Abstract: The topsoil (0-30 cm) water properties of the Sanjiangyuan National Park are an important basis for evaluating regional water conservation and ecological carrying capacity. Results from previous studies are much uncertain due to the lack of field observation data. Based on long-term observations of topsoil water contents in the representative sites across the Qinghai Plateau, combined with the factors such as temperature, precipitation, evapotranspiration, normalized difference vegetation index, elevation, slope, and aspect, the boosted regression trees model was trained to quantify topsoil water storage and water conservation capacity of the Sanjiangyuan National Park. The results showed that the actual topsoil water storage, effective water storage, and water conservation capacity of the Sanjianyuan National Park averaged 75.20±1.98, 50.52±2.53, and 73.79±68.45 mm, respectively. The regional maximum, apparent, and minimum runoff yield averaged 47.75±65.75, -2.78±64.45, and -30.48±65.16 mm, respectively, on the premise of not considering the melting of glaciers and permafrost. The actual topsoil water storage and water conservation in the Sanjianyuan National Park increased from northwest to southeast part. The total stocks of topsoil water storage and water conservation capacity were 30.48×10⁸ and 50.80×10⁸ m³, 79% of which were concentrated in alpine meadows. These findings could provide a data basis for evaluating water resources carrying capacity and functional zoning of the Sanjiangyuan National Park.

Key words: soil water storage, water conservation, runoff yield, boosted regression trees, Sanjiangyuan National Park.