance, including river runoff, surface direct runoff, lateral groundwater contribution, direct evaporation, and precipitation. This work underscores the potential of our coupled model as a powerful tool for understanding and predicting hydrological processes in lake basins, thereby contributing to more effective water resource management and climate change mitigation strategies.