Grazing impacts on Mongolian grasslands assessed by an eco-hydrology model

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 m³/year) was the same order of magnitude as mining and urban water uses and that the total water use estimated by this new model was almost similar to that by constant assumption in the previous study. Nevertheless, the model showed that unit water use of sheep has regional variations between 3.11 and 9.80 l/day in each river basin and that the assumption of a constant value as in existing studies does not hold. In addition, the model estimated that goats' water intake was 10% lower than previous assumptions in comparison to other livestock, reflecting an overpopulation of goats over the past 40 years (about tenfold increase) for high demand for cashmere wool and meat products. Furthermore, the simulation clarified heterogeneous distributions of water uses of five types of typical livestock (sheep, horses, cattle, goats, and camels) are indirectly related to the degradation of natural vegetation in grassland. So, the present study uniquely contributes to filling the gap beyond previous studies. The author also detected hot spots of groundwater degradation by human activity including grazing impact in the national scale. These results imply that the excessive use of livestock water intake can lead to groundwater decline, grassland degradation, and ultimately, a reduction in the amount of water available to each livestock head. This methodology is effective to quantify the spatio-temporal variations of livestock water use, to quantify its relation to pasture degradation, and to propose solutions to unsustainable pastoral land use patterns.