Evaluation of spatio-temporal variations in water availability using a process-based eco-hydrology model in arid and semi-arid regions of Mongolia

In Mongolia, overuse and degradation of groundwater is a serious issue, mainly in the urban and economic hub, Ulaanbaatar, and the Southern Gobi mining hub. In order to explicitly quantify spatio-temporal variations in water availability, a process-based eco-hydrology model, NICE (National Integrated Catchment-based Eco-hydrology), was applied to two contrasting river basins: the Tuul River, which is characteristic of northern grassland and steppe, and the Galba River, characteristic of the southern Gobi Desert. The authors built a high-resolution data grid representing water use for livestock, urban populations, and mining in the entire basins by combining a global dataset, statistical data, GIS data, observation data, and field surveys to improve the accuracy of the model results. The model simulated the effects of past climatic change and human-induced disturbances such as urbanization and mining on water resources during 1980–2018 in these two river basins. The model results showed a clear difference in the hydrologic cycle between them, suggesting the impact of urbanization and mining on local-regional eco-hydrological degradation. Although drinking by herders’ livestock had some impact on the hydrologic change, the groundwater level in the Tuul River was shown to have been extremely degraded by water use in Ulaanbaatar over the last few decades whereas that in the Galba River has declined markedly as a result of Oyu Tolgoi mining since 2010. Analysis of the relative contribution of environmental factors also helped us to separate the effects of climatic change and human activities on spatio-temporal change in the groundwater level. These results clarified the large impact of water use due to urbanization and mining on groundwater degradation around the water sources, in addition to climatic change. This methodology is powerful for evaluating spatio-temporal variations of water availability in regions with fewer inventory data on urbanization and mining.