In Mongolia, the traditional pastoral system has changed by the overuse and degradation of water resources. However, there is a research gap between the socio-economic transition and ecosystem degradation on the existing knowledge. In the present study, a process-based eco-hydrology model, National Integrated Catchment-based Eco-hydrology (NICE), was coupled with inverse method (NICE-INVERSE) and applied to the total of 29 river basins in the entire country to quantify the heterogeneous distribution of livestock water use and its relation to pasture degradation there. The result showed that the livestock water use in entire basins (100-120 million m